Dissertations / Theses on the topic 'Habitat manipulation'

Two widely-recognised hypotheses propose that increases in fish abundance at artificial reefs are caused by: (a) the attraction and redistribution of existing individuals; and/or (b) the addition of new individuals by production. Inadequate experimental designs compromised by a lack of sufficient replication and/or spatial interspersion of reefs with controls have prevented researchers from distinguishing between attraction and production. Infrequent sampling has also led to insufficient temporal coverage of life history-driven variations in fish abundance and biomass at reefs. Detection and resolution of these trends, together with incorporation of fish age/length data, and the use of techniques such as stable isotope analysis to infer trophic link(s) between reef residents and potential sources of epibenthic nutrition at reefs should help demonstrate mechanisms underlying attraction and/or production. Given that fish numbers tend to increase after artificial reef deployments, artificial reefs have been proposed as a means by which fish stocks could be enhanced by providing new habitat in areas where natural habitat vital for feeding, shelter and reproduction have been removed, such as residential canals. The purpose of my study was to investigate whether or not artificial reefs could be used to enhance fish production within residential canals. Five reefs were deployed into Lake Rumrunner on the Gold Coast in southeast Queensland, Australia (28°02’59”S, 153°25’19”E). Reefs were interspersed among five soft sediment (control) sites of similar depth. Fish assemblages at reefs, controls and shoreline jetties were quantitatively sampled using a modified seine pop net. Very few fish were recorded at controls, but fish abundance and biomass increased dramatically at reefs shortly after deployment, stabilising at levels above that of shoreline jetties. Reefs and jetties accommodated different fish assemblages and assemblage structure varied through time. Multivariate analyses indicated that the fish assemblage at jetties within Lake Rumrunner differed from assemblages at jetties in adjacent lakes in terms of biomass composition, accommodating numerous individuals of small-bodied species. The fish assemblage at reefs featured individuals of large-bodied species and occasional, itinerant individuals of species typical of offshore subtidal reefs. Among co-occurring (reef and jetty) fish species, strong differences in the distribution of Monodactylus argenteus (Monodactylidae) between reefs, jetties and controls suggested possible new production driven by reef deployment. Abundance and biomass of M. argenteus was significantly greater at reefs relative to controls (where no fish were caught) and jetties at all times after deployment. Individuals were consistently larger on reefs than on jetties. Analyses of length-frequency distributions through time indicated the size of individuals differed from one sampling time to the next for most sampling times at reefs, possibly representing cohort growth and movement through time...
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment
Science, Environment, Engineering and Technology
Full Text

Trichogramma carverae Oatman and Pinto is mass-released for biological control of the leafroller pest, light brown apple moth, Epiphyas postvittana (Walker) in Australian vineyards. Parasitoid performance can, however, be constrained by a lack of suitable adult food and no information is available on the effect of nectar on the parasitism and longevity of T. carverae. To address this, the effect of alyssum, Lobularia maritima (L.) flowers on E. postvittana parasitism was studied in a vineyard experiment with and without releases of T. carverae. Egg parasitoid activity was assessed with E. postvittana egg 'sentinel cards' and no parasitism was recorded in plots without T. carverae releases. Where T. carverae were released, there was no significant enhancement of parasitism by the presence of L. maritima flowers. Three hypotheses were subsequently tested to account for the lack of an effect: (i) T. carverae does not benefit from L. maritima nectar, (ii) T. carverae was feeding on nectar from other flowering plants (weeds) present in the vineyard, (iii) T. carverae was feeding on sugars from ripe grapes. A growth-cabinet experiment using potted L. maritima plants with and without flowers did not support hypothesis one. No parasitism was recorded after day two for T. carverae caged without flowers whilst parasitism occured until day eight in the presence of flowers. A laboratory experiment with common vineyard weeds (Trifolium repens, Hypochoeris radicata, Echium plantagineum) as well as L. maritima did not support hypothesis one but gave partial support to hypothesis two. Survival of T. carverae was enhanced to a small but statistically significant extent in vials with intact flowers of L. maritima, white clover (T. repens) and catsear (H. radicata) but not in vials with flowering shoots of these species from which flowers and flowering buds had been removed. Paterson's curse (E. plantagineum) flowers had no effect on T. carverae survival. In a laboratory study, punctured grapes significantly enhanced T. carverae survival compared with a treatment without grapes, supporting hypothesis three. Trichogramma carverae performance in the field experiment was probably also constrained by relatively cool and wet weather. Further work on the enhancement of T. carverae efficacy by L. maritima and other carbohydrate sources is warranted. Greenhouse and field experiments were conducted to investigate whether T. carverae benefit from different groundcover plant species. Ten T. carverae adults (<24h after eclosion) were caged with different groundcover species and a control with no plant materials. Epiphyas postvittana egg sentinel cards were used to measure parasitism and longevity was recorded visually. Survival and realised parasitism of T. carverae was significantly higher in L. maritima than in Brassica juncea, Coriandrum sativum, shoots of these species from which flowers had been removed and nil control treatments. A similar experiment with Fagopyrum esculentum (with- and without-flowers) and a control treatment showed that survival was significantly higher in intact F. esculentum than in without-flower and control treatments. There was no significant treatment effect on parasitism in the early stages of that experiment, though parasitism was recorded in the presence of F. esculentum flowers for 12 days, compared with 6 days in other treatments. Higher parasitism was observed in intact Borago officinalis than in the flowerless shoot, water only and no plant material control treatments in a third experiment. There was no significant treatment effect on parasitism. Fitted exponential curves for survival data differed significantly in curvature in the first, second and third experiments but the slope was a non-significant parameter in the second and third experiments. In a second series of laboratory experiments, one male and one female T. carverae were caged with groundcover species to investigate male and female longevity and daily fecundity. Both male and female longevity in F. esculentum and L. maritima treatments were significantly higher than on shoots of these species from which flowers had been removed, and than in the control treatments. Daily fecundity was significantly greater in the intact L. maritima treatment than in all other treatments. Fitted exponential curves for daily fecundity differed significantly in position and slope but not in curvature. There was no significant treatment effect on longevity or parasitism when a male and female were caged with intact B. juncea, B. officinalis or without-flower of these species, nor in the treatment with no plant materials. No parasitism was observed in a survey of naturally occurring egg parasitoids on two sites close to Orange and Canowindra in New South Wales, illustrating the importance of mass releases of T. carverae in biological control of E. postvittana. In an experiment on the Canowindra site, parasitism was significantly higher on day one and day two after T. carverae release when with-flower treatments were compared with without-flower treatments. Parasitism was significantly higher in the F. esculentum treatment than in C. sativum, L. maritima, vegetation without-flowers and control treatments on these dates. On day five, parasitism was higher in C. sativum than in all other treatments. There was no significant increase in parasitism in a second experiment conducted on the Orange site. Coriandrum sativum, F. esculentum and L. maritima appear to be suitable adult food sources for T. carverae and offer some scope for habitat manipulation in vineyards The adults of many parasitoid species require nectar for optimal fitness but very little is known about flower recognition. Flight cage experiments showed that the adults of T. carverae benefited from L. maritima bearing white flowers to a greater extent than was the case for light pink, dark pink or purple flowered cultivars, despite all cultivars producing nectar. Survival and realised parasitism on non-white flowers were no greater than when the parasitoids were caged on L. maritima shoots from which flowers had been removed. The possibility that differences between L. maritima cultivars were due to factors other than flower colour, such as nectar quality, was excluded by dyeing white L. maritima flowers by placing the roots of the plants in 5% food dye (blue or pink) solution. Survival of T. carverae was lower on dyed L. maritima flowers than on undyed white flowers. Mixing the same dyes with honey in a third experiment conducted in the dark showed that the low level of feeding on dyed flowers was unlikely to be the result of olfactory or gustatory cues. Flower colour appears, therefore, to be a critical factor in the choice of plants used to enhance biological control, and is likely to also be a factor in the role parasitoids play in structuring invertebrate communities. Provision of nectar producing plants to increase the effectiveness of biological control is one aspect of habitat manipulation, but care needs to be taken to avoid the use of plant species that may benefit pest species. Greenhouse experiments were conducted to investigate whether the adult E. postvittana and larvae benefit from nectar producing groundcover species. Newly emerged E. postvittana adults were caged with different groundcover species and a honey-based artificial adult diet. The longevity of male and female E. postvittana when caged with shoots of borage (B. officinalis) and buckwheat (F. esculentum) bearing flowers was as long as when fed a honey-based artificial diet. This effect was not evident when caged with shoots of these plants from which flowers had been removed. Longevity was significantly lower than in the artificial diet treatment when caged with coriander (C. sativum) or alyssum (L. maritima) irrespective of whether flowers were present or not. There was no significant treatment effect on the lifetime fecundity of E. postvittana. A second experiment with mustard (B. juncea) (with- and without-flowers), water only and honey-based artificial adult diet showed no significant treatment effects on the longevity of male and female E. postvittana or on the lifetime fecundity of E. postvittana. The anomalous lack of a difference between the water and honey-based diet treatments precludes making conclusions on the value of B. juncea for E. postvittana. Two greenhouse experiments were conducted to evaluate the effects of groundcover species on the larval development of E. postvittana. In the first experiment, larval mortality was significantly higher in C. sativum, and L. maritima than in B. juncea, B. officinalis and white clover (T. repens) a known host of E. postvittana. Coriandrum sativum and L. maritima extended the larval period. In B. juncea and B. officinalis, mortality did not differ from that in T. repens. In F. esculentum, larval mortality was significantly higher than in T. repens. A short larval period was observed on B. juncea, B. officinalis and F. esculentum. Fitted exponential curves for larval mortality differed significantly in curvature between plant treatments. Similarly, successful pupation was significantly lower in C. sativum, F. esculentum and L. maritima than in T. repens. The percentage of successful pupation in B. juncea and B. officinalis did not differ from F. esculentum and T. repens. Fitted exponential curves for pupation differed significantly in curvature. A similar trend was observed in a second experiment with potted plants. The overall results suggest that C. sativum and L. maritima denied benefit to E. postvittana adults and larvae, so could be planted as vineyard groundcover with minimal risk of exacerbating this pest. Overall results suggest that T. carverae require nutrients to reach their full reproductive potential and flowers provide such nutrients. Lobularia maritima and C. sativum may be considered 'selective food plants' for T. carverae whereas F. esculentum appears to be a 'non-selective food plant'; both T. carverae and E. postvittana benefited from it. Fruits such as grapes can be used as food resources in habitat manipulation and this merits further research. This result also suggests that within species flower colour is an important factor for flower selection in habitat manipulation.

Trichogramma carverae Oatman and Pinto is mass-released for biological control of the leafroller pest, light brown apple moth, Epiphyas postvittana (Walker) in Australian vineyards. Parasitoid performance can, however, be constrained by a lack of suitable adult food and no information is available on the effect of nectar on the parasitism and longevity of T. carverae. To address this, the effect of alyssum, Lobularia maritima (L.) flowers on E. postvittana parasitism was studied in a vineyard experiment with and without releases of T. carverae. Egg parasitoid activity was assessed with E. postvittana egg �sentinel cards� and no parasitism was recorded in plots without T. carverae releases. Where T. carverae were released, there was no significant enhancement of parasitism by the presence of L. maritima flowers. Three hypotheses were subsequently tested to account for the lack of an effect: (i) T. carverae does not benefit from L. maritima nectar, (ii) T. carverae was feeding on nectar from other flowering plants (weeds) present in the vineyard, (iii) T. carverae was feeding on sugars from ripe grapes. A growth-cabinet experiment using potted L. maritima plants with and without flowers did not support hypothesis one. No parasitism was recorded after day two for T. carverae caged without flowers whilst parasitism occured until day eight in the presence of flowers. A laboratory experiment with common vineyard weeds (Trifolium repens, Hypochoeris radicata, Echium plantagineum) as well as L. maritima did not support hypothesis one but gave partial support to hypothesis two. Survival of T. carverae was enhanced to a small but statistically significant extent in vials with intact flowers of L. maritima, white clover (T. repens) and catsear (H. radicata) but not in vials with flowering shoots of these species from which flowers and flowering buds had been removed. Paterson�s curse (E. plantagineum) flowers had no effect on T. carverae survival. In a laboratory study, punctured grapes significantly enhanced T. carverae survival compared with a treatment without grapes, supporting hypothesis three. Trichogramma carverae performance in the field experiment was probably also constrained by relatively cool and wet weather. Further work on the enhancement of T. carverae efficacy by L. maritima and other carbohydrate sources is warranted. Greenhouse and field experiments were conducted to investigate whether T. carverae benefit from different groundcover plant species. Ten T. carverae adults (<24h after eclosion) were caged with different groundcover species and a control with no plant materials. Epiphyas postvittana egg sentinel cards were used to measure parasitism and longevity was recorded visually. Survival and realised parasitism of T. carverae was significantly higher in L. maritima than in Brassica juncea, Coriandrum sativum, shoots of these species from which flowers had been removed and nil control treatments. A similar experiment with Fagopyrum esculentum (with- and without-flowers) and a control treatment showed that survival was significantly higher in intact F. esculentum than in without-flower and control treatments. There was no significant treatment effect on parasitism in the early stages of that experiment, though parasitism was recorded in the presence of F. esculentum flowers for 12 days, compared with 6 days in other treatments. Higher parasitism was observed in intact Borago officinalis than in the flowerless shoot, water only and no plant material control treatments in a third experiment. There was no significant treatment effect on parasitism. Fitted exponential curves for survival data differed significantly in curvature in the first, second and third experiments but the slope was a non-significant parameter in the second and third experiments. In a second series of laboratory experiments, one male and one female T. carverae were caged with groundcover species to investigate male and female longevity and daily fecundity. Both male and female longevity in F. esculentum and L. maritima treatments were significantly higher than on shoots of these species from which flowers had been removed, and than in the control treatments. Daily fecundity was significantly greater in the intact L. maritima treatment than in all other treatments. Fitted exponential curves for daily fecundity differed significantly in position and slope but not in curvature. There was no significant treatment effect on longevity or parasitism when a male and female were caged with intact B. juncea, B. officinalis or without-flower of these species, nor in the treatment with no plant materials. No parasitism was observed in a survey of naturally occurring egg parasitoids on two sites close to Orange and Canowindra in New South Wales, illustrating the importance of mass releases of T. carverae in biological control of E. postvittana. In an experiment on the Canowindra site, parasitism was significantly higher on day one and day two after T. carverae release when with-flower treatments were compared with without-flower treatments. Parasitism was significantly higher in the F. esculentum treatment than in C. sativum, L. maritima, vegetation without-flowers and control treatments on these dates. On day five, parasitism was higher in C. sativum than in all other treatments. There was no significant increase in parasitism in a second experiment conducted on the Orange site. Coriandrum sativum, F. esculentum and L. maritima appear to be suitable adult food sources for T. carverae and offer some scope for habitat manipulation in vineyards The adults of many parasitoid species require nectar for optimal fitness but very little is known about flower recognition. Flight cage experiments showed that the adults of T. carverae benefited from L. maritima bearing white flowers to a greater extent than was the case for light pink, dark pink or purple flowered cultivars, despite all cultivars producing nectar. Survival and realised parasitism on non-white flowers were no greater than when the parasitoids were caged on L. maritima shoots from which flowers had been removed. The possibility that differences between L. maritima cultivars were due to factors other than flower colour, such as nectar quality, was excluded by dyeing white L. maritima flowers by placing the roots of the plants in 5% food dye (blue or pink) solution. Survival of T. carverae was lower on dyed L. maritima flowers than on undyed white flowers. Mixing the same dyes with honey in a third experiment conducted in the dark showed that the low level of feeding on dyed flowers was unlikely to be the result of olfactory or gustatory cues. Flower colour appears, therefore, to be a critical factor in the choice of plants used to enhance biological control, and is likely to also be a factor in the role parasitoids play in structuring invertebrate communities. Provision of nectar producing plants to increase the effectiveness of biological control is one aspect of habitat manipulation, but care needs to be taken to avoid the use of plant species that may benefit pest species. Greenhouse experiments were conducted to investigate whether the adult E. postvittana and larvae benefit from nectar producing groundcover species. Newly emerged E. postvittana adults were caged with different groundcover species and a honey-based artificial adult diet. The longevity of male and female E. postvittana when caged with shoots of borage (B. officinalis) and buckwheat (F. esculentum) bearing flowers was as long as when fed a honey-based artificial diet. This effect was not evident when caged with shoots of these plants from which flowers had been removed. Longevity was significantly lower than in the artificial diet treatment when caged with coriander (C. sativum) or alyssum (L. maritima) irrespective of whether flowers were present or not. There was no significant treatment effect on the lifetime fecundity of E. postvittana. A second experiment with mustard (B. juncea) (with- and without-flowers), water only and honey-based artificial adult diet showed no significant treatment effects on the longevity of male and female E. postvittana or on the lifetime fecundity of E. postvittana. The anomalous lack of a difference between the water and honey-based diet treatments precludes making conclusions on the value of B. juncea for E. postvittana. Two greenhouse experiments were conducted to evaluate the effects of groundcover species on the larval development of E. postvittana. In the first experiment, larval mortality was significantly higher in C. sativum, and L. maritima than in B. juncea, B. officinalis and white clover (T. repens) a known host of E. postvittana. Coriandrum sativum and L. maritima extended the larval period. In B. juncea and B. officinalis, mortality did not differ from that in T. repens. In F. esculentum, larval mortality was significantly higher than in T. repens. A short larval period was observed on B. juncea, B. officinalis and F. esculentum. Fitted exponential curves for larval mortality differed significantly in curvature between plant treatments. Similarly, successful pupation was significantly lower in C. sativum, F. esculentum and L. maritima than in T. repens. The percentage of successful pupation in B. juncea and B. officinalis did not differ from F. esculentum and T. repens. Fitted exponential curves for pupation differed significantly in curvature. A similar trend was observed in a second experiment with potted plants. The overall results suggest that C. sativum and L. maritima denied benefit to E. postvittana adults and larvae, so could be planted as vineyard groundcover with minimal risk of exacerbating this pest. Overall results suggest that T. carverae require nutrients to reach their full reproductive potential and flowers provide such nutrients. Lobularia maritima and C. sativum may be considered �selective food plants� for T. carverae whereas F. esculentum appears to be a �non-selective food plant�; both T. carverae and E. postvittana benefited from it. Fruits such as grapes can be used as food resources in habitat manipulation and this merits further research. This result also suggests that within species flower colour is an important factor for flower selection in habitat manipulation.

Paropsis atomaria Olivier (Coleoptera: Chrysomelidae: Paropsini), is a major pest of commercially grown eucalypts in South-East Queensland. Current management of paropsine beetles involves regular inspection and the application of chemical sprays if defoliation is severe. However, non-chemical control of plantation pests is highly desirable given the requirement to certify forest practices for sustainability, and community concerns over the use of pesticides. One way of reducing pesticide use is through conservation biological control, which requires detailed knowledge of the life history of the pest and its natural enemies. This thesis documents aspects of P. atomaria phenology, including life tables, sex ratios and damage estimates; identifies the predators, parasites, and egg and larval parasitoids of P. atomaria; and examines the ecology of the most promising natural enemy, Neopolycystus Girault sp. (Hymenoptera: Pteromalidae) in South-East Queensland. P. atomaria adults are active from September until April and can complete up to four generations in a season. Field mortality between egg and fourth instar larvae is approximately 94%. A large proportion of this mortality can be attributed to natural enemies. The most abundant predators in eucalypt plantations were spiders, comprising 88% of all predators encountered. Egg parasitoids exerted the greatest influence on P. atomaria populations, emerging from around 50% of all egg batches, and were responsible for mortality of almost one third of all eggs in the field. Only about one percent of larvae were parasitised in the field, in contrast to paropsine pests in temperate Australia, where egg parasitism rates are low and larval parasitism rates high. Neopolycystus sp. was the only primary parasitoid reared from P. atomaria eggs, along with three hyperparasitoid species; Baeoanusia albifunicle Girault (Encyrtidae), Neblatticida sp. (Encyrtidae) and Aphaneromella sp. (Platygasteridae). This is the first record of B. albifunicle hyperparasitising Neopolycystus spp. B. albifunicle emerged from one-third of all parasitised egg batches and could pose a potential problem to the efficacy of Neopolycystus sp. as a biological control agent. However, within egg batches, hyperparasitoids rarely killed all Neopolycystus sp. with only 9% of hyperparasitised egg batches failing to produce any primary parasitoids. Total field mortality of P. atomaria through direct and indirect effects of parasitism by Neopolycystus sp. was 28%. The proportion of egg batches parasitised increased with exposure time in the field, but within-batch parasitism rate did not. In general, there was no significant correlation between parasitism rates and distance from landscape features (viz. water sources and native forest).

Paropsis atomaria Olivier (Coleoptera: Chrysomelidae: Paropsini), is a major pest of commercially grown eucalypts in South-East Queensland. Current management of paropsine beetles involves regular inspection and the application of chemical sprays if defoliation is severe. However, non-chemical control of plantation pests is highly desirable given the requirement to certify forest practices for sustainability, and community concerns over the use of pesticides. One way of reducing pesticide use is through conservation biological control, which requires detailed knowledge of the life history of the pest and its natural enemies. This thesis documents aspects of P. atomaria phenology, including life tables, sex ratios and damage estimates; identifies the predators, parasites, and egg and larval parasitoids of P. atomaria; and examines the ecology of the most promising natural enemy, Neopolycystus Girault sp. (Hymenoptera: Pteromalidae) in South-East Queensland. P. atomaria adults are active from September until April and can complete up to four generations in a season. Field mortality between egg and fourth instar larvae is approximately 94%. A large proportion of this mortality can be attributed to natural enemies. The most abundant predators in eucalypt plantations were spiders, comprising 88% of all predators encountered. Egg parasitoids exerted the greatest influence on P. atomaria populations, emerging from around 50% of all egg batches, and were responsible for mortality of almost one third of all eggs in the field. Only about one percent of larvae were parasitised in the field, in contrast to paropsine pests in temperate Australia, where egg parasitism rates are low and larval parasitism rates high. Neopolycystus sp. was the only primary parasitoid reared from P. atomaria eggs, along with three hyperparasitoid species; Baeoanusia albifunicle Girault (Encyrtidae), Neblatticida sp. (Encyrtidae) and Aphaneromella sp. (Platygasteridae). This is the first record of B. albifunicle hyperparasitising Neopolycystus spp. B. albifunicle emerged from one-third of all parasitised egg batches and could pose a potential problem to the efficacy of Neopolycystus sp. as a biological control agent. However, within egg batches, hyperparasitoids rarely killed all Neopolycystus sp. with only 9% of hyperparasitised egg batches failing to produce any primary parasitoids. Total field mortality of P. atomaria through direct and indirect effects of parasitism by Neopolycystus sp. was 28%. The proportion of egg batches parasitised increased with exposure time in the field, but within-batch parasitism rate did not. In general, there was no significant correlation between parasitism rates and distance from landscape features (viz. water sources and native forest).

My research provided new information concerning the management, ecology, and conservation of greater sage-grouse (Centrocercus urophasianus). I report the results of an experiment using strategic intensive sheep grazing to enhance the quality of greater sage-grouse brood-rearing habitat. Although forb cover, an important component of brood-rearing habitat, responded positively to the grazing treatment, the response of other habitat variables was suppressed because the plots were not protected from domestic and wild herbivores during the years following the treatments. Measurements taken in grazing exclosures confirmed that herbivory by both large and small animals had significant impacts on vegetation. However, despite the suppressed habitat response, sage-grouse preferred the treated plots over the controls. In another chapter, I modeled survival rates of sage-grouse chicks to 42-days of age. Average chick survival across my study was high (39%). Survival varied across years and was affected by demographic, behavioral, and habitat factors. The top habitat model indicated that chick survival was positively related to grass cover and was higher in areas dominated by black sagebrush (Artemisia nova) than in big sagebrush (A. tridentata). The top model with demographic/behavioral factors indicated that survival was affected by interactions between hen age and brood mixing as well as between hatch date and brood mixing. In my last chapter I report on a survey of Utah sage-grouse hunter motivations and satisfaction. In 2008 and 2009 I surveyed over 600 sage-grouse hunters in Utah to determine why they chose to apply for sage-grouse hunting permits and what factors contributed to a satisfactory hunting experience. Originally, I had hypothesized that the impending Endangered Species Act listing petition for greater sage-grouse motivated hunters to pursue the species before they lost the opportunity. This hypothesis was not supported by the data. The majority of hunters indicated that they chose to hunt sage-grouse because it was a tradition or because it provided an opportunity to spend time outdoors with family. Additionally, Utah sage-grouse hunter satisfaction was influenced by whether or not the hunter was successful in harvesting at least one bird.

Le specie aliene invasive sono specie animali o vegetali che molto spesso vengono introdotte involontariamente in ecosistemi non autoctoni, con impatto negativo per l'ambiente e le attività umane. La Drosophila suzukii Matsumura (Diptera: Drosophilidae), nota anche come Spotted Wing Drosophila, è una specie aliena invasiva originaria dell'Asia orientale, che si è ampiamente diffusa nelle Americhe e in Europa, dove è divenuta un grave parassita delle colture frutticole, causando notevoli perdite economiche. In Trentino la prima segnalazione di questo insetto su ospiti coltivati è avvenuta nel 2009. La sua rapida diffusione in tutto il mondo è attribuita a delle caratteristiche peculiari di D. suzukii, come l'ovopositore seghettato che gli consente di deporre le uova in frutti sani in maturazione, l’ampia gamma di piante ospiti, l’elevata fecondità e la tolleranza nei confronti di un ampio spettro di condizioni climatiche, fattori che ne ha aumentano significativamente l'invasività. Gli attuali approcci per il controllo di D. suzukii si basano principalmente su strategie di gestione integrata dei parassiti, tra cui il controllo chimico, le reti anti-insetto, la cattura massale e pratiche culturali, come la potatura delle chiome, l'irrigazione a goccia e il sollecito allontanamento della frutta infestata dai campi nel corso della raccolta. Analogamente ad altri parassiti invasivi, D. suzukii non viene efficacemente controllata da parte dei nemici naturali nelle aree invase, consentendogli di riprodursi rapidamente e diffondersi illimitatamente, aumentando la pressione dei parassiti sulle coltivazioni. Il controllo biologico inondativo e quello classico, sono in corso di valutazione e potrebbero diventare dei promettenti candidati per limitare i focolai stagionali di D. suzukii e i relativi danni alle colture. Tuttavia, nonostante i notevoli passi in avanti sulle conoscenze della biologia e l'ecologia di D. suzukii, questo insetto rappresenta ancora una seria minaccia per le colture e vi è la necessità di ulteriori studi al fine di aggiornare gli strumenti di gestione a disposizione per far fronte a questo importante parassita delle colture. Nel corso dei monitoraggi faunistici in provincia di Trento, abbiamo riscontrato e segnalato per la prima volta in Europa la presenza del parassitoide larvale asiatico Leptopilina japonica Novkovic & Kimura (Hymenoptera: Figitidae), uno dei più efficaci nemici naturali di D. suzukii nell’areale nativo. L’esteso monitoraggio in campo successivo al primo ritrovamento ha permesso di stabilire l'elevata capacità di questo parassitoide di parassitare il suo ospite su un ampio spettro di specie vegetali, appartenenti a diverse famiglie tassonomiche come Moraceae, Rosaceae, Glossulariaceae, Rhamnaceae, Cornaceae, Ericaceae, Phytolaccaceae, Dioscoreaceae, Adoxaceae e Solanaceae. Questi risultati offrono nuove prospettive per il controllo biologico di D. suzukii nelle aree di recente introduzione, anche per quanto concerne i futuri programmi di controllo biologico classico con Ganaspis brasiliensis Ihering (Hymenoptera: Figitidae). Il controllo biologico per mezzo di parassitoidi o predatori può essere facilmente integrato con la tecnica dell'insetto sterile (SIT), potenziando il controllo sulle popolazioni di parassiti. Tuttavia, il successo della SIT è in gran parte influenzato dal sistema riproduttivo del parassita bersaglio, per cui l’approfondimento dei tratti riproduttivi è un prerequisito fondamentale per verificare l’effettiva applicabilità di questa tecnica di controllo. L'analisi della paternità mediante la genotipizzazione di loci microsatellite della progenie di femmine catturate in natura, ha rilevato elevati livelli di paternità multipla nelle covate genotipizzate, stabilendo il comportamento poliandro di D. suzukii, sebbene non sia stata rilevata alcuna distorsione della paternità nell'allocazione dello sperma, ovvero in termini di maschio prevalenza. Oltre al controllo biologico e alla SIT, le strategie basate sulla manipolazione dell'habitat potrebbero utilmente integrare le comuni pratiche culturali messe in atto dagli agricoltori per il controllo di D. suzukii. Le nostre prove in campo hanno dimostrato che la consociazione con Mentha x piperita (Menta piperita, Lamiaceae) Origanum vulgare L. (Origano, Lamiaceae), Thymus vulgaris L. (Timo, Lamiaceae) o Ocimum gratissimum L. (Basilico africano, Lamiaceae), non risulta avere un impatto positivo nel limitare i danni causati da D. suzukii su colture di mirtillo, mentre la realizzazione di una bordura di Prunus padus (ciliegio europeo, Rosacee) si è dimostrata in grado di ridurre l'infestazione su di una coltura di lampone, agendo come pianta trappola. Inoltre, il controllo biologico conservativo mediante la tecnica dell’augmentorium può offrire un’ulteriore integrazione agli strumenti di controllo. Abbiamo infatti potuto osservare come il nostro prototipo si è dimostrato adatto per una sua applicazione su D. suzukii e sui relativi parassitoidi indigeni, favorendo la sanificazione delle colture dai frutti infestati e sostenendo i più comuni parassitoidi pupali. Con questa ricerca abbiamo inteso verificare l’efficacia di nuovi strumenti di controllo di D. suzukii, quali il controllo biologico, sia conservativo che classico, la SIT e la manipolazione dell'habitat, la cui opportuna integrazione offrirebbe la possibilità di implementare un approccio agroecologico di gestione di questo parassita invasivo.
Invasive alien species are animal or plant species that are very often unintentionally introduced into non-native ecosystems, with negative impact for the environment and human activities. Drosophila suzukii Matsumura (Diptera: Drosophilidae), also known as Spotted Wing Drosophila, is an invasive alien species native to East Asia, which has widely established in Americas and Europe, where it has become a serious pest of fruit crops, causing considerable economic losses. In Trentino Province the first oviposition on crop hosts was reported in 2009. The rapid worldwide spread is attributed to peculiar features of D. suzukii, such as the serrated ovipositor that allows it to oviposit into healthy ripening fruits, broad host plants range, high fecundity potential and tolerance of wide climatic conditions. Current approaches for controlling D. suzukii rely primarily on integrated pest management strategies, including chemical control, insect-proof netting, mass trapping and cultural practices, such as canopy pruning, drip irrigation, and field sanitation. Similarly to other invasive pest, D. suzukii lacks of an effective suppression by natural enemies in the recently invaded areas, enabling it to reproduce quickly and spread unlimitedly, increasing pest pressure on cropping systems. Augmentative and classical biological control are still under investigation as promising candidates for limiting D. suzukii seasonal outbreaks and related damage on crops. However, despite the remarkable steps forward in the knowledge on biology and ecology of D. suzukii, it is still a serious threat to crops and further investigations are urgently required in order to update the availability of management tools to cope with this crop pest. During our faunistic surveys in Trentino province, we found and reported for the first time in Europe, the presence of the Asian larval parasitoid Leptopilina japonica Novkovic & Kimura (Hymenoptera: Figitidae), one of the most effective natural enemies of D. suzukii in the native range. The following extensive field monitoring based on fruit sampling revealed the high capacity of this parasitoid to parasitize its host on a complex of several plant species, belonging to Moraceae, Rosaceae, Glossulariaceae, Rhamnaceae, Cornaceae, Ericaceae, Phytolaccaceae, Dioscoreaceae, Adoxaceae and Solanaceae. These findings offer new perspective for biological control of D. suzukii in the introduced areas, also in relation to the classical biological control programmes with Ganaspis brasiliensis Ihering (Hymenoptera: Figitidae). Biological control by means of parasitoids or predators can be easily integrated with sterile insect technique (SIT), synergizing the control effects on pest population. Nevertheless, the success of SIT is largely influences by mating system of target pest, thus deepen reproductive traits is a fundamental step forward. Paternity analysis by means of microsatellite loci genotyping of the progeny of wild-caught females, detected high levels of multiple paternity in genotyped broods, stating the polyandrous behaviour of D. suzukii, but no found evidence of a strong paternity skew in sperm allocation, in terms of prevailing male. Beyond biological control and SIT, habitat manipulation strategies may further help local farmers to deal with D. suzukii in addition to common applied cultural practices. Our field trials have shown that intercropping with Mentha x piperita (Peppermint, Lamiaceae) Origanum vulgare L. (Oregano, Lamiaceae), Thymus vulgaris L. (Thyme, Lamiaceae), or Ocimum gratissimum L. (African basil, Lamiaceae), has no effect in limiting the damage of D. suzukii on blueberries, whilst hedges of Prunus padus (European bird cherry, Rosaceae) was able to reduce the infestation on raspberry, having a potential role as dead-end trap plant for crop protection against D. suzukii. Furthermore, conservative biological control by means of the augmentorium technique may be further explored, as we observed that our prototype has shown to be well adapted to D. suzukii and its indigenous parasitoids, favouring crop sanitation from infested fruits and sustaining the most common Drosophila pupal parasitoids. This research aims to give new insights for a more sustainable management of D. suzukii, offering new solutions that, by combining biological control, both conservative and classical, SIT and habitat manipulation, may move towards an agroecological approach for controlling this invasive pest.

The Utah prairie dog (Cynomys parvidens) was listed by the U.S. Fish and Wildlife Service as an endangered species in 1973 because of range-wide population declines. The species was reclassified as threatened in 1984 because of population increases on private lands. Habitat fragmentation coupled with a lack of suitable habitat has impeded species recovery. Desired species habitat conditions include 0-8% shrub cover, 12-40% cool-season grass cover, and 1-10% perennial forb cover. Cool-season grasses are critical for Utah prairie dogs because of high spring energy requirements. Past research suggested that reducing shrub cover may increase cover of desired grasses and forbs. From 2008-2010, I evaluated the effects of high intensity fall sheep grazing and low application of herbicide (tebuthiuron) as tools to reduce shrub cover and enhance grass and forb cover on the Awapa Plateau Utah prairie dog recovery area in south-central Utah. I placed 1700 ewes in 4 ha stratified and randomly selected plots until >70% vegetation utilization was achieved. Five additional randomly-selected plots were treated with tebuthiuron at a rate of ~1.68 kg/ha. Percent cover of grass, forbs, and shrubs was recorded on treatments and paired control plots in June 2009 and 2010 to determine treatment vegetation responses. I also affixed 22 juvenile Utah prairie dogs with radio transmitters to determine if over-winter survival differed relative to treatment. Live shrub cover was lower on grazed plots in year 1 (P<0.001) and in year 2 (P=0.015). Dead shrub cover in grazed plots was higher in year 1 (P<0.001). Grazed plots exhibited increased forb cover from year 1 (P=0.104) to year 2 (P=0.008). Live shrub cover was lower in herbicide plots in year 2 (P=0.002). Dead shrub cover in herbicide plots was higher in year 2 (P=0.006). Tebuthiuron and grazed plots exhibited a reduction in shrub height (P=0.010, P=0.026, respectively). Tebuthiron plots exhibited less grass cover (P=0.034). Intensive sheep grazing and a low application of tebuthiuron reduced both shrub cover and vertical structure, but failed to increase the percent of grass cover when compared to the control plots. All plots exhibited reduced grass cover in 2010 in response to below normal precipitation. However, percent grass cover was higher on the grazed plots. It is possible that low inherent site productivity in combination with below normal average precipitation compromised treatment effects. Because of radio transmitter failure, I was not able to obtain survival data after hibernation. Prairie dog counts and weights did not differ by treatment type. If climate change reduces overall precipitation on the Awapa Plateau, recovery of the Utah prairie dog on this site will be problematic.

Declining greater sage-grouse populations (Centrocercus urophasianus; hereafter sage-grouse) have led to increased concern regarding the long-term stability of the species. Previous research has identified factors contributing to the observed population declines. Habitat degradation and loss have been implicated as major factors in population declines. Although much is known about sage-grouse biology, more information is needed about population responses to specific management actions. This research was conducted to document sage-grouse responses to site-specific management actions. Additionally, I evaluated sage-grouse temporal and seasonal habitat-use and the comparability of techniques used by range and wildlife managers to measure vegetation responses of habitat management. Specifically, I evaluated 1) whether chemical analysis (gas chromatography) of sage-grouse fecal pellets could identify sagebrush species in sage-grouse winter diets, 2) the comparability of the line-point intercept and Daubenmire canopy cover methods for estimating canopy cover, 3) the response of sage-grouse broods to prescribed burns in a high elevation sagebrush community in northeastern Utah, and 4) the vegetation and insect characteristics of sites used by sage-grouse broods during a 24-hour period. I was able to determine wintering sage-grouse diets using gas chromatography by analyzing fecal pellets. This research also confirmed that black sagebrush (Artemisia nova) was an important component of sage-grouse winter diets in western Box Elder County and Parker Mountain populations. The line-point intercept and Daubenmire methods for estimating canopy cover are not comparable. Sage-grouse broods selected small (~ 25 ha) patchy prescribed burns in high elevation mountain big sagebrush (A. tridentata vaseyana) communities in northeastern Utah. Sage-grouse brood-site use in northwestern Utah did not differ during the diurnal hours, but nocturnal roost sites were characterized by shorter statured shrubs and more bare ground when compared to midday sites.

The greater sage-grouse (Centrocercus urophasianus; sage-grouse) has been a species of conservation concern since the early 20th century due to range-wide population declines. To contribute to knowledge of the ecology of sage-grouse populations that inhabit the Box Elder Sage Grouse Management Area (SGMA) in northwestern Utah and quantify their responses to landscape scale habitat manipulations, I monitored vital rates and habitat selection of 45 female sage-grouse from 2014 to 2015. Using telemetry locations of female sage-grouse with known nest and brood fates, I created Generalized Linear Mixed Models to estimate the influence of proximity to pinyon (Pinus spp.) and juniper (Juniperus spp.; conifer) encroachment, and removal projects may have on sagegrouse reproductive fitness in the Box Elder SGMA. The best fit model suggested that for every 1 km a nest was located away from a conifer removal area, probability of nest success was reduced by 9.1% (β = -0.096, P < 0.05). Similarly, for every 1 unit increase in the log-odds of selection for distance to treatment, probability of brood success declined by 52.6% (P = 0.09). The probability of brood success declined by 77.2% (P < 0.05) as selection for conifer canopy cover increased. To evaluate sage-grouse habitat use, I used fecal pellet surveys to estimate relative pellet density in conifer encroachment, removal, and undisturbed sagebrush areas. Sage-grouse pellet densities were estimated at 4.6 pellets/ha (95% CI = 1.2, 10.9), 8.6 pellets/ha (95% CI = 3.8, 15.2), and 50.6 pellets/ha (95% CI = 36.8, 69.6), in conifer encroachment, removal, and undisturbed sagebrush areas respectively. Density estimates did not statistically differ between conifer encroachment and removal areas. To determine if vegetation micro-site characteristics at sage-grouse use sites influenced nest or brood fate, I recorded standard vegetation measurements for all radio-marked sage-grouse nests and a stratified random sample of brood-use sites from 2014- 2015 and compared them to random sites. Micro-site vegetation characteristics measured did not differ for successful and unsuccessful nests. Many characteristics differed between micro-sites used by successful broods and those used by unsuccessful broods. Sites used by successful broods also differed from random sites.

Experiments were conducted to assess whether a concept termed 'attract and reward' (A&R) could enhance conservation biological control (CBC). In A&R, a synthetically-produced herbivore induced plant volatile (HIPV) ('attract') is combined with a floral resource ('reward'). It is anticipated that the two will work synergistically attracting natural enemies into the crop ('attract') and maintaining them within the crop ('reward'). The study system consists of brassica, the most commonly occurring brassica herbivores, their natural enemies and higher order natural enemies. The HIPV deployed is methyl salicylate (MeSA) and the floral resource is buckwheat Fagopyrum esculentum. The aim of the first two field experiments, in 2007 and 2008, was to evaluate the effects of MeSA and MeSA combined with buckwheat (A&R) on the abundance of arthropods from three trophic levels. In 2007, a field experiment was conducted using MeSA alone. The mean abundance of the leafmining fly Scaptomyza flava (trophic level 2), the diamondback moth (trophic level 2)(DBM) parasitoid Diadegma semiclausum (trophic level 2) and the hoverfly Melangyna novaezealandiae (trophic level 3) was increased in MeSA-treatments by up to 300% and for the brown lacewing parasitoid Anacharis zealandica a maximum mean increase of 600% was recorded. Significantly more females of the D. semiclausum and M. novaezealandiae were attracted to MeSA than males. When A&R was deployed in 2008, were arthropods from the third and fourth trophic levels affected. For none of the species was there a synergistic effect between 'attract' and 'reward' on their abundance. The brown lacewing Micromus tasmaniae (trophic level 3), two parasitoids of DBM and one of cabbage white butterfly Pieris rapae (trophic level 2) increased significantly in treatments with buckwheat. The hoverfly Melanostoma fasciatum (trophic level 3) was significantly more abundant in treatments with MeSA, but significantly less abundant in treatments with buckwheat. The effect of MeSA on the fourth trophic level parasitoid Anacharis zealandica (trophic level 4) was inconsistent between years. Here it significantly decreased its abundance, while treatments with buckwheat increased it. Significantly fewer male than female D. semiclausum were attracted to MeSA only treatments. These experiments show that MeSA and buckwheat can have unwanted effects on arthropod abundance which may disrupt CBC. To assess the effect of A&R on CBC a further field experiment evaluating herbivore densities, predation, parasitism and hyper-parasitism rates was conducted. The only effect was significantly higher aphid parasitism in treatments with MeSA. Based on the results from the field experiments it remained unclear whether it was MeSA or a blend of volatiles produced by MeSA-induced host plants that were attractive to the arthropods. An olfactory experiment was conducted to evaluate if the aphid parasitoid Aphidius colemani can be attracted to two different concentrations of MeSA diluted in Synertrol oil. Significantly more parasitoids were attracted to 2.0% MeSA than to air while the parasitoid did not respond to the 0.5% concentration. These results indicate that A&R has potential as a CBC technique, as long as any unwanted side effects can be managed. Although there were no synergistic effects between 'attract' and 'reward' on the abundance of individual natural enemies, combining MeSA and buckwheat could still be beneficial because the two techniques increase the abundance of different natural enemies.

In this study, buckwheat (Fagopyrum esculentum Moench) and alyssum (Lobularia maritima (L.)) flowers were used to examine the effect of floral resources on the efficacy of the leafroller parasitoid Dolichogenidea tasmanica (Cameron) in vineyards. This was done by assessing the influence of these flowers on parasitoid abundance and parasitism rate, and by investigating the consequences of this for leafroller abundance. In laboratory experiments, alyssum flowers were used to investigate the effect of floral food on the longevity, fecundity and sex ratio of D. tasmanica. Dolichogenidea tasmanica comprised more than 95 % of parasitoids reared from field collected leafrollers in this study. The abundance of D. tasmanica during the 1999-2000 growing season was very low compared with previous studies, possibly due to the very low abundance of its leafroller hosts during the experiment. The number of males of this species on yellow sticky traps was increased (although not significantly) when buckwheat flowers were planted in a Marlborough vineyard; however, the number of female D. tasmanica on traps was no greater with flowers than without. The abundance of another leafroller parasitoid, Glyptapanteles demeter (Wilkinson)(Hymenoptera: Braconidae), on traps was also not significantly affected by the presence of buckwheat flowers, although females of this species were caught in greater numbers in the control than in buckwheat plots. Naturally-occurring leafrollers were collected from three vineyard sites in Marlborough, and one in Canterbury during the 2000-2001 season to assess the effect of buckwheat and alyssum flowers on parasitism rate. Parasitism rate more than doubled in the presence of buckwheat at one of the Marlborough vineyards, but alyssum had no effect on parasitism rate in Canterbury. A leafroller release/recover method, used when naturally-occurring leafrollers were too scarce to collect, was unable to detect any effect of buckwheat or alyssum on parasitism rate. Mean parasitism rates of approximately 20 % were common in Marlborough, although rates ranged from 0 % to 45 % across the three vineyard sites in that region. In Canterbury in April, mean parasitism rates were approximately 40 % (Chapter 4). Rates were higher on upper canopy leaves (40-60 %) compared with lower canopy leaves and bunches (0-25 %). Leafroller abundance was apparently not affected by the presence of buckwheat in Marlborough, or alyssum in Canterbury. Buckwheat did, however, significantly reduce the amount of leafroller evidence (webbed leafroller feeding sites on leaves or in bunches) in Marlborough, suggesting that the presence of these flowers may reduce leafroller populations. Leafrollers infested less than 0.1 % of Cabernet Sauvignon leaves throughout the 1999-2000 growing season, but increased in abundance in bunches to infest a maximum of 0.5 % of bunches in late March in Marlborough. In Pinot Noir vines in the 2000-2001 season, leafroller abundance was also low, although sampling was not conducted late in the season when abundance reaches a peak. In Riesling vines in Canterbury, between 1.5 % and 2.5 % of bunches were infested with leafrollers in April. In the laboratory, alyssum flowers significantly increased the longevity and lifetime fecundity of D. tasmanica compared with a no-flower treatment. However, daily fecundity was not increased by the availability of food, suggesting that the greater lifetime fecundity was related to increases in longevity. Parasitoids were also able to obtain nutrients from whitefly honeydew, which resulted in similar longevity and daily fecundity to those when alyssum flowers were present. The availability of food had a significant effect on the offspring sex ratio of D. tasmanica. Parasitoids reared from naturally-occurring leafrollers produced an equal sex ratio, assumed to be the evolutionarily stable strategy (ESS) for this species. In the laboratory, this ESS was observed only when parasitoids had access to alyssum flowers. Without food, or with honeydew only, sex ratios were strongly male-biased. In the field, floral resources affected the sex ratio of D. tasmanica only when this species was reared from leafrollers released and recovered in Marlborough. In that experiment, buckwheat shifted the sex ratio in favour of female production from the equal sex ratio found in control plots. No firm explanations can be given to account for these results, due to a lack of research in this area. Possible mechanisms for the changes in sex ratio with flowers are discussed. This study demonstrated that flowers are an important source of nutrients for D. tasmanica, influencing the longevity, fecundity and offspring sex ratio of this species. However, only some of the field experiments were able to show any positive effect of the provision of floral resources on parasitoid abundance or parasitism rate. More information is needed on the role these parasitoids, and other natural enemies, play in regulating leafroller populations in New Zealand vineyards, and on how they use floral resources in the field, before recommendations can be made regarding the adoption of this technology by growers.

This dissertation was submitted to the Faculty of Science, University of the Witwatersrand, in fulfillment of the requirements for the degree of Master of Science
Dung beetle feeding is still not a widely understood behaviour. Feeding on the waste of other animals creates a challenge of acquiring the necessary nutrients for growth, development and for survival. Because of their soft mouthparts, it has always been thought that adult dung beetles cannot chew the hard parts of dung but only select smaller particles to feed on. Dung beetle larvae on the other hand can chew harder components, but where they get the nutrients required for development has not yet been discovered. The aim of this study was to discover which dung particles adult dung beetles select when feeding, and when creating a nest for their offspring, and also how much they can alter the dung nutrient content in the process. Foregut and hindgut contents were dissected out of the dung beetle Scarabaeus goryi, and their contents compared with untreated dung from the cow and the excreta of adult beetles. Brood balls and maternal gifts of Euoniticellus intermedius were also dissected. Nitrogen and carbon content, the carbon to nitrogen ratio, and results of the carbon and nitrogen stable isotopes were compared between all samples. When feeding dung beetles selected particles which were bigger than 800 μm in diameter and had three times more nitrogen than raw dung, and used particles over 2000 μm in size in the maternal gift packed for their offspring. Nitrogen content in the selected dung was increased from 1.40 % to 5.14% by adult dung beetle feeding and up to 2.62% in dung selected for the larvae to feed on. The carbon to nitrogen ratio also decreased when feeding adults and in the brood balls made for the larvae to feed on. Both carbon and nitrogen were absorbed from ingested dung during digestion. The heavier nitrogen isotope was selected for when feeding. The heavier nitrogen isotopes and the lighter carbon isotope were selected for during absorption. Dung beetles increase the nitrogen content of the dung on which they feed by careful selection of particles of a certain size and nitrogen content, which is probably the limiting nutrient when feeding and nesting. The increase in the nitrogen content is not only from the change in particle size but also in selection of particles with higher nitrogen content.
MT2018

Research Doctorate - Doctor of Philosophy (PhD)
This thesis investigated the potential of water salinity to limit the pathogenicity of Bd (the amphibian chytrid fungus) in a created habitat mosaic. Results demonstrate that determining the outcomes of varying aquatic habitat treatments in a constructed, constrained system is a complex problem, with many interactions. Nevertheless, there was no evidence that any of the habitat components (treatments) incorporated into the experimental design negatively impacted the fitness, or reduced the survival of the model amphibian species, Litoria aurea. The results of this thesis in fact suggest that the most appropriate strategy for optimising the probability of persistence of L. aurea in a landscape in which they have been shown to persist, is to offer a landscape mosaic of waterbodies of varying hydroperiod and salinity. Such a mosaic offers choice for optimal breeding and dispersal throughout the seasonal climatic cycle, while exposing individuals, even intermittently, to elevated salinities that may confer survival across the whole habitat. Taken together, these environmental variables in a complex mosaic may tip the balance of population dynamics from decline and extinction towards persistence. The implications of this approach extend beyond L. aurea to the management of other amphibian species that persist with Bd in complex environments.