Presence Of Tadpoles Research Articles

Invasion of a non‐native anuran likely disrupts pond ecosystems

Abstract Freshwater ecosystems worldwide are under increasing pressure from multiple threats, including invasive species and climate change, with ponds being particularly vulnerable because of their shallow depth and dynamic hydrology. Australian brown tree frogs Litoria ewingii, introduced to New Zealand in 1875, have spread across both main islands, breeding in a large range of shallow fishless ponds. Since native frogs do not produce aquatic tadpoles, any tadpole influence will be novel, so these ecosystems may be especially vulnerable to such influences. To determine the functional role of L. ewingii tadpoles and to uncover potential effects on pond community structure and function, we conducted two 3‐week‐long mesocosm experiments. The first crossed tadpole presence with predatory invertebrate presence. Mesocosms containing tadpoles had a lower biomass of periphyton and macrophytes, and lower abundance of two families of small‐sized invertebrates (Culicidae and Chironomidae) compared to mesocosms without tadpoles, possibly as a consequence of grazing, predation or reduced dipteran oviposition. However, predatory invertebrates did not affect tadpoles except at their smallest stage, so L. ewingii probably are not subject to strong top‐down control by invertebrates in fishless ponds. We evaluated the effects of tadpole density on ecosystem processes in the second experiment where half the mesocosms also were shaded to simulate permanent pond hydrological status; shading stabilised the temperature fluctuations typical of temporary ponds. In shaded mesocosms tadpole density did not change phytoplankton, whereas in unshaded mesocosms, phytoplankton biomass increased with tadpole density, possibly because tadpole excretion enhanced algal growth in high light conditions. Higher densities of tadpoles also decreased dissolved oxygen concentration regardless of shading during the day—potentially an indirect effect of grazing on macrophytes and periphyton reducing photosynthesis. Overall, these non‐native tadpoles are likely to be having large influences on ecosystem processes such as nutrient cycling in small ponds, especially when at high densities. In light of these potential effects on pond ecosystems, and the generalist traits of these frogs which could see them spread to even remote alpine ponds, control measures to prevent further range expansion should be considered in New Zealand.

Consumptive and nonconsumptive effects of omnivorous tadpoles on aquatic invertebrate communities

AbstractConsumptive effects (CEs) of predation have been well‐studied in most aquatic systems, but nonconsumptive effects (NCEs) on prey have only recently received limited attention. As aquatic consumers, tadpoles have traditionally been considered strict herbivores, leaving their predatory impacts via CEs and NCEs largely unexplored. We quantified omnivory among wood frog (Lithobates sylvaticus) tadpoles and characterized their CEs and NCEs on invertebrate communities. Tadpoles from natural ponds were dissected to quantify the frequency of omnivory generally, as well as specifically in relation to pond size and tadpole morphology. Additional tadpoles were employed in a mesocosm experiment that manipulated tadpole presence (absent, caged, or free‐swimming) to quantify CEs and NCEs on freshwater zooplankton and macroinvertebrate communities. Over 70% of tadpoles in natural ponds engaged in omnivory, primarily on zooplankton, and tadpoles with wider heads and deeper tails were more likely to be omnivorous. Tadpoles in mesocosms exhibited CEs and NCEs on invertebrate communities, with stronger effects exerted on zooplankton than macroinvertebrates. The NCEs of tadpoles on invertebrates likely included production of predatory chemical cues that influenced invertebrate behavior, abundance, and community composition. Because tadpoles are often the dominant vertebrate predators in ephemeral aquatic ecosystems, this study stresses their ecological importance in structuring aquatic communities.

Assessing the Impact of Chemical Algae Management Strategies on Anurans and Aquatic Communities.

Pond management with chemical and biological agents that reduce overgrowth of algae is an important means of maintaining water quality in residential ponds, yet the effects on nontarget species are not fully understood. We assessed the impact of Aquashade (a common nontoxic pond dye) and copper sulfate (a toxic algaecide) on American toad (Anaxyrus americanus), northern leopard frog (Lithobates pipiens), and Cope's gray treefrog (Hyla chrysoscelis) metamorphosis in outdoor mesocosm experiments. We also evaluated the relative impact of tadpole grazing versus chemical treatment on phytoplankton and periphyton abundance. We found no significant effects of pond management treatment on anuran metamorphosis, suggesting that addition of Aquashade and copper sulfate at tested concentrations does not significantly impact anurans under these experimental conditions. Interestingly, we found that the presence of tadpoles more strongly reduced algal abundance than Aquashade or copper sulfate by significantly decreasing phytoplankton and periphyton abundance over time. The present study suggests that anuran tadpoles may be effective at maintaining water quality, and that Aquashade and copper sulfate may have minimal effects on amphibian metamorphosis. Environ Toxicol Chem 2023;42:213-224. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Amphibian loss alters periphyton structure and invertebrate growth in montane streams.

Amphibians are declining worldwide due to a combination of stressors such as climate change, invasive species, habitat loss, pollution and emergent diseases. Although their losses are likely to have important ecological consequences on the structure and functioning of freshwater ecosystems, this issue has been scarcely explored. We conducted an experiment in three montane streams-where primary production is the main source of energy and carbon-to assess the effects of amphibian disappearance (i.e. presence or absence of the common midwife toad Alytes obstetricans, a common species found in pools of these streams) on several aspects of ecosystem functioning and structure: periphyton biomass and chlorophyll a concentration, algal assemblage structure, and growth of macroinvertebrate grazers. We compared four types of experimental enclosures: (i) without macroinvertebrates or amphibians; (ii) with larvae of the caddisfly Allogamus laureatus; (iii) with A. obstetricans tadpoles; and (iv) with both A. laureatus larvae and A. obstetricans tadpoles. The absence of tadpoles increased periphyton biomass, but did not cause differences on inorganic sediment accrual. The algal assemblage had a higher diversity in the absence of tadpoles, and their characteristic taxa differed from the assemblages in presence of tadpoles. A. laureatus presented higher mass in presence of tadpoles; however, tadpole length was not affected by presence of macroinvertebrates. Our results suggest that presence of tadpoles is a driver of periphyton accrual and assemblage structure, acting as top-down control and with key potential consequences on the functioning of montane stream ecosystems.

Effects of elevated temperature, reduced hydroperiod, and invasive bullfrog larvae on pacific chorus frog larvae.

Climate change and invasive species threaten many ecosystems, including surface freshwater systems. Increasing temperatures and reduced hydroperiod due to climate change may promote the persistence of invasive species and facilitate new invasions due to potentially higher tolerance to environmental stress in successful invaders. Amphibians demonstrate high levels of plasticity in life history characteristics, particularly those species which inhabit both ephemeral and permanent water bodies. We tested the influence of two projected effects of climate change (increased temperature and reduced hydroperiod) on Pacific chorus frog (Pseudacris regilla) tadpoles alone and in combination with the presence of tadpoles of a wide-spread invasive amphibian, the American bullfrog (Lithobates catesbeianus). Specifically, we explored the effects of projected climate change and invasion on survival, growth, mass at stage 42, and development rate of Pacific chorus frogs. Direct and indirect interactions between the invasive tadpole and the native tadpole were controlled via a cage treatment and were included to account for differences in presence of the bullfrog compared to competition for food resources and other direct effects. Overall, bullfrogs had larger negative effects on Pacific chorus frogs than climate conditions. Under future climate conditions, Pacific chorus frogs developed faster and emerged heavier. Pacific chorus frog tadpoles developing in the presence of American bullfrogs, regardless of cage treatment, emerged lighter. When future climate conditions and presence of invasive American bullfrog tadpoles were combined, tadpoles grew less. However, no interaction was detected between climate conditions and bullfrog presence for mass, suggesting that tadpoles allocated energy towards mass rather than length under the combined stress treatment. The maintenance of overall body condition (smaller but heavier metamorphs) when future climate conditions overlap with bullfrog presence suggests that Pacific chorus frogs may be partially compensating for the negative effects of bullfrogs via increased allocation of energy towards mass. Strong plasticity, as demonstrated by Pacific chorus frog larvae in our study, may allow species to match the demands of new environments, including under future climate change.

Phenotypic Plasticity of Salamander Hatchlings in the Pre-Feeding Stage in Response to Future Prey.

Vulnerability of animals immediately after hatching may induce plasticity in early ontology that becomes important for subsequent survival and growth. Ezo salamanders (Hynobius retardatus) are amphibians inhabiting ponds in Hokkaido, Japan where ezo brown frogs (Rana pirica) spawn on occasion. The salamander larvae must achieve sufficient size in order to successfully capture frog tadpoles, and we examined whether the presence of tadpoles causes development of greater body and/or gape size in newly hatched salamander larvae, which will in turn result in advantageous future prey-predator interactions. To examine this hypothesis, we conducted three laboratory experiments to demonstrate the phenotypic plasticity of salamander hatchlings in response to the presence or absence of frog tadpoles and to screen the type of signals involved in the expression of the phenotypic plasticity. First, salamander hatchlings were reared alone or with tadpoles, and the growth and morphological traits of the hatchlings were compared. The results showed that hatchling larvae grew faster with a more developed gape in the presence of tadpoles. Next, to identify the type of signals inducing this plasticity, two separate experiments with manipulated chemical and visual signals from tadpoles were conducted. The findings showed that faster growth and a more developed gape were induced by chemical but not visual signals. This plasticity may be an adaptive strategy because it increases the likelihood of preying on tadpoles in future prey-predator interactions.

Aspects of the reproductive ecology of Trachycephalus cunauaru (Anura: Hylidae) in the southern Amazon

ABSTRACT Trachycephalus cunauaru is an Amazonian hylid that uses phytotelmata to reproduce. There is relatively little information about the species, mainly due to the difficulty of accessing their reproductive sites. In this study, we gathered data on the ecology and natural history of T. cunauaru in the southern Amazon, in the state of Mato Grosso, Brazil. In addition to natural phytotelmata, we used buckets installed at a height of 10 m as artificial phytotelmata. We compared physical and chemical characteristics, as well as the presence of tadpoles between natural and artificial phytotelmata. We also collected data on the reproductive behavior of the species through the use of camera traps. We recorded a density of 14.1 reproductive sites per km². Environmental parameters differed significantly between artificial and natural phytotelmata. In artificial sites, the presence of tadpoles was directly related to trees with a larger diameter. We registered oophagy for the first time for the species and observed that males can use more than one phytotelm. We also recorded the presence of snakes within the reproductive sites. We determined that artificial sites and digital camera traps are a satisfactory alternative for behavioral observations of T. cunauaru and possibly for other species with a similar habit.

A cross-sectional observational study investigating the association between sedges (swamp grasses, Cyperaceae) and the prevalence of immature malaria vectors in aquatic habitats along the shore of Lake Victoria, western Kenya

Background: Strategies that involve manipulations of the odour-orientation of gravid malaria vectors could lead to novel attract-and-kill interventions. Recent work has highlighted the potential involvement of graminoid plants in luring vectors to oviposition sites. This study aimed to analyse the association between water-indicating graminoid plants (Cyperaceae, sedges), other abiotic and biotic factors and the presence and abundance of early instar Anopheles larvae in aquatic habitats as a proxy indicator for oviposition. Methods: A cross-sectional survey of 110 aquatic habitats along the shores of Lake Victoria was done during the rainy season. Habitats were sampled for mosquito larvae using the sweep-net method and habitat characteristics recorded. Results: Anopheles arabiensis was the dominant species identified from aquatic habitats. Larvae of the secondary malaria vectors such as Anopheles coustani, An. rufipes and An. maculipalpis were found only in habitats covered with graminoids, whereas An. arabiensis, An. ziemanni and An. pharoensis were found in both habitats with and without graminoid plants. The hypothesis that sedges might be positively associated with the presence and abundance of early instar Anopheles larvae could not be confirmed. The dominant graminoid plants in the habitats were Panicum repens, Cynodon dactylon in the Poaceae family and Cyperus rotundus in the Cyperaceae family. All of these habitats supported abundant immature vector populations. The presence of early instar larvae was significantly and positively associated with swamp habitat types (OR=22, 95% CI=6-86, P<0.001) and abundance of late Anopheles larvae (OR=359, CI=33-3941, P<0.001), and negatively associated with the presence of tadpoles (OR=0.1, CI=0.0.01-0.5, P=0.008). Conclusions: Early instar malaria vectors were abundant in habitats densely vegetated with graminoid plants in the study area but no specific preference could be detected for any species or family. In search for oviposition cues, it might be useful to screen for chemical volatiles released from all dominant plant species.

A cross-sectional observational study investigating the association between sedges (swamp grasses, Cyperaceae) and the prevalence of immature malaria vectors in aquatic habitats along the shore of Lake Victoria, western Kenya

Background: Strategies that involve manipulations of the odour-orientation of gravid malaria vectors could lead to novel attract-and-kill interventions. Recent work has highlighted the potential involvement of graminoid plants in luring vectors to oviposition sites. This study aimed to analyse the association between water-indicating graminoid plants (Cyperaceae, sedges), other abiotic and biotic factors and the presence and abundance of early instar Anopheles larvae in aquatic habitats as a proxy indicator for oviposition. Methods: A cross-sectional survey of 110 aquatic habitats along the shores of Lake Victoria was done during the rainy season. Habitats were sampled for mosquito larvae using the sweep-net method and habitat characteristics recorded. Results: Anopheles arabiensis was the dominant species identified from aquatic habitats. Larvae of the secondary malaria vectors such as Anopheles coustani, An. rufipes and An. maculipalpis were found only in habitats covered with graminoids, whereas An. arabiensis, An. ziemanni and An. pharoensis were found in both habitats with and without graminoid plants. The hypothesis that sedges might be positively associated with the presence and abundance of early instar Anopheles larvae could not be confirmed. The dominant graminoid plants in the habitats were Panicum repens, Cynodon dactylon in the Poaceae family and Cyperus rotundus in the Cyperaceae family. All of these habitats supported abundant immature vector populations. The presence of early instar larvae was significantly and positively associated with swamp habitat types (OR=22, 95% CI=6-86, P<0.001) and abundance of late Anopheles larvae (OR=359, CI=33-3941, P<0.001), and negatively associated with the presence of tadpoles (OR=0.1, CI=0.0.01-0.5, P=0.008). Conclusions: Early instar malaria vectors were abundant in habitats densely vegetated with graminoid plants in the study area but no specific preference could be detected for any species or family. In search for oviposition cues, it might be useful to screen for chemical volatiles released from all dominant plant species.

Field trials of chemical suppression of embryonic cane toads (Rhinella marina) by older conspecifics.

Laboratory experiments have shown that the viability of embryos of the invasive cane toad (Rhinella marina) can be reduced by exposure to chemical cues from older conspecific larvae. These effects (very strong in laboratory trials) may offer an exciting new approach to controlling this problematic invasive species in Australia. However, the degree to which the method works in natural environments has yet to be assessed.Our experiments in the laboratory and in seminatural outdoor waterbodies show that chemical cues from tadpoles do indeed suppress the growth, development, and survival of conspecific larvae that are exposed as embryos and do so in a dose‐dependent manner; higher tadpole densities cause greater suppression of embryos.In seminatural outdoor waterbodies, suppressor‐exposed tadpoles were less than half as likely to survive to metamorphosis as were controls, and were much smaller when they did so and hence, less likely to survive the metamorph stage. Additionally, female cane toads were less likely to oviposit in a waterbody containing free‐ranging (but not cage‐enclosed) tadpoles, suggesting that the presence of tadpoles (rather than the chemical cues they produce) may discourage oviposition.Broadly, our results suggest that the suppression effect documented in laboratory studies does indeed occur in the field also, and hence that we may be able to translate that approach to develop new and more effective ways to reduce rates of recruitment of peri‐urban populations of cane toads in their invasive range.

A cross-sectional observational study investigating the association between sedges (swamp grasses, Cyperaceae) and the prevalence of immature malaria vectors in aquatic habitats along the shore of Lake Victoria, western Kenya.

Background: Strategies that involve manipulations of the odour-orientation of gravid malaria vectors could lead to novel attract-and-kill interventions. Recent work has highlighted the potential involvement of graminoid plants in luring vectors to oviposition sites. This study aimed to analyse the association between water-indicating graminoid plants (Cyperaceae, sedges), other abiotic and biotic factors and the presence and abundance of early instar Anopheles larvae in aquatic habitats as a proxy indicator for oviposition. Methods: A cross-sectional survey of 110 aquatic habitats along the shores of Lake Victoria was done during the rainy season. Habitats were sampled for mosquito larvae using the sweep-net method and habitat characteristics recorded. Results: Anopheles arabiensis was the dominant species identified from aquatic habitats. Larvae of the secondary malaria vectors such as Anopheles coustani, An. rufipes and An. maculipalpis were found only in habitats covered with graminoids, whereas An. arabiensis, An. ziemanni and An. pharoensis were found in both habitats with and without graminoid plants. The hypothesis that sedges might be positively associated with the presence and abundance of early instar Anopheles larvae could not be confirmed. The dominant graminoid plants in the habitats were Panicum repens, Cynodon dactylon in the Poaceae family and Cyperus rotundus in the Cyperaceae family. All of these habitats supported abundant immature vector populations. The presence of early instar larvae was significantly and positively associated with swamp habitat types (OR=22, 95% CI=6-86, P<0.001) and abundance of late Anopheles larvae (OR=359, CI=33-3941, P<0.001), whilst the association was negative with tadpole presence (OR=0.1, CI=0.0.01-0.5, P=0.008). Conclusions: Early instar malaria vectors were abundant in habitats densely vegetated with graminoid plants in the study area but specific preference for any of the graminoids could not be detected. In search for oviposition cues, it might be useful to screen for chemical volatiles released from all dominant plant species.

Assessing water conditions for Heleophryne rosei tadpoles and the conservation relevance

The Table Mountain Ghost Frog (Heleophryne rosei) is endemic to the Table Mountain massif and is Critically Endangered. Other than clear, clean perennial stream flow, the optimal aquatic conditions required by their larvae are unknown. Dissolved oxygen, temperature, pH, electro-conductivity, aspect and permanence of flow are the independent variables measured seasonally at two sampling altitudes at 12 rivers of the massif. Using a logistic regression model we found that a permanence of water flow and lower water temperature were significant predictors of tadpole presence. Streams with mean summer temperature above 17.2 °C, at 300 m – 400 m above sea level, do not have tadpoles. Summer and autumn abstraction should be avoided, while a summer water temperature above an average of 17.2 °C is a threshold of potential concern for management authorities responsible for biodiversity conservation, threat mitigation efforts, and bulk-water supply and abstraction.Conservation implications: The Environmental Water Reserve has not been determined for streams of Table Mountain. The requirements of the Critically Endangered Table Mountain Ghost Frog (Heleophryne rosei) can be adopted as the minimum conditions to support this species and associated communities. Perennial flow, an average January water temperature of 17.2 °C or lower.

The distribution and status of the Giant Burrowing Frog Heleioporus australiacus in the Shoalhaven region of south-eastern New South Wales

Surveys were conducted for the Giant Burrowing Frog Heleioporus australiacus within 50 km of Nowra, on the south coast of New South Wales using a variety of methods. Thirty-eight 250 m transects were surveyed at night for 30 min each and 0–12 adult frogs were detected during these searches. Additional diurnal searches for tadpoles proved to be the most efficient method to detect the species and locate breeding sites. Of 102 sites surveyed, fragmented populations were found at 27 by the presence of tadpoles and adult frogs. The vegetation at these sites was woodland and open forest with a dense shrublayer of heath, but was often ecotonal. Forty-six percent of the sites were within 100 m of cliff edges/waterfalls. The lithology of sites where the frog was found varied from Hawkesbury, Nowra and Snapper Point sandstones. The exception was a population south of Ulladulla that occurs on undifferentiated sediments, but at that site exposed sandstone and a sandy overlay was present. The location of tadpoles indicated that adults were highly selective of the section of drainage line used for breeding. Often these sites consisted of a few small pools in non-perennial creeks. Breeding behaviour was associated with late summer and autumn rain, but in some sites reproduction did not occur annually. Based on distribution and habitat preference, the region has five discrete populations. Urban development has fragmented populations.

Benefits and limits of comparative effectiveness studies in evidence-based conservation

Conservation action aims at halting the erosion of biodiversity. Assessing the outcome of a conservation intervention is thus key to improving its efficiency. This is often done by comparing an intervention to a control. Comparative effectiveness studies, on the other hand, compare multiple conservation interventions among each other. In doing so, one can determine which are the most beneficial interventions despite the lack of a control and a formal experimental design. We use an amphibian conservation study to discuss the benefits and limits of this approach. We used the comparative effectiveness approach to evaluate the outcome of a pond creation project. We measured habitat variables at three spatial scales (pond, terrestrial microhabitat, and landscape) and used multistate occupancy and N-mixture models to account for imperfect detection and to relate the explanatory variables to pond colonization, species abundance and the presence of tadpoles (i.e., evidence for successful reproduction). Although characteristics of the created ponds mattered, the availability of suitable terrestrial microhabitat (such as dry stone walls) was even more important in terms of conservation success as measured by colonization and abundance. This case study shows that successful amphibian conservation action depends on landscape complementation, i.e., the paired availability of suitable aquatic and terrestrial microhabitat. We conclude that comparative effectiveness studies can be used to provide critical information for improved conservation action. However, small sample size and a lack of randomization may a priori represent an impediment to strong inference. Nevertheless, comparative effectiveness studies can provide valuable guidance for evidence-based conservation.

Selectividad de los renacuajos de Incilius valliceps (Anura: Bufonidae) sobre el zooplancton de agua dulce

The dietary preferences of tropical tadpoles and the way they interact with zooplankton often go unstudied in aquatic ecosystems. Goals. We investigated the interactions between Incilius valliceps tadpoles and a freshwater zooplankton community found in an artificial aquatic pond located on Cozumel Island in Quintana Roo, Mexico. Methods. We determined zooplankton abundance, richness, the Shannon-Wiener diversity index, and the proportion of each zooplankton species in the environment. We also evaluated characteristics of the tadpole population such as body size, abundance, and proportion of prey ingested as determined by stomach content analysis. We used the Jacobs selectivity index to determine tadpole prey of preference. Results. The rotifers Anuraeopsis fissa and an unidentified species of Bdelloidea group were dominant among the eight zooplankton species consumed. The selectivity index showed that I. valliceps tadpoles preferred to consume macro-zooplankton (ostracods and cladocerans) instead of the rotifer species available. Tadpoles positively chose Cypridopsis vidua throughout their growth and development and Moina wierzejskii during their early developmental stages, and negatively selected the rotifer species of the one unidentified species of Bdelloidea, A. fissa, and Epiphanes brachionus. In the presence of tadpoles, Keratella americana, Lepadella patella, and Lecane luna were either present in extremely low abundances or not found in the aquatic community, and M. wierzejskii produced males and resistant eggs. Conclusions. The findings of this study clarify the dietary needs of tropical tadpoles and their role in aquatic ecosystems.

Induced parental care in a poison frog: a tadpole cross-fostering experiment.

ABSTRACTUnderstanding the external stimuli and natural contexts that elicit complex behaviours, such as parental care, is key in linking behavioural mechanisms to their real-life function. Poison frogs provide obligate parental care by shuttling their tadpoles from terrestrial clutches to aquatic nurseries, but little is known about the proximate mechanisms that control these behaviours. In this study, we used Allobates femoralis, a poison frog with predominantly male parental care, to investigate whether tadpole transport can be induced in both sexes by transferring unrelated tadpoles to the backs of adults in the field. Specifically, we asked whether the presence of tadpoles on an adult's back can override the decision-making rules preceding tadpole pick-up and induce the recall of spatial memory necessary for finding tadpole deposition sites. We used telemetry to facilitate accurate tracking of individual frogs and spatial analysis to compare movement trajectories. All tested individuals transported their foster-tadpoles to water pools outside their home area. Contrary to our expectation, we found no sex difference in the likelihood to transport or in the spatial accuracy of finding tadpole deposition sites. We reveal that a stereotypical cascade of parental behaviours that naturally involves sex-specific offspring recognition strategies and the use of spatial memory can be manipulated by experimental placement of unrelated tadpoles on adult frogs. As individuals remained inside their home area when only the jelly from tadpole-containing clutches was brushed on the back, we speculate that tactile rather than chemical stimuli trigger these parental behaviours.

Feeding Habits of Two Sympatric Rocket Frogs (Genus Ptychadena) in a Forest Remnant of Southern-Central Ivory Coast, West Africa

The decline of tropical amphibian species calls for studies on their biology and ecology, in order to understand their role in the respective ecosystems. We studied the diet of Ptychadena oxyrhynchus and P. longirostris, two rocket frogs co-occurring along dirt roads with puddles in the Azagny National Park, southern-central Ivory Coast. Stomach contents of 62 individuals of P. oxyrhynchus and 75 specimens of P. longirostris were obtained using the stomach-flushing method. The diet of both species was essentially characterized by various terrestrial invertebrates (predominantly insects) and both species can be considered opportunistic feeders. The presence of tadpoles in the stomach of a female P. longirostris indicates that this species may occasionally prey on aquatic food items as well. The large overlap in prey between both study species can be taken as a hint that competition for food does not play a major role between them. An unexpected observation was the proportion of plant fragments in the diet of our frogs. However, it remains unknown if they devoured plant deliberately or not. Future research should investigate this question.

The distribution of the Red-crowned Toadlet Pseudophryne australis in the Nepean-Burragorang region of the Sydney Basin

Surveys were conducted for the Red-crowned Toadlet Pseudophryne australis in Burragorang State Conservation Area (SCA), Nattai National Park (NP), Thirlmere Lakes NP and the Upper Nepean SCA west of Sydney, New South Wales using a variety of methods. Scattered populations of Pseudophryne australis were detected by the presence of tadpoles and calling males in a range of vegetation communities. These communities included escarpment grey gum forest, exposed Burragorang sandstone shrub woodland, Nattai sandstone dry shrub forest, sheltered sandstone intermediate blue gum forest and Nepean gorge moist forest. All detections were within non-perennial creeks on Hawkesbury or Mittagong sandstones or enriched soils derived from these sandstones. The number of calling frogs at sites ranged from one to about 400. Nine 250 m transects were surveyed at night for 30 min each and 0–36 adult frogs were detected during these searches. Diurnal searches were conducted for tadpoles and adult frogs by using the ‘shout’ metho...

Toxicity of Vertimec® 18 EC (active ingredient abamectin) to the neotropical cladoceran Ceriodaphnia silvestrii

The aim of the present study was to evaluate the toxicity of abamectin to the neotropical cladoceran Ceriodaphnia silvestrii. To this end, acute and chronic bioassays were conducted with the commercial formulation Vertimec® 18 EC. In addition, the toxicity of water samples taken from a microcosm experiment evaluating the effects of a single application (144μga.i./L) and two applications (2×36μga.i./L) of Vertimec® 18 EC, in the presence or absence of a tadpole species (Lithobates catesbeianus), was also assessed. The acute LC50-48h for immobilization was 1.47μga.i./L and chronic NOEC-8d for survival and fertility (number of neonates per female) were 169 and 84nga.i./L, respectively. Irrespective of the presence of tadpoles, water samples from the microcosms applied with the single concentration of 144μga.i./L remained toxic until the end of the experiment, even when samples were diluted 32 times with culture medium. Water in the repeated pesticide treatment showed a similar toxic response after both applications. Toxicity of water samples from the microcosms was lower than that expected based on the generated LC50 values, which is explained by a potential reduced bioavailability of the test compound resulting from absorbance to organic material. Potential side-effects on C. silvestrii related with the use of Vertimec® 18 EC in Brazil and the suitability of this species for tropical toxicity testing are discussed.

Pseudacris regilla tadpole density differentially affects periphyton and macrophytes in a California vernal pool community

Biotic interactions between herbivores and primary producers are believed to play a major role in determining community composition of many ecological communities. How differences in herbivore abundance alter the relative importance of these interactions is not well understood, especially in seasonal wetland systems. This study investigated the effects of varying Pseudacris regilla (pacific chorus frog) larval densities on California vernal pool aquatic communities. It was hypothesized that with increasing tadpole density, macrophyte percent cover, biomass, diversity, and richness would decrease; while algae and zooplankton abundance, biomass and richness increase. The experimental mesocosm design consisted of five tadpole density treatments, and was arranged in a 5×5 randomized block design. Each density treatment was replicated five times. Macrophytes, algae and invertebrates were identified to the lowest possible taxonomic unit, and the biomasses of each community were quantified. Treatment effects were determined using both multivariate and univariate analysis of variance techniques. To detect differences in community composition, multivariate ordination analyses (ANOSIM, SIMPER, NMDS) were conducted. Increasing densities of P. regilla tadpoles had significant effects on the vernal pool macrophyte community. Plant diversity, species richness, biomass, and percent cover were all negatively affected by increasing tadpole densities. Macrophyte community structure was also found to be significantly different in the presence of tadpoles due to the fact that Downingia bicornuta, Ranunculus aquatilis, and Gratiola ebracteata were predominately isolated to mesocosms were P. regilla was absent. In addition, periphyton biomass was shown to be facilitated by increasing tadpole densities in the lower treatment ranges. Aquatic macroinvertebrates and phytoplankton communities, on the other hand, were not significantly affected by increasing tadpole densities. This study demonstrates the influence of P. regilla larvae on the primary producers within California vernal pool systems. Understanding the effects of these abundant consumers, and the mechanisms that drive the importance of their direct and indirect effects are essential for the conservation of vernal pools and the threatened species associated with them.