Amphibians and agricultural chemicals: Review of the risks in a complex environment

https://groups.nceas.ucsb.edu/trn/background-reading/Hamer-McDonnell2008.pdf/at_download/file

Amphibian ecology and conservation in the urbanising world: A review

In organisms with complex life cycles, physiological stressors during early life stages may have fitness-level impacts that are delayed into later stages or habitats. We tested the hypothesis that body size and date of metamorphosis, which are highly responsive to aquatic stressors, influence post-metamorphic survival and movement patterns in the terrestrial phase of an ephemeral pond-breeding frog by examining these traits in two populations of northern red-legged frogs (Rana aurora aurora). To increase variation of body size at metamorphosis, we manipulated food availability for 314 of 1045 uniquely marked tadpoles and estimated the probability that frogs survived and emigrated using concentric rings of drift fencing surrounding ponds and Bayesian capture–recapture modeling. The odds of surviving and emigrating from the ponds to the innermost drift fences, ∼12 m, increased by factors of 2.20 (95% credibility intervals 1.39–4.23) and 2.54 (0.94– 4.91) with each millimeter increase in snout–vent length an...

Carryover Aquatic Effects On Survival Of Metamorphic Frogs During Pond Emigration

Ecologists have long realized that stable species richness values can mask rapid turnover in species composition. Because turnover occurs as a consequence of both local and regional processes, understanding the responsible factors provides insight on processes influencing community structure at different scales. Despite the insights to be gained from data on species turnover, they remain relatively uncommon. We present data on the interannual turnover in species composition of larval amphibian communities in 37 ponds over seven years. Species composition of a given pond community was highly dynamic; about half of the species that could be found breeding in a particular pond were actually present in a given year. All species participated in this community turnover, but to different degrees. Using a model selection approach, we show that a statistical model including local environmental factors (pond area, hydroperiod, and canopy cover) and pond connectivity on the landscape provided the best predictions of turnover. Averaged parameter estimates were significant for area, hydroperiod, and connectivity and these same variables were identified by hierarchical partitioning as having significant independent effects on turnover. Area and hydroperiod were negatively related to turnover, whereas connectivity was positively related to turnover. Additionally, the average fraction of years a species was present in a pond was positively correlated with average local population size, but even more strongly correlated with regional population size, suggesting both local and regional influences on turnover. Of the measured biotic factors (biomass of fish, invertebrate predators, anuran and caudate larvae), presence of fish was the only factor that significantly affected rates of turnover. Several mechanism could be responsible for changes in species composition (species extinctions, skipped breeding and movement of choruses), but extinctions appear to be the major cause of turnover. These results have important implications to understanding long-term persistence of species on landscapes and the causes of patterns in species richness on environmental gradients.

/pdf/turnover-in-an-amphibian-metacommunity-the-role-of-local-and-3gro60m1n7.pdf

Turnover in an amphibian metacommunity : the role of local and regional factors

Movement ecology of amphibians: A missing component for understanding population declines

Research on amphibian movement patterns can aid in strengthening amphibian conservation strategies. Yet for many species, there remain substantial gaps in our knowledge of such movement patterns. From 1999–2002, we documented movement patterns to and from breeding pools of both adult and juvenile Rana sylvatica LeConte (Wood Frog) and Ambystoma maculatum Shaw (Spotted Salamander) by using drift fence arrays at three restored vernal pools in Maine to lend insight into conservation strategies for these two species. Adults and juveniles of both species exhibited nonrandom movement at breeding pools directed preferentially from and toward closed-canopy forested habitat. Marked male, female, and juvenile R. sylvatica were recaptured at 30 m, 150 m, and 300 m from the pool in the surrounding terrestrial environment. Most terrestrial recaptures occurred within the forested wetland habitat to the north of the pool. Median snout–vent lengths (SVL) of recaptured juvenile R. sylvatica were progressively lar...

Movement Patterns of Adult and Juvenile Rana sylvatica (LeConte) and Ambystoma maculatum (Shaw) in Three Restored Seasonal Pools in Maine

Assessing the success of created seasonal pools as mitigation for the loss of wooded wetlands is generally based on two or three years of monitoring. We monitored a wetland mitigation site in midcoast Maine, USA, from 1999 to 2004 to track populations of wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum) in three created seasonal pools. Our goal was to study breeding patterns for six years to assess if presence of breeding animals in the first three years corresponded with long-term reproductive success and to track changes in vegetation development and hydrology in the mitigated pools. Breeding effort (egg masses/female) and reproductive success (juveniles/egg mass) were assessed using full enclosure drift fence/pitfall trap arrays and egg mass counts. Breeding effort was similar in all three pools for both species. However, for wood frogs, reproductive success was inversely related to hydroperiod and highest in the single pool that successfully replicated the desired seasonal water regime. The other two pools developed permanent and semi-permanent hydroperiods, thereby supporting populations of green frogs (Rana clamitans). Green frog tadpoles within these pools preyed upon wood frog eggs and embryos, causing almost complete losses in the last four years of the study. While spotted salamander reproductive success was also reduced in the permanent pool, spotted salamanders were more successful at producing metamorphs in the presence of green frogs. Over the study period, common cattail (Typha latifolia) dominated the pools, and although wetland vegetation did develop, it was not typical of forested seasonal pools. Our work shows that the presence of breeding amphibians characteristic of seasonal pools in the first three years is not sufficient to determine reproductive success of target species in created pools. Hydrology and canopy cover are elements of critical concern if created pools are to support native amphibian communities associated with seasonal pools.

http://www.wle.umaine.edu/MaineLeap/Vasconcelos%20and%20Calhoun%202006%20-%20created%20seasonal%20pools.pdf

Daniel Vasconcelos

Papers

Movement Patterns of Adult and Juvenile Rana sylvatica (LeConte) and Ambystoma maculatum (Shaw) in Three Restored Seasonal Pools in Maine

Monitoring created seasonal pools for functional success: A six-year case study of amphibian responses, Sears Island, Maine, USA