Collaborative Research: Land-Use Practices And Persistence Of Amphibian Populations

Over the past 200 years, conversion of land for agricultural use, industrial development, and urban sprawl has drastically reduced natural habitat for many species and is considered the most serious threat to biological diversity. Fragmentation divides once continuous natural habitats into smaller pieces that are often separated by areas unsuitable to sustain viable populations. The goal of the proposed research is to understand how important local population and metapopulation processes are altered by fragmentation of natural habitats in a model system of pond-breeding amphibians. The primary objectives of the proposed study are to experimentally compare demographic and behavioral responses of amphibians in clear-cut (with and without coarse woody debris), partial-cut, edge, and intact forest habitats around replicated natural breeding ponds. These results will lead to a better understanding of the habitat requirements for successful recruitment and survival of local populations, and how amphibians disperse through fragmented landscapes. It will allow strong inferences about the disruption of metapopulation dynamics in amphibians caused by fragmentation and about how to prevent population declines and extinctions. Further, information from this project is essential to the development of conservation and management plans in state natural resource agencies, the U.S.D.A. Forest Service, and the Bureau of Land Management

Collaborative Research: Land-Use Practices And Persistence Of Amphibian Populations.

Over the past 200 years, conversion of land for agricultural use, industrial development, and urban sprawl has drastically reduced natural habitat for many species and is considered the most serious threat to biological diversity. Fragmentation divides once continuous natural habitats into smaller pieces that are often separated by areas unsuitable to sustain viable populations. The goal of the proposed research is to understand how important local population and metapopulation processes are altered by fragmentation of natural habitats in a model system of pond-breeding amphibians. The primary objectives of the proposed study are to experimentally compare demographic and behavioral responses of amphibians in clear-cut (with and without coarse woody debris), partial-cut, edge, and intact forest habitats around replicated natural breeding ponds. These results will lead to a better understanding of the habitat requirements for successful recruitment and survival of local populations, and how amphibians disperse through fragmented landscapes. It will allow strong inferences about the disruption of metapopulation dynamics in amphibians caused by fragmentation and about how to prevent population declines and extinctions. Further, information from this project is essential to the development of conservation and management plans in state natural resource agencies, the U.S.D.A. Forest Service, and the Bureau of Land Management

Clearcutting has a long-lasting effect on habitat connectivity for a forest amphibian by decreasing permeability to juvenile movements

Conservation of forest amphibians is dependent on finding the right balance between management for timber production and meeting species\u27 habitat requirements. For many pond-breeding amphibians, successful dispersal of the juvenile stage is essential for long-term population persistence. We investigated the influence of timber-harvesting practices on the movements of juvenile wood frogs (Lithobates sylvaticus). We used a chronosequence of stands produced by clear-cutting to evaluate how stand age affects habitat permeability to movements. We conducted experimental releases of juveniles in 2008 (n = 350) and 2009 (n = 528) in unidirectional runways in four treatments: mature forest, recent clearcut, 11-year-old, and 20-year-old regeneration. The runways were 50 x 2.5-m enclosures extending into each treatment, perpendicular to a distinct edge, with four tracking stations at 10, 20, 30, and 40 m from the edge. We recorded the number of animals reaching each tracking station, and the proportion of animals changing their direction of movement at each distance. We found that the mature forest was 3.1 and 3.7 times more permeable than the 11-year-old regeneration and the recent clearcut, respectively. Animals actively avoided open-canopy habitats and sharp edges; significantly more animals returned toward the closed-canopy forest at 0 m and 10 m in the less permeable treatments. There were no significant differences in habitat permeability between the mature forest and the 20-year-old regeneration. Our study is the first to directly assess habitat permeability to juvenile amphibian movement in relation to various forestry practices. We argue that habitat permeability at this scale is largely driven by the behavior of animals in relation to habitat disturbance and that caution needs to be used when using spatial modeling and expert-derived permeability values to assess connectivity of amphibian populations. The effects of clear-cutting on the migratory success of juvenile L. sylvaticus are long-lasting. Forestry practices that involve canopy removal and conversion of natural forest to conifer plantations may affect regional population viability by hindering successful dispersal

Movement in the matrix: Substrates and distance to forest edge affect postmetamorphic movements of a forest amphibian

Population persistence often depends on functional connectivity for animals that transit multiple vegetation types to acquire resources, particularly for dispersers navigating a landscape matrix fragmented by agriculture, forestry, or urbanization. For many pool-breeding amphibians, population viability depends on the ability of juveniles to locate and reach suitable habitat in the terrestrial matrix. Thus, identifying the scale and orientation of movements is necessary to predict the consequences of landscape configuration for populations. We conducted three experiments to evaluate if different vegetation types alter the behavior of post-metamorphic wood frogs (Lithobates sylvaticus). We measured the: (1) fine-scale movement (velocity, latency, path length, net displacement, path tortuosity, and orientation) of individuals (n = 150) released on five substrates (asphalt, corn, forest leaf litter, hay, lawn); (2) directionality of frogs (n = 168) released at different distances from forest in two open-cover types (lawns, hayfields); and (3) willingness of frogs (n = 240) to enter three land-cover types (asphalt, lawn, forest) when released within artificial refugia islands at different distances from forest. Using fluorescent powder, we mapped 318 movement paths and performance differed. Frogs demonstrated straighter paths, and greater net movements, path lengths, and velocities through treatments with lower structural complexity (asphalt \u3e lawn \u3e corn \u3e forest leaf litter \u3e hay). Frogs also exhibited forest-oriented directionality in asphalt, lawn, and corn but random orientation in forest control and hay. The willingness of individuals to leave a refugia island was lowest on asphalt (12% of released frogs), moderate on lawn (40%), and very high in forest (90%). Overall, results indicate that the quality of nonforest matrix may influence the ability of frogs to traverse open cover and orient toward forest from distances of ≥40–55 m. Thus, it is inaccurate to assume movement performance is uniform across all open-matrix types, an important distinction because many landscape-population models use expert-based values that are a one-size- fits- all measure for open cover. Our study provides field-based, mechanistic approximations of juvenile movement that can be useful for predicting how matrix composition and configuration might be managed to maintain or restore functional connectivity

Different open-canopy vegetation types affect matrix permeability for a dispersing forest amphibian

Population viability often depends on conserving functional connectivity in fragmented landscapes. For pool-breeding amphibians, population connectivity is largely maintained through juvenile dispersal, often through various vegetation types that may differ as filters or conduits to movement. We quantified the relative permeability of different types of open-canopy vegetation to juvenile wood frogs Lithobates sylvaticus to determine whether this influences functional connectivity during dispersal. We conducted experimental releases of juveniles (n = 561) in ten runways representing five treatments: hayfield, moderate-cover lawn (45–85% cover), open lawn (0% cover), row crop (forage-corn) and recent clear-cut. Runways consisted of 35 × 2·5 m enclosures, located perpendicular to a forest edge and extending into treatment areas with tracking stations at 10, 20 and 30 m. As indices of permeability, we measured the number of animals traversing each station, the proportion changing direction, movement timing and movement rates. Based on an index that compounds four metrics and scales them relative to mature forest as a control, permeability varied between open-canopy cover types in the following order: row crop \u3c hayfield \u3c clear-cut \u3c open lawn \u3c moderate-cover lawn. The highest proportions of individuals changed direction (towards forest) in the hayfield, moderate-cover lawn and clear-cut, suggesting that juveniles may make forays into the open and subsequently assess habitat. Nonetheless, individuals could eventually transit entire runways, indicated by overall recaptures at 30 m (e.g. hayfield, 29%; moderate-cover lawn, 24%; and clear-cut, 20%) at the end of our six-week experiment. Synthesis and applications. We provide quantitative evidence that open-canopy cover types may act as differential ecological filters to ranging movements, and ultimately dispersal. Differences in the willingness of animals to enter treatments, coupled with motility and residency times, support the differing roles of open-canopy vegetation as both filters and conduits to movement. Thus, it may be overly simplistic to estimate matrix permeability as uniformly low in models that predict movement in fragmented landscapes. To promote functional connectivity, modification of vegetation composition and configuration may provide an underutilized tool for conservation practitioners to reduce the effective isolation of habitat patches for post-metamorphic amphibians

Comparing relative abundance of amphibians in forest canopy gaps of natural origin vs. timber harvest origin

Relative abundance of amphibians in forest canopy gaps of natural origin vs. timber harvest origin.— Small–scale canopy gaps created by logging may retain adequate habitat structure to maintain amphibian abundance. We used pitfalls with drift fences to measure relative abundance of amphibians in 44 harvested gaps, 19 natural treefall gaps, and 36 closed–canopy forest plots. Metamorphs had relatively lower capture rates in large harvest gaps for Ambystoma maculatum, Lithobates catesbeianus, L. clamitans, and L. sylvaticus but we did not detect statistically significant (p \u3c 0.1) differences among gap types for Lithobates palustris metamorphs. L. clamitans juveniles and L. sylvaticus juveniles and adults had relatively lower capture rates in large harvest gaps. For juvenile–adult A. maculatum, we caught relatively fewer individuals in all gap types than in closed–canopy areas. Some groups with overall lower capture rates (immature Plethodon cinereus, juvenile L. palustris) had mixed differences among gap types, and Notophthalmus viridescens (efts) and adult P. cinereus showed no differences among gap types. One species, L. clamitans, was captured more often at gap edges than gap centers. These results suggest that harvest gaps, especially small gaps, provided habitat similar to natural gaps for some, but not all, amphibian species or life–stages

A multi-scale assessment of amphibian habitat selection: Wood frog response to timber harvesting

To understand changes in habitat selection in response to timber harvesting, we used radio-telemetry data from 82 adult wood frogs (Lithobates sylvaticus, formerly Rana sylvatica) and logistic regression modelling to assess habitat selection in response to an unharvested control and 3 forest management techniques: clearcutting (with removal of all merchantable timber \u3e 10 cm diameter), clearcutting with coarse woody debris (CWD) retention, and partial harvesting with retention of ∼50% canopy cover. At the home range scale, frogs selected the partially harvested treatment in spring 2005 and avoided the CWD-retained treatment in fall 2006. Frogs spent 5 ± 2 d (mean ± SE) longer in forested treatments than in both clearcut treatments, but certain individuals were able to specialize on the clearcut treatments. At the weekly activity centre scale, the best-supported models indicated that frogs were more likely to occupy locations with more complex ground structure, especially coarse woody debris, warmer temperatures, moister substrates, and greater canopy cover than random. Resource use among frogs overlapped substantially at both the weekly activity centre and daily microhabitat scales. Frogs selected daily microhabitats with more complex ground structure, greater canopy cover, and moister substrates than random. Selection at coarser scales may be mechanistically linked to finer scale resource selection by the physiological processes of thermoand hydro-regulation. Our results support recommendations for minimizing the impact of logging by retaining coarse woody debris in clearcuts and partial harvesting with retention of ∼50% canopy cover