James P. Gibbs

Importance of small wetlands for the persistence of local populations of wetland-associated animals

I simulated loss of small, legally unprotected freshwater wetlands in a 600 km2 area of Maine, USA to examine how loss of small wetlands altered the geometry of the wetland mosaic and thereby might affect the dynamics of metapopulations of wetland-associated organisms. Loss of small wetlands resulted in total wetland area declining by 19% (from 2032 to 1655 ha), total wetland number declining by 62% (from 354 to 136 wetlands), and average inter-wetland distance increasing by 67% (from 0.6 to 1.0 km). Also, average upland-wetland proximity decreased by 50% (0.5 to 1.0 km), such that just 54% of the landscape was within the maximum migration distance (1000m) of terrestrial-dwelling and aquatic-breeding amphibians after loss of small wetlands, versus 90% before loss. A spatially-structured demographic model revealed that local populations of turtles, small birds, and small mammals, stable under conditions of no wetland loss, faced a significant risk of extinction (P > 5%) after loss of small wetlands. No change in metapopulation extinction risk was evident for salamanders or frogs, largely because high rates of population increase buffered these taxa against local extinction. These results suggest that small wetlands play a greater role in the metapopulation dynamics of certain taxa of wetland animals than the modest area comprised by small wetlands might imply.

Amphibian Movements in Response to Forest Edges, Roads, and Streambeds in Southern New England

If management of landscape linkages is to be promoted as a means of conserving amphibian populations, it must be demonstrated that amphibian dispersal does not occur independently of ecosystem edges and other salient landscape features. I used drift fences and pitfall traps to intercept dispersing amphibians and examine amphibian movements relative to roads, forest edges, and streambeds in a forest tract in southern Connecticut. Capture rates of 3 species (marbled salamander, Ambystoma opacum; red-spotted newt, Notophthalmus viridescens; pickerel frog, Rana palustris) were influenced by forest borders and streambeds, whereas captures of 3 other species (spotted salamander, Ambystoma maculatum; redback salamander, Pleth-odon cinereus; wood frog, R. sylvatica) were not. Across all species, the relative permeability of forest-road edges was much reduced in comparison to the forest interior and to edges between forest and open land. The data suggest that landscape-level conservation strategies aimed at amphibians should account for such filters and conduits to amphibian movement.

IMPACTS OF ROAD DEICING SALT ON THE DEMOGRAPHY OF VERNAL POOL-BREEDING AMPHIBIANS

Deicing agents, primarily road salt, are applied to roads in 26 states in the United States and in a number of European countries, yet the scale of impacts of road salt on aquatic organisms remains largely under-studied. The issue is germane to amphibian conservation because both adult and larval amphibians are known to be particularly sensitive to changes in their osmolar environments. In this study, we combined survey, experimental, and demographic modeling approaches to evaluate the possible effects of road salt on two common vernal-pond-breeding amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica). We found that in the Adirondack Mountain Region of New York (USA), road salt traveled up to 172 m from the highway into wetlands. Surveys showed that egg mass densities of spotted salamanders (A. maculatum) and wood frogs (R. sylvatica) were two times higher in forest pools than roadside pools, but this pattern was better explained by road proximity than by increased salinity. Experiments demonstrated that embryonic and larval survival were reduced at moderate (500 muS) and high conductivities (3000 muS) in A. maculatum and at high conductivities in R. sylvatica. Demographic models suggest that such egg and larval stage effects of salt may have important impacts on populations near roads, particularly in the case of A. maculatum, for which salt exposure may lead to local extinction. For both species, the effect of road salt was dependent upon the strength of larval density dependence and declined rapidly with distance from the roadside, with the greatest negative effects being limited to within 50 m. Based on this evidence, we argue that efforts to protect local populations of A. maculatum and R. sylvatica in roadside wetlands should, in part, be aimed at reducing application of road salt near wetlands with high conductivity levels.

Effects of Timber Harvest on Amphibian Populations: Understanding Mechanisms from Forest Experiments

Harvesting timber is a common form of land use that has the potential to cause declines in amphibian populations. It is essential to understand the behavior and fate of individuals and the resulting consequences for vital rates (birth, death, immigration, emigration) under different forest management conditions. We report on experimental studies conducted in three regions of the United States to identify mechanisms of responses by pond-breeding amphibians to timber harvest treatments. Our studies demonstrate that life stages related to oviposition and larval performance in the aquatic stage are sometimes affected positively by clearcutting, whereas effects on juvenile and adult terrestrial stages are mostly negative. Partial harvest treatments produced both positive and weaker negative responses than clearcut treatments. Mitigating the detrimental effects of canopy removal, higher surface temperature, and loss of soil-litter moisture in terrestrial habitats surrounding breeding ponds is critical to maintaining viable amphibian populations in managed forested landscapes.

PHYLOGEOGRAPHY AND HISTORY OF GIANT GALAPAGOS TORTOISES

Abstract.— We examined the phylogeography and history of giant Galàpagos tortoise populations based on mito‐chondrial DNA sequence data from 161 individuals from 21 sampling sites representing the 11 currently recognized extant taxa. Molecular clock and geological considerations indicate a founding of the monophyletic Galàpagos lineage around 2–3 million years ago, which would allow for all the diversification to have occurred on extant islands. Founding events generally occurred from geologically older to younger islands with some islands colonized more than once. Six of the 11 named taxa can be associated with monophyletic maternal lineages. One, Geochelone porteri on Santa Cruz Island, consists of two distinct populations connected by the deepest node in the archipelago‐wide phylogeny, whereas tortoises in northwest Santa Cruz are closely related to those on adjacent Pinzón Island. Volcan Wolf, the northernmost volcano of Isabela Island, consists of both a unique set of maternal lineages and recent migrants from other islands, indicating multiple colonizations possibly due to human transport or multiple colonization and partial elimination through competition. These genetic findings are consistent with the mixed morphology of tortoises on this volcano. No clear genetic differentiation between two taxa on the two southernmost volcanoes of Isabela was evident. Extinction of crucial populations by human activities confounds whether domed versus saddleback carapaces of different populations are mono‐ or polyphyletic. Our findings revealed a complex phylogeography and history for this tortoise radiation within an insular environment and have implications for efforts to conserve these endangered biological treasures.

Call-response surveys for monitoring breeding waterbirds

We broadcast vocalizations of pied-billed grebe (Podilymbus podiceps), American bittern (Botaurus lentiginosus), least bittern (Ixobrychus exilis), Virginia rail (Rallus limicola), and sora (Porzana carolina) to derive a standardized method to monitor breeding populations of these secretive waterbirds. Broadcast of tape-recorded calls at 60 wetlands in Maine improved species detectability by 93-1, 320% over passive observation. Detection rates at wetlands where target species were known to occur ranged between 0.56 (least bittern) and 0.86 (pied-billed grebe) per survey visit. Three visits to a wetland were adequate to determine the presence or absence of all species with 90% certainty

EFFECTIVENESS OF CALL-BROADCAST SURVEYS FOR MONITORING MARSH BIRDS

Abstract Many species of marsh birds (e.g. rails and bitterns) are believed to be declining in North America, yet we lack an effective monitoring program to estimate their population trends. Broadcast of prerecorded calls to elicit vocalizations is a commonly used method in surveys of marsh birds, but whether gains in detection and index precision outweigh the drawbacks of call-broadcast is unclear. To evaluate the effectiveness of call-broadcast surveys, we pooled marsh-bird survey data from 8,047 point-count surveys contributed by 11 cooperators and compared numbers of birds detected and variation in numbers detected between call-broadcast and passive surveys. For most rails (particularly Virginia Rails [Rallus limicola]), call-broadcast surveys were effective at increasing the detection probability (e.g. average number of Virginia Rails detected per occupied point was 1.25 for call-broadcast surveys and 0.17 for passive surveys). The proportion of points at which no birds were detected was high for all species (range 74–99%) and was slightly lower on call-broadcast surveys as compared with passive surveys. Coefficient of variation (CV) among replicate surveys was higher for passive surveys, particularly for rails (average CV in number of birds detected per point was 209% for passive surveys and 189% for call-broadcast surveys). On the basis of those results, we recommend a marsh-bird monitoring protocol that includes an initial passive period followed by a period of call-broadcast to provide survey data that incorporate the benefits while avoiding the drawbacks of call-broadcast. We also recommend separating both the passive and the call-broadcast periods into 1-min subsegments that will allow estimates of components of detection probability within the monitoring effort. Efectividad de Censos que Reproducen Vocalizaciones Pregrabadas para Monitorear Aves de Pantano

CHANGES IN FROG AND TOAD POPULATIONS OVER 30 YEARS IN NEW YORK STATE

Lack of historical data against which to measure population trends greatly hampers understanding the status of amphibians. In 2001–2002 we resurveyed a hitherto unexamined baseline of monitoring data established in 1973–1980 at some 300 sites in western, central, and northern New York State, USA, and contrasted population transitions with environmental conditions to identify correlates of population change in American toads (Bufo americanus), northern spring peepers (Pseudacris crucifer), western chorus frogs (Pseudacris triseriata), leopard frogs (Rana pipiens), and wood frogs (Rana sylvatica). At the regional level, loss of habitats along roadsides has been substantial (minimally 7– 12% of sites), yet within remaining wetlands, populations of most anurans have not declined. At the local level, population disappearance was associated with elevated levels of acid deposition (in American toad, spring peeper, western chorus frog, and leopard frog), urban development (American toad and spring peeper), increa...

Demography versus habitat fragmentation as determinants of genetic variation in wild populations

A critical question in conservation biology concerns how loss of natural habitat affects the persistence of plant and animal populations and the distribution of genetic variation within them. In this study a simulation model was used to examine how primary demographic and habitat factors affect secondary population processes and thereby influence population genetic structure. The model revealed that both genetic diversity and divergence were most affected by the proportion of patches in a landscape that remain occupied, which in turn was affected primarily by patch disturbance frequency. Patch carrying capacity also controlled the density of individuals within patches and thereby influenced levels of diversity within populations. Habitat availability influenced dispersal success and thereby secondarily influenced genetic divergence among populations. This study emphasizes that conservation of genetic diversity in wild populations should be based on both habitat and population management and can best be achieved by maintaining healthy sized, local populations well-distributed among a network of infrequently disturbed habitats.

Microsatellite analysis of genetic divergence among populations of giant Galápagos tortoises

Giant Galápagos tortoises represent an interesting model for the study of patterns of genetic divergence and adaptive differentiation related to island colonization events. Recent mitochondrial DNA work elucidated the evolutionary history of the species and helped to clarify aspects of nomenclature. We used 10 microsatellite loci to assess levels of genetic divergence among and within island populations. In particular, we described the genetic structure of tortoises on the island of Isabela, where discrimination of different taxa is still subject of debate. Individual island populations were all genetically distinct. The island of Santa Cruz harboured two distinct populations. On Isabela, populations of Volcan Wolf, Darwin and Alcedo were significantly different from each other. On the other hand, Volcan Wolf showed allelic similarity with the island of Santiago. On Southern Isabela, lower genetic divergence was found between Northeast Sierra Negra and Volcan Alcedo, while patterns of gene flow were recorded among tortoises of Cerro Azul and Southeast Sierra Negra. These tortoises have endured heavy exploitation during the last three centuries and recently attracted much concern due to the current number of stochastic and deterministic threats to extant populations. Our study complements previous investigation based on mtDNA diversity and provides further information that may help devising tortoise management plans.