Ambystoma opacum byTim Halliday ISSN 1026-0269 FROGLOG Newsletter of the IUCN /SSC Amphibian Specialist Group (ASG) December 2006, Number 78 amphibian species entering ponds individuals. Computer assisted Impacts of from clearcut versus forest habitats pattern-matching software clearcutting on across years. Of the 149,756 developed specifically for A. amphibians amphibians that were captured opacum by Lex Hiby of after 20 years and included in our analysis, 17 of Conservation Research Ltd. of forest re- 18 species at all ponds in all years (Cambridge, UK) drastically establishment migrated to ponds in significantly reduced the number of photo By: Don R. Church, Henry M. smaller numbers from the clearcut comparisons that needed to be Wilbur and Larissa Bailey habitats than from the forest made by eye. Individuals had habitats associated with each overall high fidelity to their point of The long-term impacts of forestry pond. The one exception was the entry to and exit from a pond within practices on amphibian spring peeper, Hyla crucifer, which and across years. populations remain uncertain. was caught in significantly larger Using recently developed multi- Several studies in eastern North numbers entering from the clearcut state mark-recapture methods America have previously shown habitat at each pond. These (Bailey et al., 2004) and that clearcutting of upland forests results raised the question: Why multimodel inference (Burnham & results in a reduction in the number exactly do fewer amphibians Anderson, 2002) we found that of pond-breeding amphibians that migrate to ponds from clearcut survival probabilities within both migrate to breeding sites. habitats after 20 years of forest breeding and non-breeding However, in general, deciduous reestablishment? The answer to seasons varied among years, forests of eastern North America this question has important populations, and between habitats. are considered relatively resilient implications for how amphibian Annual survival probabilities ranged to logging. A remaining question populations should be managed in from nearly 1 to 0.25 in females and therefore is how amphibian landscapes where forestry is from nearly 1 to 0.48 for males. One populations respond to forest practiced. Competing hypotheses consistency in survival probabilities reestablishment – a process that is among populations was that both include: underway in over 100 million 1) Low counts of animals may female and male salamanders hectares in eastern North America simply reflect historical effects of experienced dramatic mortality alone. initial tree harvesting on during the non-breeding season in a We explored this question in an demographic parameters (i.e., drought year (2001-2002). Interestingly, a previous analysis amphibian assemblage that utilizes populations in clearcuts have not (Church et al., in press) revealed a system of natural sinkhole ponds yet rebounded from mortality, within the George Washington and that the sympatric tiger salamander reduced reproduction, or habitat (Ambystoma tigrinum) did not incur Jefferson National Forest in biased movements that occurred Virginia, USA. Between September high mortality during the non- 20 years ago). breeding season of the drought year 1999 and August 2004, we 2) Survival, annual breeding monitored populations of 18 pond- suggesting that these species differ probability or fecundity remains in their vulnerability to dry conditions breeding amphibian species at 3 reduced in clearcuts. or in what microhabitats they utilize ponds, each approximately 330 3) Animals avoid clearcuts via their in the upland habitats. meters in circumference, using drift movements even after partial Unexpectedly, habitat differences fences, with pitfall traps at 10 forest reestablishment. in survival were overall not meter intervals that completely 4) Combination of above factors. consistent across time or among encircled each pond. Two types We have begun to address populations. Survival probabilities of matrix – a clearcut that was these competing hypotheses with varied such that probabilities were logged in 1989 (hereafter referred a capture-recapture study of sometimes lower and sometimes to as clearcut) and forest that has marbled salamander (Ambystoma higher in clearcut habitats. This not been logged since the early opacum) populations that are finding indicates that survival is 1900’s (hereafter referred to as associated with each pond. We influenced by complex interactions forest), surround each pond in used photos of natural markings among habitat variables, similar proportions. We compared on the dorsal surface of A.opacum populations and climate. the per-pitfall trap counts of each to reconstruct capture histories of 1 Breeding probabilities varied Burnham, K. P., and D. R. The environmental problems in among populations and were Anderson. (2002). Model selection Xochimilco are considered to have found to be Markovian (dependent and multimodel inference: a reduced axolotl populations. In six on whether or not an individual practical information-theoretic years (from 1998 to 2004), axolotl bred in the previous year), ranging approach. 2nd Edition. Springer- density has reduced from 0.006- 2 from 0.22 to 0.52 for animals that Verlag, New York, New York, USA. org/ m to 0.001-org/ m2 had bred the previous year and 488 pp. (Zambrano et al., 2004). This from 0.63 to 0.86 for animals that Church, D.R., L.L. Bailey, H.M. reduction could also be related to had skipped breeding for at least Wilbur, W.L. Kendall &J.E. Hines. its own population dynamics. As one year. Breeding probabilities Iteroparity in the variable egg production is quite high (more also differed between clearcut and environment of the salamander than one thousand eggs are laid forest habitats within each Ambystoma tigrinum. Ecology ( in by healthy females), it suffers from population – they were lower for press). elevated mortality within the first animals entering ponds from For further information please year. These factors have caused clearcuts at two populations by contact Don Church at: some prominent fluctuations in more than 30% but higher at the [email protected] axolotl population dynamics over third population by 29%. the years. These fluctuations Movement probabilities among The Mexican produce high population declines the 3 populations were low Axolotl in some years, but also large (<0.001-0.08). In contrast, (Ambystoma increments in others, causing low movements between forest and mexicanum) extinction probabilities. However, clearcut habitats within populations By Luis Zambrano extinction probabilities can rise up were often high and heavily biased to 100% in the next 50 years if the The Mexican axolotl (Ambystoma towards leaving clearcuts in favour mortality rate of eggs and larva mexicanum) is endemic to the of forest habitat in two populations increases to less than 5% Mexican high plateau and has a but marginally in favour of (Zambrano et al., submitted). recent evolutionary history (less clearcuts in the same population Reductions in egg and larvae than 10 thousand years). For where clearcut animals had higher survival rates are related to the centuries it inhabited the large breeding probabilities. female’s capacity to lay eggs. wetlands that used to occupy most The reasons for these Studies have shown that axolotls of the Mexican Valley. Today, its differences in clearcut effects have particular preferences for distribution has been reduced to among populations remains laying eggs on plants that help to only two remaining water bodies: unclear but may be due to different create more spatial heterogeneity Xochimilco and Chalco. Both geologies underlying the clearcuts (Martinez, 2007). Plants that systems have been under pressure areas. Differences in alluvial provide shadows and holes where from human activities. Chalco was rubble in the landscape are known eggs and larvae can hide and find dry for many years reducing water to influence local hydrology of food are preferred, suggesting that as a result of a reduced water ponds (nearby ponds fill and dry females search for places where table, leaving only a few small on very different schedules) and their eggs will have better survival ponds for the species to survive in. may also create differences in the rates. However, pollution and bank Fortunately, in recent years this quality of habitats for the erosion have decreased the small water system has been subterranean lifestyle of marbled number of suitable locations and growing due to a lake restoration salamanders. Overall, our results structures for laying eggs. This programme to avoid dust storms so far indicate that forest results in the possibility of reduced and axolotls have been seen. clearcutting can have major reproduction rates. Xochimilco has been under impacts on some demographic Another threat which has been pressure as a source of water parameters even after 20 years but increasing in the last few years is since the Aztecs first settled in the that other landscape features may the biomass of introduced carp area in XIII AC. Today, Xochimilco override these effects under and tilapia - 80 times higher than receives water from a water certain conditions. A complete the biomass of native organisms treatment plant instead of natural answer to the question of whether within Xochimilco: carp eat axolotl springs and suffers from domestic these differences in demography eggs, while tilapia prefer to eat sewage. In addition, increased account for the differences in recently