No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
HierarcHical analysis of ampHibian Diversity in primary anD seconDary rain forests of central vietnam
Abstract
We assessed species composition, diversity, and distribution patterns of rain forest amphibian assemblages in central Vietnam using a hierarchical analysis of diversity across study areas and different habitat types. We also plotted rarefaction curves to compare unequal assemblages of amphibians and compared the results with our field observations. We recorded 13,529 individuals of 100 species from Anura and Gymnophiona, comprising eight families and 33 genera. There was an overall similarity in species composition of 0.86 between two areas, A Luoi and Nam Dong, Thua Thien Hue Province, central Vietnam; however, the overall similarity in species composition between primary and secondary forests was only 0.03. Only 29 species (29%) of total recorded amphibians were found in both forest types. The relative abundance and species richness were significantly higher in primary forests than in secondary forests. In both areas, rarefaction curves revealed that the expected number of amphibian species in primary forests was significantly richer than that in secondary forests, suggesting that assemblages of amphibians in interior forest habitat may be more vulnerable to alterations caused by disturbances, such as logging. The lognormal model to predict the expected total number of species theoretically available for observation in the entire community (including the rare species not yet collected) indicated that the expected total number of species is approximately 105, with the number of unseen species predicted to fall below the veil line estimated at about 4.48.
Ếch bám đá Amolops ricketti (group) là một loài có giá trị về dinh dưỡng, dược liệu. Tuy nhiên, thông tin về dị hình kích thước giới tính (SSD), sử dụng vi môi trường sống, phương thức hoạt động của loài này ít được biết đến. Chúng tôi đã quan sát các tập tính của loài này trong quá trình thực địa tại Vườn Quốc gia Bạch Mã kết hợp với việc phân tích các đặc điểm hình thái trong phòng thí nghiệm. Trên cơ sở 97 mẫu Ếch bám đá trưởng thành (44 con đực và 53 con cái), những đánh giá và so sánh các số đo hình thái, tính toán chỉ số SSD đã được thực hiện. Các kết quả cho thấy rằng chiều dài thân (SVL) trung bình của con cái trưởng thành lớn hơn con đực trưởng thành với chỉ số SSD = 0,23. Ếch bám đá sống ở nước suối chảy xiết, với vi môi trường sống chủ yếu trên các vách đá độ dốc cao chiếm ưu thế (52,58%), tiếp đến là các vách đá có độ dốc thấp (34,02%). Thời gian sử dụng cho các hoạt động nằm chờ chiếm tỷ lệ cao nhất (77,78%), phương thức hoạt động của loài này phù hợp với mô hình ngồi và đợi (sit-and-wait) hơn mô hình tìm kiếm rộng (wide forager). Một số chỉ tiêu lí hoá môi trường tại khu vực sống của loài cũng được khảo sát trong nghiên cứu này.
Habitat change is the primary cause of biodiversity loss worldwide. Large tracks of primary forest can be (1) degraded by human-induced disturbance to the point of total conversion into alternative non-forest land-use types, or (2) reduced into small forest fragments isolated within an anthropogenic matrix. Such disturbed habitats are further prone to be colonized by disturbance-adapted species, which can offset species extinctions therein. Here we investigate amphibian and lizard responses to different degrees of habitat degradation and fragmentation, in terms of both species richness and composition, across the neotropics. We then partitioned the β-diversity into its species replacement and richness-difference components to further examine changes in amphibian and lizard species composition. Based on a comprehensive compilation of 67 studies, we observed increasing rates of amphibian and lizard species loss, particularly along the habitat degradation gradient. There were considerable shifts in species composition for both taxa at human-disturbed sites, which were compounded by species replacements. Novel environmental features of disturbed sites clearly benefited synanthropic generalists at the expense of strict forest habitat specialists. As such, we recommend avoiding the use of species richness as a single metric in evaluating the effects of habitat disturbance on biodiversity. Our findings further highlight the critical importance of retaining large expanses of relatively undisturbed forest within anthropogenic landscapes to prevent pervasive species losses and changes in community structure.
Species richness was positively correlated with leaf-litter depth, and negatively correlated with elevation. Herpetofaunal density also tended to increase with litter depth and decline with elevation. A strong positive correlation existed between species richness and herpetofauna density. Evenness was highly variable and independent of both leaf-litter depth and elevation. Local herpetofaunas typically consist of a few very common species along with a large number of comparatively rare species. -from Authors
In adjacent areas of broadleaf evergreen forest, deciduous dipterocarp forest, and agricultural land in northeastern Thailand, >4,000 individuals of 105 species of reptiles and amphibians were systematically collected. The position of capture of each individual was recorded in terms of a complex microhabitat code. The 3 environments differ substantially in pattern of human disturbance, in vegetation structure, and in range and predictability of temperature and total evaporation, the evergreen forest having the most buffered climate near the ground. Of the 3 environments studied, the evergreen forest has the most diverse and distinct herpetofauna, and the largest percentage of autochthonous species. The evergreen forest community has more southern or tropical affinities, while the deciduous forest community has more northern affinities. Analysis of the use of microhabitat categories by coexisting species reveals significant differences, even among the most similar sets of species. Differences in species richness among the three communities are not explained by differences in microhabitat diversity, mean niche breadth, or mean niche overlap. However, an ith nearest neighbor analysis of the dispersion of niche centers in resource space reveals closer packing and larger and more distinct guilds in the evergreen forest: the environment richest in species and the most predictable in climate. Both a graphical treatment and an analysis of sets of species grouped a priori according to their general natural history confirm the existence of larger and significantly tighter guilds in the evergreen forest. It is suggested that unpredictable environments tend to prevent the formation of distinct guilds, while the greater species richness of more predictable environments may be a function of guild formation.
Conhecer a eficácia de diferentes técnicas de amostragem é importante para o avanço nas pesquisas sobre abundância e distribuição de anfíbios e répteis em florestas tropicais. Entretanto, os estudos existentes apresentam um viés ao enfocar apenas certas técnicas, grupos de espécies ou regiões geográficas. Buscando suplantar esse problema, apresentamos a primeira comparação padronizada entre padrões de riqueza de espécies, abundância relativa e estrutura da comunidade, obtidas tanto a partir de técnicas de amostragem passiva quanto ativa, em uma paisagem de floresta tropical. Além disso, comparamos a eficácia desses métodos em floresta primária, secundária e áreas de plantio de Eucalyptus. Embora os diferentes métodos tenham capturado diferentes números de indivíduos e de espécies, a maioria apresentou resultados complementares, tanto para lagartos quanto para anfíbios de serrapilheira. A utilização de um número limitado de técnicas pode levar a resultados fortemente tendenciosos sobre as mudanças que ocorrem na estrutura da comunidade de lagartos e anfíbios em resposta a uma mudança de hábitat em larga escala. Contrário a outros estudos, recomendamos a utilização de armadilhas de interceptação e queda em qualquer caso, inclusive em programas de levantamentos rápidos (RAPs), pois são indispensáveis na amostragem de muitas espécies crípticas, além de apresentar custo-benefício particularmente bom em pesquisas de larga escala. Devido à complementaridade entre os métodos e à influência da técnica sobre a resposta dos táxons às mudanças de hábitat, o presente estudo recomenda a utilização, sempre que possível, de várias técnicas de amostragem. A utilização concomitante de vários métodos, nos estudos de campo, ajudará na obtenção de amostragens mais representativas e, dessa forma, contribuirá para o entendimento sobre a distribuição das espécies e os impactos antrópicos sobre a herpetofauna em florestas tropicais.
Madagascar has one of the world's highest rates of human population increase, which is coupled with an increase of resource exploitation, particularly food and firewood. Forests are cleared and converted to rice fields or plantations (mainly Eucalyptus or pine). How does deforestation affect the amphibian diversity of the original biotope, the rain forest? To answer this question, the amphibian fauna of intact rain forests was compared with that of secondary forests, Eucalyptus plantations and rice fields. The main consequence of rain forest disturbance was loss of amphibian species. Compared with an intact forest, species richness in secondary forests, Eucalyptus plantations and rice fields were 54%, 46% and 12%, respectively. Species number and individual density increased with increasing structural complexity of the habitat and the presence of water bodies. The reproductive strategy of the species could be decisive for the presence or absence of single species in different habitats. With increasing degradation the percentage of species spawning in water increased. Correspondingly, Hyperoliidae and Raninae were characteristic of degraded habitats, whereas Microhylidae and Mantellinae were representative of natural habitats.
The potential effect of forest type on the structuring of animal communities in western Amazonia remains poorly understood. In this study, we tested the hypothesis that amphibian species richness, composition and abundance differ across forest types in the lowland rain forest of south-eastern Peru. By using 320 individual transects, we compared the amphibian assemblages across four major forest types (floodplain, terra firme, bamboo and palm swamp) at each of four sites separated by 3.5-105 km. We identified 1967 individuals of 65 species in 11 families and found that a large proportion of the amphibian diversity in this region is attributed to habitat-related beta diversity. Overall, we found that forest type is more important than site in predicting both species composition and abundance. We also found that, when analyses are conducted separately for each forest type and include species abundance data, similarity between assemblages decreases with increasing geographic distance. In contrast to studies that considered species presence/absence but ignored species abundances, our results highlight the importance of including abundance data in the assessment of animal diversity patterns in western Amazonia. We conclude that evaluating community structure across forest types can improve our understanding of diversity patterns in this region.
An on-going controversy in community ecology involves the debate about the many factors that affect the assembly and composition of a given species assemblage. Theory suggests that community composition is influenced by environmental gradients or biotic processes. This study examines patterns of community composition in two tropical tree frog assemblages of primary and exploited lowland rain-forest sites in the Guiana Shield area of central Guyana, South America and the Upper Guinean rain-forest block of south-western Côte d'Ivoire, West Africa. We tested community composition and species abundance data of two adult tree frog communities collected on 21 standardized transects during a period of 5 y for evidence of spatial correlation in community composition. We applied simple and partial Mantel tests to separate the effects of environmental variables, spatial distance and spatial autocorrelation on community composition. Whenever environmental effects were accounted for, we found significant positive spatial correlation of community composition. All assemblages appeared to be spatially structured, i.e. sites in close proximity had similar species assemblages. However, spatially structured environmental variation (autocorrelation) did not account for the spatial structure of species incidence. Environmental factors did not prove to be significant predictors of species incidence in any of the assemblages analysed, even if we controlled for spatial effects. Observed correlation patterns of species composition were consistent within respective realms and disturbance regimes. Moreover, general correlation patterns were consistent between geographic regions. These results are in contrast to previously published results from a study on leaf-litter anurans and indicate that group-specific differences must not be neglected when analysing patterns of species composition in anurans as they may drastically alter the outcome of the analysis.
Nondetection of a species at a site does not imply that the species is absent unless the probability of detection is 1. We propose a model and likelihood-based method for estimating site occupancy rates when detection probabilities are 1. The model provides a flexible framework enabling covariate information to be included and allowing for missing observations. Via computer simulation, we found that the model provides good estimates of the occupancy rates, generally unbiased for moderate detection probabilities (0.3). We estimated site occupancy rates for two anuran species at 32 wetland sites in Maryland, USA, from data collected during 2000 as part of an amphibian monitoring program, Frog-watch USA. Site occupancy rates were estimated as 0.49 for American toads (Bufo amer-icanus), a 44% increase over the proportion of sites at which they were actually observed, and as 0.85 for spring peepers (Pseudacris crucifer), slightly above the observed proportion of 0.83.
We report on the use of a hybrid marking technique (VIE-C) combining Visible Implant Elastomer (VIE) marks with toe-clipping (C) to mark individuals of several species of treefrogs (Hylidae). Our marking strategy entailed injecting elastomer into the plantar surface of the digits and clipping only one toe. This method allows large numbers of frogs to be individually marked, reduces the potential for negative effects due to clipping multiple toes, and minimizes the frequency of elastomer migration from the injection site, a common problem with VIE marks on the body or limbs. We found retention rate of VIE marks in the digits to be similar to that of toe-clips, indicating that VIE provides a satisfactory alternative to multiple toe-clips. In addition, cost of materials, frog handling time, and ill effects were minimal. This VIE-C marking scheme is highly recommended when considering techniques for marking anurans, as it reduces potential negative effects of clipping multiple toes, and provides a large number of inexpensive and long-lasting individual marks that can be easily applied and quickly read in the field by trained observers.
The global decline in amphibian diversity has become an international en-vironmental problem with a multitude of possible causes. There is evidence that pesticides may play a role, yet few pesticides have been tested on amphibians. For example, Roundup is a globally common herbicide that is conventionally thought to be nonlethal to amphibians. However, Roundup has been tested on few amphibian species, with existing tests conducted mostly under laboratory conditions and on larval amphibians. Recent laboratory studies have indicated that Roundup may be highly lethal to North American tadpoles, but we need to determine whether this effect occurs under more natural conditions and in post-meta-morphic amphibians. I assembled communities of three species of North American tadpoles in outdoor pond mesocosms that contained different types of soil (which can absorb the pesticide) and applied Roundup as a direct overspray. After three weeks, Roundup killed 96–100% of larval amphibians (regardless of soil presence). I then exposed three species of juvenile (post-metamorphic) anurans to a direct overspray of Roundup in laboratory containers. After one day, Roundup killed 68–86% of juvenile amphibians. These results suggest that Roundup, a compound designed to kill plants, can cause extremely high rates of mortality to amphibians that could lead to population declines.
Aim To test how far can macroecological hypotheses relating diversity to environmental factors be extrapolated to functional and phylogenetic diversities, i.e. to the extent to which functional traits and evolutionary backgrounds vary among species in a community or region. We use a spatial partitioning of diversity where regional or γ-diversity is calculated by aggregating information on local communities, local or α-diversity corresponds to diversity in one locality, and turnover or β-diversity corresponds to the average turnover between localities and the region.
Timber harvesting is currently the most common commercial utilisation activity in tropical forests. Assessing the effects of logging on different aspects of biodiversity and general ecosystem properties is hence of prime importance if the few remaining areas of intact tropical forest are to be protected effectively and efficiently.
As we will point out in this chapter, tropical amphibian communities are an appropriate model system for studies on the impacts of human-induced environmental changes on the dynamics of complex biological systems. Here, we elaborate on patterns of diversity changes in tropical forest amphibian communities facing habitat alterations associated with selective logging in two globally important eco-regions (Côte d’Ivoire, Upper Guinea, West Africa and Guyana, the Guiana Shield, northern South America), and discuss findings from other previously conducted studies with similar focus.
A key statement that we stress on in this chapter is the fact that common measures of diversity, such as species richness and α-diversity only inadequately reflect processes of diversity change following anthropogenic disturbance. They also fail to describe actual impacts on the dynamics of complex biological systems. We argue that commonly used measures produce an incoherent and insufficient picture of diversity patterns and the underlying processes that shape these patterns. Thus, an understanding of higher levels of diversity, such as β-diversity and functional diversity (and hence compositional patterns) appears to be the key to effectively mitigating the impacts of human-induced disturbance on amphibian communities.
We show that the predictability of amphibian community composition depends on the respective level of anthropogenic disturbance imposed on a particular habitat. Hence, human activities that lead to changes in the structure of a forest, such as logging, not only alter simple system descriptors, such as the number of species in a given community, but rather alter the dynamics of the entire system. In this context, functional diversity is shown to be an important aspect underlying the actual mechanism that leads to the observed change of predictability patterns. Functional differences between species, rather than number of species per se appear to be the decisive factor in sustaining desirable ecosystem states and thus in maintaining important ecosystem services.
Because biological diversity appears to play a substantial role in ecosystem resilience required to safeguard essential ecosystem functions in the face of environmental change, we call for a critical revision of common diversity assessments approaches. We advocate the reconsideration of the uncritical use of widespread measures and descriptors of biodiversity on grounds of inconsistent patterns found throughout numerous studies, including those presented herein.
The complex nature of natural communities and the multiple aspects of biodiversity at different levels, make it necessary to incorporate processes acting on different organizational and spatial scales. When investigating the impacts of human-induced environmental changes on diverse vertebrate communities in the tropics, we should hence address compositional changes, as well as β-, and functional aspects of biodiversity. Special attention should also be drawn to the particular disturbance history of a given site and large scale cross-regional comparisons should be given priority. The consideration of these approaches in future studies would likely provide deeper insight in ecosystem processes at large scales and improve the effectiveness of current ecosystem management strategies.
A popular way to suggest a regional influence on local species diversity has been to plot local versus regional diversity. The form of the curves has been interpreted as evidence for or against "community saturation" due to species interactions. This interpretation, however is unwarranted. uisng the concepts of a, b & g diversity, I show that the local-regional richness curves are determined by the way total diversity is partitioned between its a & b components, which itself is a matter of scale. Changing the scale of the local community amounts to changing the scale at which the heterogeneity of the interactions between organisms and their environment manifests itself, and hence the balance between a & b diversity. Community saturation may occur because of physical limitations, but there is no theoretical grounds for the belief that species interactions set an absolute limit to diversity at any scale. A distinction between different meanings of the concept of "saturation" is proposed to clarify this issue. I agrue that the challenge now is to understand the relationship between alpha & beta diversity at multiple scales, and the processes that determine it.
The first global assessment of amphibians provides new context for the well-publicized phenomenon of amphibian declines. Amphibians
are more threatened and are declining more rapidly than either birds or mammals. Although many declines are due to habitat
loss and overutilization, other, unidentified processes threaten 48% of rapidly declining species and are driving species
most quickly to extinction. Declines are nonrandom in terms of species' ecological preferences, geographic ranges, and taxonomic
associations and are most prevalent among Neotropical montane, stream-associated species. The lack of conservation remedies
for these poorly understood declines means that hundreds of amphibian species now face extinction.
As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with 'very high confidence' (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.
We investigated the composition, diversity, and patterns of spatial use of an anuran community following a wetland restoration project in a managed tropical monsoon forest in southern Taiwan. Anurans comprising eight species in seven genera and four families reached a mean density of 0.025+/-0.004 anurans m(-2) within a year. The three most important species in terms of frequency of occurrence and relative abundance all had an early appearance; only the most abundant Fejervarya limnocharis (62.2% of total accounts), however, remained present throughout the entire year. The distribution of anurans observed among habitat zones was non-random, with most records occurring in densely planted (42.8%) and running-water (23.9%) zones, and the fewest in a buffer zone adjacent to a paved road. Mean numbers of anurans were correlated with the mean percent vegetation cover among individually divided small pools. Microhyla ornate, M. heymonsi, Polypedates megacephalus, and F. limnocharis appeared to be more heterogeneous in their use of space than Buergeria japonicus. Species differed in their most frequently used habitat zones within the wetland site, with the pairs F. limnocharis and P. megacephalus, and M. ornate and Bufo melanostictus, exhibiting similar respective distributions among zones. Our study demonstrates the value of even a small, isolated wetland in contributing to and maintaining regional amphibian diversity. Patterns of spatial relationships of this anuran community have important implications for the conservation of local populations across species.
Amphibians stand at the forefront of a global biodiversity crisis. More than one-third of amphibian species are globally threatened, and over 120 species have likely suffered global extinction since 1980. Most alarmingly, many rapid declines and extinctions are occurring in pristine sites lacking obvious adverse effects of human activities. The causes of these “enigmatic” declines remain highly contested. Still, lack of long-term data on amphibian populations severely limits our understanding of the distribution of amphibian declines, and therefore the ultimate causes of these declines. Here, we identify a systematic community-wide decline in populations of terrestrial amphibians at La Selva Biological Station, a protected old-growth lowland rainforest in lower Central America. We use data collected over 35 years to show that population density of all species of terrestrial amphibians has declined by ≈75% since 1970, and we show identical trends for all species of common reptiles. The trends we identify are neither consistent with recent emergence of chytridiomycosis nor the climate-linked epidemic hypothesis, two leading putative causes of enigmatic amphibian declines. Instead, our data suggest that declines are due to climate-driven reductions in the quantity of standing leaf litter, a critical microhabitat for amphibians and reptiles in this assemblage. Our results raise further concerns about the global persistence of amphibian populations by identifying widespread declines in species and habitats that are not currently recognized as susceptible to such risks.
• conservation
• long-term studies
• tropical wet forest
Plantation forests and second-growth forests are becoming dominant components of many tropical forest landscapes. Yet there is little information available concerning the consequences of different forestry options for biodiversity conservation in the tropics. We sampled the leaf-litter herpetofauna of primary, secondary, and Eucalyptus plantation forests in the Jari River area of northeastern Brazilian Amazonia. We used four complementary sampling techniques, combined samples from 2 consecutive years, and collected 1739 leaf-litter amphibians (23 species) and 1937 lizards (30 species). We analyzed the data for differences among forest types regarding patterns of alpha and beta diversity, species-abundance distributions, and community structure. Primary rainforest harbored significantly more species, but supported a similar abundance of amphibians and lizards compared with adjacent areas of second-growth forest or plantations. Plantation forests were dominated by wide-ranging habitat generalists. Secondary forest faunas contained a number of species characteristic of primary forest habitat. Amphibian communities in secondary forests and Eucalyptus plantations formed a nested subset of primary forest species, whereas the species composition of the lizard community in plantations was distinct, and was dominated by open-area species. Although plantation forests are relatively impoverished, naturally regenerating forests can help mitigate some negative effects of deforestation for herpetofauna. Nevertheless, secondary forest does not provide a substitute for primary forest, and in the absence of further evidence from older successional stands, we caution against the optimistic claim that natural forest regeneration in abandoned lands will provide refuge for the many species that are currently threatened by deforestation.
An explicit means of calculating the expected number of species [E(S"n)] and the variance of (S"n) in a random sample of n individuals from a collection containing N individuals and S species is presented. An example illustrates a new use of E(S"n): determination of the sample size required for any desired degree of accuracy in collecting species known to occur in a particular area.
The primary emphasis of conservation biology has moved away from attempting to manage single species within a given habitat to the preservation of entire communities within ecoregions, requiring that greater attention be paid to how biodiversity and species composition vary across spatial scales. Using a nested sampling design, we examined spatial variation in the biodiversity of forest Lepidoptera across three hierarchical levels: 20 forest stands, five sites, and three ecoregions. We used blacklight traps to sample the moth communities of each forest stand every week in June and August of 2000. Lepidopteran community composition was most significantly influenced by ecoregional differences, whereas patterns of α and β diversity across scales differed depending on how diversity was measured. Diversity partitioning models demonstrated that turnover in species richness occurred equally across all spatial scales because numerically rare species were continually encountered. In contrast, within-stand effects disproportionately influenced Simpson and Shannon diversity ( relative to outcomes from randomization tests ), suggesting that local factors determined species dominance. Because most Lepidoptera in forests appear to be rare ( >50% ), it will be impossible for conservation biologists to design management plans to account for every species. We suggest that a more meaningful strategy would be to identify species that attain a reasonable abundance within a community ( 5–10% of all the individuals in a sample ) and that are unique to particular spatial levels. This strategy should produce two desirable outcomes: the conservation of species that render ecoregions distinct and the maintenance of functionally dominant species within forests.
We used an experimental approach to investigate the effects of landscape composition on the initial dispersal success of juvenile amphibians. Larval amphibians—spotted salamander (Ambystoma maculatum), small-mouthed salamander (A. texanum), and American toad ( Bufo americanus )—were added to artificial pools in four dispersal arrays on forest edges. Each array consisted of a pool surrounded by a circular drift fence with pitfall traps and two 2.5 × 50 m enclosures (runs) extending into forest and old-field habitat. Juveniles captured at the circular fences were individually marked and released into either field or forest runs. We determined initial distance, initial rate, total distance, and net distance moved by juveniles in the field versus forest from recaptures in the runs. We also conducted 24-hour dehydration trials to compare the rates of evaporative water loss by spotted and small-mouthed salamanders in field and forest. Initial orientation of spotted salamanders and toads was significantly biased toward forest. Orientation of small-mouthed salamanders did not differ significantly from random expectations. The avoidance of open-canopy habitat by juvenile American toads in particular indicates that predictions of dispersal behavior based on adult habitat use may be misleading. Spotted salamanders moved almost four times farther and toads more than three times farther into the forest than into the field, and recapture rates of both species were much lower in the field. We attribute the lower recapture rates and shorter distances moved in the field to higher mortality due to desiccation or an abundance of predators. Juvenile spotted and small-mouthed salamanders experienced greater evaporative water loss in the field. Our data on movement behavior and dehydration rates suggest that old-field habitats offer greater landscape resistance to dispersing juveniles of some species. Thus, forest fragmentation is likely to reduce dispersal rates between local populations of these three species, with potentially negative consequences for population persistence in altered landscapes.
Resumen: Utilizamos un enfoque experimental para investigar los efectos de la composición del paisaje sobre el éxito inicial de dispersión de anfibios juveniles. Colcamos larvas de anfibios (salamandras manchadas [Ambystoma maculatum] y A. texanum y sapo americano [Bufo americanus] ) en estanques artificiales en cuatro secuencias de dispersión en bordes de bosque. Cada secuencia consistió de un estanque rodeado por un cerco circular con trampas de fosa y dos encierros (corridas) de 2.5 × 50 m que se extendían hacia el hábitat de bosque y de campo viejo. Los juveniles capturados en los cercos circulares fueron marcados individualmente y liberados en las corridas de bosque o de campo. A partir de recapturas en las corridas, determinamos la distancia inicial, la tasa inicial, las distancia total y la distancia neta recorrida por juveniles en el campo versus el bosque. También realizamos pruebas de deshidratación de 24 horas para comparar las tasas de pérdida de agua por evaporación en salamandras en el campo y el bosque. La orientación inicial de Ambystoma maculatum y Bufo americanus estuvo significativamente sesgada hacia el bosque. La orientación inicial de A. texanum no fue significativamente diferente de las expectativas aleatorias. La evasión del hábitat abierto en particular por juveniles de sapo americano indica que las predicciones del comportamiento de dispersión basadas en el uso del hábitat por adultos pueden llevar a conclusiones erróneas. Las salamandras manchadas se movieron cuatro veces mas lejos y los sapos más de tres veces más lejos dentro del bosque que dentro del campo, y las tasas de recaptura de ambas especies fueron mucho menores en el campo. Atribuimos las bajas tasas de recaptura y las distancias menores a la mayor mortalidad debido a la desecación o a la abundancia de depredadores. Los juveniles de las dos especies de salamandras experimentaron mayor pérdida de agua por evaporación en los campos. Nuestros datos del comportamiento de movimiento y las tasas de deshidratación sugieren que los hábitats de campo viejo ofrecen mayor resistencia de paisaje para los juveniles dispersantes de algunas especies. Por tanto, es probable que la fragmentación de bosques reduce las tasas de dispersión entre poblaciones locales de estas tres especies, con consecuencias potencialmente negativas para la persistencia de la población en paisajes alterados.
Recent warming has caused changes in species distribution and abundance, but the extent of the effects is unclear. Here we investigate whether such changes in highland forests at Monteverde, Costa Rica, are related to the increase in air temperatures that followed a step-like warming of tropical oceans in 1976 (refs4, 5). Twenty of 50 species of anurans (frogs and toads) in a 30-km2 study area, including the locally endemic golden toad (Bufo periglenes), disappeared following synchronous population crashes in 1987 (refs 6-8). Our results indicate that these crashes probably belong to a constellation of demographic changes that have altered communities of birds, reptiles and amphibians in the area and are linked to recent warming. The changes are all associated with patterns of dry-season mist frequency, which is negatively correlated with sea surface temperatures in the equatorial Pacific and has declined dramatically since the mid-1970s. The biological and climatic patterns suggest that atmospheric warming has raised the average altitude at the base of the orographic cloud bank, as predicted by the lifting-cloud-base hypothesis,.
Large-scale amphibian conservation often relies on remotely sensed data to describe spatial patterns in occupancy. Commonly used data include ownership, forest type, soil class, and proximity of wetlands. We evaluated the influence of these variables on terrestrial amphibian occupancy in southern Michigan. We trapped amphibians using drift-fence arrays in 82 forest patches and estimated detection probabilities for all captured species. Ten species were captured, but only three were detected at levels suitable for occupancy modeling. We concluded that drift-fence arrays alone were not sufficient for adequately detecting the majority of terrestrial amphibians. The best detection models for American Toad (Anaxyrus americanus), Wood Frog (Lithobates sylvaticus), and Spring Peeper (Pseudacris crucifer) consistently included a positive relationship with temperature and precipitation. Detection-adjusted occupancy models for the three anurans indicated relatively high occupancy (>0.43). Ownership, forest type, and soil class did not occur in higher ranking occupancy models. Rather, the higher ranking models often included the distance to National Wetlands Inventory (NWI) wetland and sample year factors. However, these effects were highly variable and of no use in consistently predicting terrestrial amphibian occupancy. Our results substantiate the importance of incorporating detection probabilities into studies of amphibian habitat relationships and suggest that coarse descriptors of environmental conditions may not adequately portray factors important to terrestrial amphibian occupancy.
Disentangling local and historical factors that determine species diversity patterns at multiple spatial scales is fundamental to elucidating processes that govern ecological communities. Here we investigated how environmental correlates may influence diversity at local and regional scales. Primarily utilizing published species lists, amphibian and reptile alpha and beta diversity were assessed at 17 well-surveyed sites distributed among ecoregions throughout Costa Rica. The degree to which regional species diversity patterns were related to environmental variables and geographic distance was determined using Canonical Correspondence Analysis and Mantel tests. Amphibian alpha diversity was highest in lowland Pacific sites (mean = 43.3 species) and lowest at the high elevation site (9 species). Reptile alpha diversity values were high for both lowland Atlantic (mean = 69.5 species) and lowland Pacific (mean = 67 species) sites and lowest for the high elevation site (8 species). We found high species turnover between local sites and ecoregions, demonstrating the importance of beta diversity in the determination of regional diversity. For both amphibians and reptiles, beta diversity was highest between the high-elevation site and all others, and lowest among lowland sites within the same ecoregion. The effect of geographic distance on beta diversity was minor. Ecologically significant climatic variables related to rain, temperature, sunshine and insolation were found to be important determinants of local and regional diversity for both amphibians and reptiles in Costa Rica.
Effective monitoring programs are designed to track changes in the distribution, occurrence, and abundance of species. We developed an extension of Royle and Kéry's (2007) single species model to estimate simultaneously temporal changes in probabilities of detection, occupancy, colonization, extinction, and species turnover using data on calling anuran amphibians, collected from 2002 to 2006 in the Lower Mississippi Alluvial Valley of Louisiana, USA. During our 5-year study, estimates of occurrence probabilities declined for all 12 species detected. These declines occurred primarily in conjunction with variation in estimates of local extinction probabilities (cajun chorus frog [Pseudacris fouquettei], spring peeper [P. crucifer], northern cricket frog [Acris crepitans], Cope's gray treefrog [Hyla chrysoscelis], green treefrog [H. cinerea], squirrel treefrog [H. squirella], southern leopard frog [Lithobates sphenocephalus], bronze frog [L. clamitans], American bullfrog [L. catesbeianus], and Fowler's toad [Anaxyrus fowleri]). For 2 species (eastern narrow-mouthed toad [Gastrophryne carolinensis] and Gulf Coast toad [Incilius nebulifer]), declines in occupancy appeared to be a consequence of both increased local extinction and decreased colonization events. The eastern narrow-mouthed toad experienced a 2.5-fold increase in estimates of occupancy in 2004, possibly because of the high amount of rainfall received during that year, along with a decrease in extinction and increase in colonization of new sites between 2003 and 2004. Our model can be incorporated into monitoring programs to estimate simultaneously the occupancy dynamics for multiple species that show similar responses to ecological conditions. It will likely be an important asset for those monitoring programs that employ the same methods to sample assemblages of ecologically similar species, including those that are rare. By combining information from multiple species to decrease the variance on estimates of individual species, our results are advantageous compared to single-species models. This feature enables managers and researchers to use an entire community, rather than just one species, as an ecological indicator in monitoring programs. © 2011 The Wildlife Society.
Over the last two decades, numerous studies have shown that alien predators contributed to amphibian population declines. Both experimental studies and correlative field surveys implicated alien species of fish, bullfrogs and crayfish as major contributors to amphibian population decline, and in some instances local extinction. Additional studies have demonstrated that alien predators also caused long-term changes in aquatic communities. Recent studies have examined the feasibility of removing alien predators, and provide some evidence that amphibian populations can recover. Applying information gained from past studies to the recovery of amphibian populations will be the challenge of future studies. International, national and local policies that regulate alien predators should be based largely on the body of scientific evidence already in the literature. Scientists need to be more involved with policy-makers to most effectively change laws that regulate alien predators.
Ten species of small vertebrates that occurred together in leaf litter of the Amazon tropical rainforest were studied during the dry season in Rondônia, western Brazil. This vertebrate assemblage consisted of two diurnal lizards, two diurnal frogs, one nocturnal frog, and five frog species that are active by day and night. All species feed on small invertebrates, primarily insects and arachnids. There are significant differences in prey types and sizes eaten, and overlap values among species are relatively low. Niche breadths vary from unity (extremely low) to high (> 9.0). A pseudocommunity analysis using two different algorithms indicated that structure exists in the prey resource matrix of the vertebrate assemblage. The zero structure of the community matrix contributes to the observed structure, i.e. prey items not taken by certain species are important in maintaining structure. Several well-defined feeding guilds are apparent, and the feeding guilds do not appear to follow taxonomic lines.
In community ecology, contrasting theories suggest that the distribution and abundance of species, and thus the composition of assemblages, are influenced by i) environmental gradients, or ii) contagious biotic processes such as predation, competition, dispersal and disease. In the former case, sites with similar environments would tend to support similar assemblages, while in the latter, geographically proximate sites would tend to support more similar assemblages than widely separated sites. I investigated the relative influence of environmental variables and spatial position on the composition of frog assemblages at forest streams in sub-tropical eastern Australia using redundancy analysis (RDA) and partial RDA. Data on the maximum abundance of the frog species at 65 survey sites were transformed such that RDA would yield the Hellinger distance between sites. The following analysis identified 11 environmental variables that explained 45% of the variation in the abundance of species at the survey sites (the species matrix), as a proportion of total variance. The geographic co-ordinates of the survey sites accounted for 12%, while the environmental and spatial variables combined accounted for 47% of the variation in the species matrix. Partial redundancy analysis indicated that of the explained variation, 74% was purely environmental, 5% was purely spatial and 21% was spatial environmental variation. This study is the first to quantify the relative influence of environmental and spatial variables on the composition of amphibian assemblages. It provides support for both the environmental control model and the biotic control model of species’ distributions and assemblage composition, although environmental variables appear to have the greater effect at this scale of analysis.
We present data on sample richness, relative abundance, and community structure of a leaf litter amphibian assemblage from globally important miombo-mopane woodlands characteristic of western Tanzania. We describe patterns of diversity across major habitat types and between different seasons from an annual pitfall-trapping campaign. We recorded 28 species of amphibians, which is significantly higher than existing richness estimates for other miombo woodland sites elsewhere in sub-Saharan Africa. We found that cultivation of native habitat reduces frog diversity, a conclusion that has important implications in light of the rapid conversion of miombo woodland for agriculture and fuel-wood across much of southern and central Africa. Many species showed strongly ansynchronized patterns of seasonality in relative abundance, which has significant implications for the establishment of successful monitoring programs and biodiversity surveys. These conclusions emphasize the importance of stratified long-term sampling in biodiversity studies and demonstrate that superficial levels of sampling effort can lead to erroneous conclusions regarding patterns of diversity in amphibian communities. The relatively poor focus on herpetofaunal research in African miombo-mopane woodland is out of proportion to its ecological and conservation significance.
Relationships between diurnal, terrestrial birds, vegetation and environmental attributes were investigated in the open Eucalyptus forests of south east Australia. Of the 83 bird species recorded, the probability of occurrence of the Yellow-faced Honeyeater, Superb Fairy-wren, Golden Whistler, Fan-tailed Cuckoo and Shining Bronze-Cuckoo was modelled. The Yellow-faced Honeyeater was the only taxon modelled whose distribution could be best explained using climatic variables. The other four species were related to habitat features at the site level. The models developed for these species were specific to each data set used and are unlikely to be appropriate for other data collected at other times of the year. Statistical modelling was used to investigate the response of bird assemblages to environmental and biological regimes. The models reflect differences in the bird species composition of sites in relation to elevation and soil moisture/nutrient gradients across the region. Birds favouring higher elevations were separated from birds favouring mid and lower elevations. Birds favouring wetter environments were separated from those using drier habitats although these species were also present in the wetter environments. Differences in the distribution of birds related to elevation were explained by the environmental attributes minimum temperature of the coldest month and mean precipitation of the driest quarter which also affect vegetation formations and associations across the study region. Vegetation floristics and topographic position, which can reflect the moisture and nutrient status of sites, were important in characterising the specific habitat requirements of a number of birds. Physical and biological regimes were significantly related to bird species richness. Species richness was found to be greatest in moist forests found at mid and low elevations throughout the year. A stratified field survey was successful in recording the majority of forest birds that can occur in the eucalypt forests of south east Australia but sufficient data for reliably modelling the distribution and habitat quality of birds were obtained for only about 10% of the birds recorded. Even when data from two census periods were aggregated, data were sufficient for only 27% of the total number of birds recorded to develop a habitat model. Suggested modifications to the survey design based on the data and analyses used in this study, are discussed in terms of the intended purpose of the field survey.
Many indices have been proposed for measuring species evenness in ecological communities, but there is no consensus on which are best. We assemble criteria for an appropriate index for the evenness of a biological sample. The most important criterion is that evenness should be independent of species richness. Twelve previously proposed indices and variants are considered, and two apparently new indices. Four indices are recommended as joint best buys: A) If symmetry between minor and abundant species is not important, or if it is required that the index be less affected by minor species: 1) If it is essential that the index be able to reach a minimum of zero with any particular number of species, or if the shape of the index response to an evenness gradient is important: E1/D (based on a common form of Simpson's index). 2) If good mid-range behaviour is desired: E′ (proposed by Camargo). B) If equal sensitivity to minor and abundant species is required: 1) If the shape of the index response to an evenness gradient is not important, the clear winner is: EQ (a new index). 2) If the shape is important: Evar (another new index). The overall recommendation for general use is Evar.
In this paper a methodology is presented for measuring diversity based on rarefaction of actual samples. By the use of this technique, a within-habitat analysis was made of the bivalve and polychaete components of soft-bottom marine faunas which differed in latitude, depth, temperature, and salinity. The resulting diversity values were highly correlated with the physical stability and past history of these environments. A stability-time hypothesis was invoked to fit these findings, and, with this hypothesis, predictions were made about the diversities present in certain other environments as yet unstudied. The two types of diversity, based on numerical percentage composition and on number of species, were compared and shown to be poorly correlated with each other. Our data indicated that species number is the more valid diversity measurement. The rarefaction methodology was compared with a number of diversity indexes using identical data. Many of these indexes were markedly influenced by sample size. Good...
Species richness, Shannon information, and Simpson diversity are the three most commonly used nonparametric measures of species diversity. The sampling bias and variance of these measures differ greatly. Species richness may be seriously underestimated for even very large samples from a speciose community. The bias in species richness and Shannon information depend on unknown parameters of the species abundance distribution. An unbiased estimator exists only for Simpson diversity. Each of these measures is concave, so that the total diversity in a pooled set of communities exceeds (or equals) the average diversity within communities. The total diversity in a set of communities can therefore be partitioned into positive, additive components within and among communities, corresponding to alpha- and beta-diversity. Partitioning Simpson diversity corresponds to an analysis of variance. The proportion of the total diversity found within communities provides a natural measure of similarity among multiple communities. The expected similarity among multiple random samples from the same community depends on the number of samples and on the underlying measure of diversity.
Part 1. It is shown that in a large collection of Lepidoptera captured in Malaya the frequency of the number of species represented by different numbers of individuals fitted somewhat closely to a hyperbola type of curve, so long as only the rarer species were considered. The data for the commoner species was not so strictly `randomized', but the whole series could be closely fitted by a series of the logarithmic type as described by Fisher in Part 3. Other data for random collections of insects in the field were also shown to fit fairly well to this series. Part 2. Extensive data on the capture of about 1500 Macrolepidoptera of about 240 species in a light-trap at Harpenden is analysed in relation to Fisher's mathematical theory and is shown to fit extremely closely to the calculations. The calculations are applied first to the frequency of occurrence of species represented by different numbers of individuals--and secondly to the number of species in samples of different sizes from the same population. The parameter ` alpha ', which it is suggested should be called the `index of diversity', is shown to have a regular seasonal change in the case of the Macrolepidoptera in the trap. In addition, samples from two traps which overlooked somewhat different vegetation are shown to have ` alpha ' values which are significantly different. It is shown that, provided the samples are not small, ` alpha ' is the increase in the number of species obtained by increasing the size of a sample by e (2.718). A diagram is given (Fig. 8) from which any one of the values, total number of species, total number of individuals and index of diversity (alpha), can be obtained approximately if the other two are known. The standard error of alpha is also indicated on the same diagram. Part 3. A theoretical distribution is developed which appears to be suitable for the frequencies with which different species occur in a random collection, in the common case in which many species are so rare that their chance of inclusion is small. The relationships of the new distribution with the negative binomial and the Poisson series are established. Numerical processes are exhibited for fitting the series to observations containing given numbers of species and individuals, and for estimating the parameter alpha representing the richness in species of the material sampled; secondly, for calculating the standard error of alpha, and thirdly, for testing whether the series exhibits a significant deviation from the limiting form used. Special tables are presented for facilitating these calculations.
The recent literature on species diversity contains many semantic, conceptual, and technical problems. It is suggested that, as a result of these problems, species diversity has become a meaningless concept, that the term be abandoned, and that ecologists take a more critical approach to species-number relations and rely less on information theoretic and other analogies. As multispecific collections of organisms possess numerous statistical properties which conform to the conventional criteria for diversity indices, such collections are not intrinsically arrangeable in linear order along some diversity scale. Several such properties or "species composition parameters" having straightforward biological interpretations are presented as alternatives to the diversity approach. The two most basic of these are simply =the proportion of potential interindividual encounters which is interspecific (as opposed to intraspecific), assuming every individual in the collection can encounter all other individuals, and =the expected number of species in a sample of n individuals selected at random from a collection containing N individuals, S species, and Ni individuals in the ith species.
Consisting of more than six thousand species, amphibians are more diverse than mammals and are found on every continent save Antarctica. Despite the abundance and diversity of these animals, many aspects of the biology of amphibians remain unstudied or misunderstood. The Ecology and Behavior of Amphibians aims to fill this gap in the literature on this remarkable taxon. It is a celebration of the diversity of amphibian life and the ecological and behavioral adaptations that have made it a successful component of terrestrial and aquatic ecosystems. Synthesizing seventy years of research on amphibian biology, Kentwood D. Wells addresses all major areas of inquiry, including phylogeny, classification, and morphology; aspects of physiological ecology such as water and temperature relations, respiration, metabolism, and energetics; movements and orientation; communication and social behavior; reproduction and parental care; ecology and behavior of amphibian larvae and ecological aspects of metamorphosis; ecological impact of predation on amphibian populations and antipredator defenses; and aspects of amphibian community ecology. With an eye towards modern concerns, The Ecology and Behavior of Amphibians concludes with a chapter devoted to amphibian conservation. An unprecedented scholarly contribution to amphibian biology, this book is eagerly anticipated among specialists.
Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.
Ecological Methodology
- C J Krebs
Krebs, C.J. 1999. Ecological Methodology. Addison-Wesley Educational Publishers, Inc., New York, New
York, USA.
- A E Magurran
Magurran, A.E. 2004. Measuring Biological Diversity.
Blackwell Science Ltd., Oxford, UK.
Amphibian diversity in central Vietnam and the distribution pattern and natural history of Granular Spiny Frogs Quasipaa verrucospinosa (Anura: Dicroglossidae)
- B V Ngo
Ngo, B.V. 2015. Amphibian diversity in central Vietnam
and the distribution pattern and natural history of
Granular Spiny Frogs Quasipaa verrucospinosa
(Anura: Dicroglossidae). Ph.D. Dissertation,
National Cheng Kung University, Tainan, Taiwan.
173 p.
Climatic-Hydrology Characters of Thua Thien Hue Province
- Q V Nguyen
- Le
Nguyen, and Q.V. Le. 2004. Climatic-Hydrology
Characters of Thua Thien Hue Province. Thuan Hoa
Publishing House, Hue, Vietnam.