Mark-Oliver Rödel

ANTHROPOGENICALLY INDUCED CHANGES OF PREDICTABILITY IN TROPICAL ANURAN ASSEMBLAGES

Anthropogenic habitat alteration has long been neglected as a factor in the analysis of predictability patterns in biological communities. We tested this factor by investigating anuran leaf litter assemblages in primary and secondary forests of Tai National Park, Ivory Coast, during two years. We measured predictability of assemblage composition by analyzing correlations between the off-diagonal elements of distance matrices based on (1) species distribution, (2) environmental characteristics, and (3) geographic distance. Pairwise correlations between matrices were significant in all cases when considering data pooled across time and habitats. A different pattern emerged when data were split according to season and disturbance level (i.e., primary vs. secondary habitats). Assemblage composition in primary habitats was correlated with geographic proximity of sites exclusively, indicating otherwise stochastic recruitment from a regional species pool at the local community level. In contrast, assemblage comp...

The importance of environmental heterogeneity for species diversity and assemblage structure in Bornean stream frogs

1. Several hypotheses have been proposed to explain the structure of multi-species assemblages. Among these, abiotic environmental factors and biotic processes are often favoured. Several recent studies examining anuran communities identified environmental factors to be only of minor importance in the composition of leaf-litter and canopy assemblages in pristine forests. Instead, spatial effects and spatially structured environments were considered more important. 2. In this study, we investigated whether these findings could also be confirmed for very heterogeneous stream habitats in the primary rainforest of the Ulu Temburong National Park, Brunei Darussalam. We thus investigated anuran assemblage compositions on 50 stream sites with regard to environmental and spatial influences. 3. Cross-product correlations indicated that both factors (spatial and environmental parameters) determined assemblage composition of anurans. Environment itself may be spatially structured, yet this interrelation did not contribute to the explainable variation of frog community compositions within the study area. 4. Detailed analyses of the environmental parameters with nonmetric multidimensional scaling revealed that community structure was mostly affected by three major environmental characters: stream turbidity, river size and the density of understorey vegetation. Based on these habitat characteristics, we assigned species to three distinct habitat guilds. 5. The results underline the importance of riparian habitat heterogeneity in pristine forests in structuring anuran assemblages. We conclude that different anuran assemblages, that is, leaf litter, canopy and stream communities, follow different assemblage rules and thus are not directly comparable.

Effects of Forest Fragmentation and Habitat Degradation on West African Leaf-Litter Frogs

Habitat degradation alters the dynamics and composition of anuran assemblages in tropical forests. The effects of forest fragmentation on the composition of anuran assemblages are so far poorly known. We studied the joint influence of forest fragmentation and degradation on leaf-litter frogs. We specifically asked whether the processes structuring leaf-litter anuran assemblages in fragmented forests are the same as those in continuous forests. We analyzed anuran assemblages with respect to habitat characteristics, including fragmentation and degradation parameters. In comparison with continuous forests, species richness and diversity were lower and assemblage composition was altered in forest fragments. These changes seemed to be mainly caused by habitat degradation rather than forest fragmentation. Availability of aquatic sites for breeding, vegetation structure (including those variables indicating degradation), and leaf-litter cover had the most influence on the presence of single species. The comparatively small impact of fragmentation on anurans might be due to the location of the study area; it still possessed large tracts of continuous forest. These forest blocks may stabilize the regional rainforest climate and thus weaken the effects of fragmentation.

Patterns of community composition in two tropical tree frog assemblages: separating spatial structure and environmental effects in disturbed and undisturbed forests

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 Cote dTvoire, 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.

Putting Toe Clipping into Perspective: A Viable Method for Marking Anurans

Abstract Toe clipping is widely used in studies of amphibian ecology and behavior, but its impact on return rates and survival remains controversial. We evaluated the effect of toe clipping on apparent survival, using four comprehensive mark–recapture data sets of four anuran species covering four different time scales and varying life histories. The effect of toe clipping was evaluated by comparing frogs with different numbers of toes removed. Two species, Eleutherodactylus coqui and Hemisus marmoratus, showed minimal effects of toe clipping on apparent survival with seasonal and annual apparent survival decreasing by 0.1% and 1.5% with toe removal, respectively. In Hyperolius nitidulus, daily apparent survival increased on average by 4.1% with toe removal, an effect than can be attributed to disproportionate emigration of the lowest toe-removal group. Finally, in Phrynobatrachus guineensis, individuals with three toes clipped showed an additional 5.0–19.7% decreased apparent survival between weeks when compared to individuals with only one toe clipped. However, the data set was characterized by an interaction between the number of toes clipped and week of marking, thus confounding interpretation. To minimize any effects of toe clipping, we recommend that not more than four toes should be clipped and at most a single toe removed on each leg. In addition, functionally important toes such as the proximal toes of front feet and fourth toes of hind feet should be spared. Furthermore, toe-removal groups should be equally distributed over time to facilitate the analysis of potential toe-clipping effects.

The use of bioacoustics in anuran taxonomy: theory, terminology, methods and recommendations for best practice

Vocalizations of anuran amphibians have received much attention in studies of behavioral ecology and physiology, but also provide informative characters for identifying and delimiting species. We here review the terminology and variation of frog calls from a perspective of integrative taxonomy, and provide hands-on protocols for recording, analyzing, comparing, interpreting and describing these sounds. Our focus is on advertisement calls, which serve as premating isolation mechanisms and, therefore, convey important taxonomic information. We provide recommendations for terminology of frog vocalizations, with call, note and pulse being the fundamental subunits to be used in descriptions and comparisons. However, due to the complexity and diversity of these signals, an unequivocal application of the terms call and note can be challenging. We therefore provide two coherent concepts that either follow a note-centered approach (defining uninterrupted units of sound as notes, and their entirety as call) or a call-centered approach (defining uninterrupted units as call whenever they are separated by long silent intervals) in terminology. Based on surveys of literature, we show that numerous call traits can be highly variable within and between individuals of one species. Despite idiosyncrasies of species and higher taxa, the duration of calls or notes, pulse rate within notes, and number of pulses per note appear to be more static within individuals and somewhat less affected by temperature. Therefore, these variables might often be preferable as taxonomic characters over call rate or note rate, which are heavily influenced by various factors. Dominant frequency is also comparatively static and only weakly affected by temperature, but depends strongly on body size. As with other taxonomic characters, strong call divergence is typically indicative of species-level differences, whereas call similarities of two populations are no evidence for them being conspecific. Taxonomic conclusions can especially be drawn when the general advertisement call structure of two candidate species is radically different and qualitative call differences are thus observed. On the other hand, quantitative differences in call traits might substantially vary within and among conspecific populations, and require careful evaluation and analysis. We provide guidelines for the taxonomic interpretation of advertisement call differences in sympatric and allopatric situations, and emphasize the need for an integrative use of multiple datasets (bio-acoustics, morphology, genetics), particularly for allopatric scenarios. We show that small-sized frogs often emit calls with frequency components in the ultrasound spectrum, although it is unlikely that these high frequencies are of biological relevance for the majority of them, and we illustrate that detection of upper harmonics depends also on recording distance because higher frequencies are attenuated more strongly. Bioacoustics remains a prime approach in integrative taxonomy of anurans if uncertainty due to possible intraspecific variation and technical artifacts is adequately considered and acknowledged.

Complex patterns of continental speciation: Molecular phylogenetics and biogeography of sub-Saharan puddle frogs (Phrynobatrachus)

Puddle frogs (Anura: Phrynobatrachidae) are one of the most species-rich sub-Saharan amphibian groups, occupying an extraordinarily diverse range of habitats. We construct the first phylogeny of puddle frogs, utilizing mitochondrial (12S rRNA, valine-tRNA, and 16S rRNA) and nuclear (RAG-1) DNA. Phylogenetic analyses are conducted using separate and combined partitions under maximum parsimony, maximum likelihood, and Bayesian criterion. Monophyly of the Phrynobatrachidae is well supported, and three major clades of Phrynobatrachus are identified. We reconstructed a biogeographic history using habitat preference, elevation, and geographic distribution. Habitat niches appear to be conserved between sister species, with the majority of species favoring forest over savanna habitats and the most recent common ancestor of the Phrynobatrachidae reconstructed as a forest species. Analyses of elevational data identify three independent colonizations of highland regions, one in each of the three major clades. Ancestral reconstructions support an East African origination of puddle frogs. Most species are restricted to one of five sub-Saharan regions and are distributed within the Eastern, Central, and Western zones with far fewer species in Southern Africa. These results elucidate the complex patterns of spatial niche partitioning that have contributed to the diversification of this widely distributed, sub-Saharan genus.

A New Phrynobatrachus from the Upper Guinean Rain Forest, West Africa, Including a Description of a New Reproductive Mode for the Genus

Abstract We describe a new species of Phrynobatrachus from the Western part of the Upper Guinean rain forest, West Africa. Phrynobatrachus phyllophilus sp. nov. differs from all other known West African Phrynobatrachus by a combination of morphological and acoustical characters. It is most similar to Phrynobatrachus guineensis from which P. phyllophilus is distinguished by its almost white belly, presence of only one dark bar on femur and tibia, shape of the thumb in reproductive males, advertisement call, reproductive mode, and selection of different forest types. Phrynobatrachus phyllophilus is the first known species of the genus that deposits small clutches of eggs rich in yolk on leaves, in close vicinity to extremely small puddles on the forest floor. Its preferred habitats are swampy areas of primary rain forest. We also describe the tadpole of P. phyllophilus and the advertisement call of P. guineensis.

Predictors of elevational biodiversity gradients change from single taxa to the multi-taxa community level.

The factors determining gradients of biodiversity are a fundamental yet unresolved topic in ecology. While diversity gradients have been analysed for numerous single taxa, progress towards general explanatory models has been hampered by limitations in the phylogenetic coverage of past studies. By parallel sampling of 25 major plant and animal taxa along a 3.7 km elevational gradient on Mt. Kilimanjaro, we quantify cross-taxon consensus in diversity gradients and evaluate predictors of diversity from single taxa to a multi-taxa community level. While single taxa show complex distribution patterns and respond to different environmental factors, scaling up diversity to the community level leads to an unambiguous support for temperature as the main predictor of species richness in both plants and animals. Our findings illuminate the influence of taxonomic coverage for models of diversity gradients and point to the importance of temperature for diversification and species coexistence in plant and animal communities.

Take time to smell the frogs: vocal sac glands of reed frogs (Anura: Hyperoliidae) contain species-specific chemical cocktails

Males of all reed frog species (Anura: Hyperoliidae) have a prominent, often colourful, gular patch on their vocal sac, which is particularly conspicuous once the vocal sac is inflated. Although the presence, shape, and form of the gular patch are well-known diagnostic characters for these frogs, its function remains unknown. By integrating biochemical and histological methods, we found strong evidence that the gular patch is a gland producing volatile compounds, which might be emitted while calling. Volatile compounds were confirmed by gas chromatography–mass spectrometry in the gular glands in 11 species of the hyperoliid genera Afrixalus, Heterixalus, Hyperolius, and Phlyctimantis. Comparing the gular gland contents of 17 specimens of four sympatric Hyperolius species yielded a large variety of 65 compounds in species-specific combinations. We suggest that reed frogs might use a complex combination of at least acoustic and chemical signals in species recognition and mate choice.