Habitat Selection, the Included Niche, and Coexistence in Plant-Specialist Frogs from Madagascar

Unexpected diversity and co-occurrence of phytotelmic frogs (Guibemantis) around Andasibe, one of the most intensively surveyed amphibian hotspots of Madagascar, and descriptions of three new species

The area around the Malagasy village of Andasibe, which includes Analamazaotra-Mantadia National Park as well as other protected areas, is characterized by very species-rich and well-studied communities of animals and plants, but new species are still regularly discovered. Three species of phytotelmic frogs of the subgenus Pandanusicola in the genus Guibemantis are known from this area, G. flavobrunneus, G. liber, and G. pulcher. Further Pandanusicola frogs from this area have been provisionally assigned to G. bicalcaratus or G. albolineatus, pending detailed taxonomic review. During preliminary exploration of the ecology of these specialized frogs that live and reproduce in the leaf axils of Pandanus screw pines, we noticed the syntopic presence of two differently colored and differently sized Pandanusicola in Andasibe that could not be unambiguously assigned to any known species. A genetic screening revealed that these correspond to yet two further species in the area. Based on our data, seven species of Pandanusicola occur in Andasibe and nearby forests: (1) G. liber, the only non-phytotelmic species of the subgenus in the region; (2) G. flavobrunneus which is the largest species and characterized by a diagnostic yellowish brown dorsal pattern; (3) G. pulcher, characterized by translucent-green color with purplish brown spotting not observed in any other species in the area; (4) G. methueni, a brownish species usually lacking contrasted dorsolateral bands that differs from the other species in the area by emitting a characteristic trill-like advertisement call series (rather than clicks or chirps) and according to our data is widespread along Madagascars east coast; as well as three new species: (5) G. ambakoana sp. nov., a brownish species, typically with contrasted incomplete light dorsolateral bands and with single click-like advertisement calls; (6) G. vakoa sp. nov., a species that is equally brownish but lacks contrasted light dorsolateral bands and that has single click-like advertisement calls of very short duration; and (7) G. rianasoa sp. nov., a species that is smaller sized and has less distinct femoral glands than all the others, and emits a short series of soft chirp-like advertisement calls. All these species are genetically highly distinct, with >5% uncorrected pairwise distances in the mitochondrial 16S rRNA gene, and lack of haplotype sharing in two nuclear-encoded genes. The co-occurrence of seven Pandanusicola frogs in a relatively small geographic area is unprecedented in Madagascar and calls for in-depth studies of a possible differentiation in habitat use and life history.

A new species of Pandanus-dwelling frog from northern Madagascar related to Guibemantis pulcher

Populations of phytotelmic frogs from northern Madagascar assigned to Guibemantis (Pandanusicola) pulcher are known to differ genetically from populations further south in the eastern rainforest belt of the island, but to date, their status has not been analyzed in depth. We combined molecular genetic data with an examination of color pattern to clarify the taxonomy of these frogs. DNA sequences of both mitochondrial and nuclear-encoded genes were consistently differentiated between the northern populations and those occurring further south. Uncorrected pairwise distance in the 16S rRNA gene was 3.7‒4.3% and thus at a level usually characterizing distinct frog species in Madagascar. Furthermore, the northern specimens were characterized by more and smaller purplish-brown spots on their green dorsal surface, and a less distinct brown patch on the flanks. Although fully conclusive evidence for the species status of the northern lineage from bioacoustic differences, sympatric occurrence or narrow hybrid zone is currently lacking, such species-level distinctness is currently the most likely hypothesis. We therefore name the northern populations as Guibemantis (Pandanusicola) pulcherrimus sp. nov. The new species is known from Makira (type locality) and Bemanevika, and specimens morphologically assignable to this taxon have also been recorded from Masoala, Marojejy and Anjanaharibe-Sud.

Empirical Evidence for the Rescue Effect from a Natural Microcosm

Ecological theory predicts that populations which receive immigrants are less vulnerable to extinction than those that do not receive immigrants (the "rescue effect"). A parallel but opposite process may also exist, where emigration increases the risk of local extinction (the "abandon-ship effect"). Using a natural microcosm of plant-specialist frogs from Madagascar, empirical evidence for both processes is provided. Populations receiving immigrants were less extinction-prone than those without immigration, and those populations losing individuals through emigration were more extinction-prone than those in which no emigration occurred. The number of immigrants and emigrants was also elevated and depressed (respectively) in patches that did not go extinct. These data provide some of the first definitive empirical evidence for the rescue effect and provide suggestive initial data on the abandon-ship effect. Both of these processes may be important to understanding the dynamics of populations.

Coexistence of Two Closely Related Cyprinid Fishes (Hemiculter bleekeri and Hemiculter leucisculus) in the Upper Yangtze River, China

Species coexistence is one of the most important concepts in ecology for understanding how biodiversity is shaped and changed. In this study, we investigated the mechanism by which two small cyprinid fishes (H. leucisculus and H. bleekeri) coexist by analyzing their niche segregation and morphological differences in the upper Yangtze River. Morphological analysis indicated that H. leucisculus has posteriorly located dorsal fins, whereas H. bleekeri has a more slender body, bigger eyes, longer anal fin base, and a higher head. Niche segregation analysis showed spatial and trophic niche segregation between these two species: on the spatial scale, H. leucisculus was more widely distributed than H. bleekeri, indicating that H. leucisculus is more of a generalist in the spatial dimension; on the trophic scale, H. bleekeri had a wider niche than H. leucisculus. Therefore, these two species adopt different adaptation mechanisms to coexist

Bird functional diversity decreases with time since disturbance: Does patchy prescribed fire enhance ecosystem function?

Animal species diversity is often associated with time since disturbance, but the effects of disturbances such as fire on functional diversity are unknown. Functional diversity measures the range, abundance, and distribution of trait values in a community, and links changes in species composition with the consequences for ecosystem function. Improved understanding of the relationship between time since fire (TSF) and functional diversity is critical given that the frequency of both prescribed fire and wildfire is expected to increase. To address this knowledge gap, we examined responses of avian functional diversity to TSF and two direct measures of environmental heterogeneity, plant diversity, and structural heterogeneity. We surveyed birds across a 70-year chronosequence spanning four vegetation types in southeast Australia. Six bird functional traits were used to derive four functional diversity indices (richness, evenness, divergence, and dispersion) and the effects of TSF, plant diversity and structural heterogeneity on species richness and the functional diversity indices were examined using mixed models. We used a regression tree method to identify traits associated with species more common in young vegetation. Functional richness and dispersion were negatively associated with TSF in all vegetation types, suggesting that recent prescribed fire generates heterogeneous vegetation and provides greater opportunities for resource partitioning. Species richness was not significantly associated with TSF, and is probably an unreliable surrogate for functional diversity in fire-prone systems. A positive, relationship between functional evenness and structural heterogeneity was comnon to all vegetation types, suggesting that fine-scale (tens of meters) structural variation can enhance ecosystem function. Species more common in young vegetation were primarily linked by their specialist diets, indicating that ecosystem services such as seed dispersal and insect control are enhanced in more recently burnt vegetation. We suggest that patchy prescribed fire sustains functional diversity, and that controlled use of patchy fire to break up large expanses of mature vegetation will enhance ecosystem function.