A Matter of Scale: Historical and Environmental Factors Structure Anuran Assemblages from the Upper Madeira River, Amazonia

Abstract

Biogeographical history and current ecological interactions have usually been addressed separately to explain the spatial distribution of patterns of biodiversity. In this study, we evaluated the integrated effects of biogeographical and environmental factors in structuring the diurnal amphibian anuran assemblages of the upper Madeira River, southwestern Amazonia. We used a sampling design involving 98 standardized units, distributed across seven locations covering both banks of the river's course in the state of Rondônia, Brazil. We conducted searches for frogs in three campaigns between February 2010 and February 2011, aiming to: (1) evaluate the effect of the Madeira River as a biogeographic barrier at the species‐assemblage level, and (2) test the influence of seven environmental variables (vegetation structure, vegetation cover, soil nutrients, soil structure, slope, elevation, and distance from the river bank) on the spatial structure of the frog assemblages, separately on each riverbank. Thirteen species of diurnal frogs were recorded, six of which were restricted to one of the river margins. Multivariate analysis of variance indicated a significant effect of the river as a barrier. Multiple regression analyses suggested that the environmental variables structuring frog assemblages differ on either side of the river. We found that both historical elements (on a regional scale) and environmental factors (at a local scale) shaped the occurrence and distribution of frog species in the study area.

The combined influence of riverine barriers and flooding gradients on biogeographical patterns for amphibians and squamates in south‐eastern Amazonia

“…The presence of cryptic species may still cause a bias in the observed patterns, but to minimize this problem we employed a large sampling effort to collect primary data and used an integrative species identification approach. Changes in assemblage composition occurred both on the opposite banks of the Tapajós and in forests with different flooding regimes, indicating that both ecological (flooding regimes) and historical (riverine barriers) factors have influenced the structure of assemblages, as reported for other Amazonian regions (Gascon et al ., ; Dias‐Terceiro et al ., ). In addition, some functional groups were more affected by riverine barriers than others.…”

“…As well as these variables, distance to streams (Fraga et al ., ; Menin et al ., ), forest type (Gascon et al ., ; Pavan, ; Garda et al ., ) and leaf‐litter morphology (Menin et al ., ) all influence amphibian and squamate distribution. However, the overall difficulty researchers have faced in detecting general patterns suggests that the relationship between ecological factors and distributional patterns is idiosyncratic (Dias‐Terceiro et al ., ).…”

“…Simões et al ., ; Souza et al ., ; Fouquet et al ., ). Only a few studies have addressed variation in assemblage structure, and those that do exist show that both historical and ecological factors have helped shape species’ distributions within these groups at different scales (Ávila‐Pires, ; Gascon et al ., ; Ron, ; Dias‐Terceiro et al ., ). The dearth of assemblage‐level approaches for investigating these relationships has been caused primarily by the lack of basic knowledge regarding the species’ distributions, which has resulted from the focus of studies on a few accessible areas, lack of standardization and short‐term sampling (Azevedo‐Ramos & Galatti, ).…”

Morphological diversity and community organization of desert anurans

“…At broader spatial scales (i.e., macrohabitat and mesohabitat), the composition and distribution of frog assemblages has been linked to abiotic factors, such as topographic and edaphic gradients, climate, and vegetation type (Duellman 1999, Dias-Terceiro et al, 2015Dayton et al, 2004;Menin et al, 2007;Dias-Terceiro et al, 2015). At the habitat scale, anuran assemblage structure is influenced by edaphic gradients, species-specific responses attributed to prey abundance or suitable breeding sites (Menin et al, 2007;Dias-Terceiro et al, 2015;Watling, 2005.…”

“…At the habitat scale, anuran assemblage structure is influenced by edaphic gradients, species-specific responses attributed to prey abundance or suitable breeding sites (Menin et al, 2007;Dias-Terceiro et al, 2015;Watling, 2005. Frogs of the Chihuahuan Desert region exhibit strong associations between species presence and the soil and vegetation type (Dayton et al, 2004;Boeing et al, 2013).…”