Biotic interactions help explain variation in elevational range limits of birds among Bornean mountains

Abstract

Aim Physiological tolerances and biotic interactions along habitat gradients are thought to influence species occurrence. Distributional differences caused by such forces are particularly noticeable on tropical mountains, where high species turnover along elevational gradients occurs over relatively short distances and elevational distributions of particular species can shift among mountains. Such shifts are interpreted as evidence of the importance of spatial variation in interspecific competition and habitat or climatic gradients. To assess the relative importance of competition and compression of habitat and climatic zones in setting range limits, we examined differences in elevational ranges of forest bird species among four Bornean mountains with distinct features. Location Bornean mountains Kinabalu, Mulu, Pueh and Topap Oso. Taxon Rain forest bird communities along elevational gradients. Methods We surveyed the elevational ranges of rain forest birds on four mountains in Borneo to test which environmental variables—habitat zone compression or presence of likely competitors—best predicted differences in elevational ranges of species among mountains. For this purpose, we used two complementary tests: a comparison of elevational range limits between pairs of mountains, and linear mixed models with naïve occupancy as the response variable. Results We found that lowland species occur higher in elevation on two small mountains compared to Mt. Mulu. This result is inconsistent with the expectation that distributions of habitats are elevationally compressed on small mountains, but is consistent with the hypothesis that a reduction in competition (likely diffuse) on short mountains, which largely lack montane specialist species, allows lowland species to occur higher in elevation. The relative influence of competition changes with elevation, and the correlation between lower range limits of montane species and the distribution of their competitors was weaker than in lowland species. Main conclusions These findings provide support for the importance of biotic interactions in setting elevational range limits of tropical bird species, although abiotic gradients explain the majority of distribution patterns. Thus, models predicting range shifts under climate change scenarios must include not only climatic variables, as is currently most common, but also information on potentially resulting changes in species interactions, especially for lowland species.

Bird species co‐occurrence patterns in an alpine environment supports the stress‐gradient hypothesis

“…Here, we examined patterns of species co-occurrence over a 20-year period in bird communities of the Swiss Alps applying a pluralistic analytical approach. Our results do not evince a prominent role of competition as structuring agent in the studied assemblages, which is in accordance with that reported in other mountain systems (Bornean mountains: Boyce et al 2019, Burner et al 2020, Cantabrian mountains: Bastianelli et al 2017eastern Himalayas: Elsen et al 2017, but see Surya and Keitt 2019). However, we must stress that competitive interactions are difficult to infer using observational data.…”

Occupancy patterns and upper range limits of lowland Bornean birds along an elevational gradient

“…Counterintuitive responses to increasing temperatures can also result from changing competitive interactions (Tingley, Koo, Moritz, Rush, & Beissinger, ) as distributions and abundance of some species change. Temperature does appear to affect the range limits of montane forest birds in Borneo (Burner et al, In Revision), many of which appear to have shifted over time (Harris et al, ).Tropical montane species, whose habitat is slightly more secure from logging and development because of the difficulty and expense of working in mountains, are probably in greater danger from climate change because of limited space for upward movement. Additional work on the physiology and competitive interactions of both lowland and montane tropical species would help to refine these conclusions.…”

“…Evidence that competition can limit species ranges on mountain slopes is available from other regions (Elsen, Tingley, Kalyanaraman, Ramesh, & Wilcove, ; Jankowski et al, ; Romdal & Rahbek, ). Similarly, based on comparisons of elevational ranges of bird species and their potential competitors (from the same genus or foraging guild) on Bornean mountains, there is evidence that competitive interactions likely play a role in determining range limits of both lowland and montane species (Burner et al, In Revision). However, we found that few lowland‐montane species pairs differed in co‐occurrence scores from the null predictions, even when both pair‐members were in the same genus or foraging guild.…”

“…In this case lowland species near their upper range limits would be clustered with one another in these patches. Alternatively, if competition with montane species limits ranges, then the upper edge of lowland species distributions should vary according to the occurrence of the montane competitor (Burner et al, In Revision).…”

A trade‐off between latitude and elevation contributes to explain range segregation of broadly distributed cave‐dwelling spiders

“…General theory predicts that segregation along spatial gradients should be particularly visible in highly dispersive species, such as birds (Auer & King, 2014; Burner et al., 2020; Graham et al., 2009), insofar as the effect of antagonistic interactions require the species to be in contact (that is, some sort of spatial proximity). Conversely, the effect of competition is often found to be of limited importance in driving the distribution of poorly dispersive species, such as subterranean ones (Mammola et al., 2020; Zakšek et al., 2019).…”