Elevational diversity patterns of rodents differ between wet and arid mountains

Abstract

Aim: Patterns of species richness along elevation gradients vary with geographic and environmental factors but evidence for similar variation in functional and phylogenetic diversity remains scarce. Here, we provide the most comprehensive evaluation to date of elevational gradients in taxonomic, functional, and phylogenetic diversity of rodents -one of the most ecologically diverse groups of mammals -and test the effects of latitude and aridity on their variation for the first time.Location: Forty-nine mountains on five continents. Time period: Contemporary.Major taxa studied: Rodents (Rodentia). Methods:We compiled elevational distributions of 374 rodent species across 49 elevational gradients. For each gradient, we quantified -in 100-m elevational bins -rodent species richness and functional and phylogenetic richness, evenness, and dispersion, and their species richness-corrected equivalents. To assess how rodent diversity varies with elevation, we fitted a series of models that included elevation, average latitude, and aridity of each mountain system while accounting for variation in study design and sampling effort.Results: A common mid-elevational peak in species richness among mountains contrasts with functional and phylogenetic diversity pattern variation (model shape and slope) explained by the aridity at a mountain's base. Specifically, we find that functional and phylogenetic richness and dispersion decline with elevation in wet mountain systems but increase with elevation in arid mountains. Main conclusions:In this first comparative analysis of mammal functional and phylogenetic elevational gradients, we find that the decoupling of each from species richness is particularly pronounced in arid regions. Wet-mountain lowlands and aridmountain highlands harbour the most functionally and phylogenetically diverse rodent communities, indicating that water availability is a strong environmental filter in structuring diversity of small mammals on mountain gradients. High regularity of species distances within assemblages supports a constant role for competition across all elevations and niche expansion in elevations with greater species richness.

Decomposing niche components reveals simultaneous effects of opposite deterministic processes structuring alpine small mammal assembly

“…Over the last few decades, considerable progress has been made toward a better understanding community assembly along environmental gradients, from local to global scales. A prevalent perspective asserts that communities in harsher habitats are usually structured by habitat filtering (Cavender-Bares et al, 2009;Read et al, 2018;Zhang et al, 2020) because survival under stressful environmental conditions often requires specialized traits (Gohli and Voje, 2016;Kohli et al, 2022;Tang et al, 2022). These findings are foundational hypotheses for investigating community assembly in mountain areas characterized by rapid environmental changes along elevational gradients.…”

Elevation filters bat, rodent and shrew communities differently by morphological traits

“…Moving up the elevational gradient, rainfall tends to decrease in wet regions, while in dry mountains, due to orographic rainfall, it may increase at mid-elevation, creating a "hump-shaped" species richness distribution likely as a direct response to water scarcity (Kohli et al, 2022;McCain, 2007;Weier et al, 2017). Regardless of the ecosystem, the extreme conditions, including large fluctuations in daily minimum and maximum temperatures, at higher elevations, will inevitably curtail species richness at the highest elevations (McCain, 2007).…”

“…Variation in species richness along elevational gradients seems to differ according to the two types of mountains (Kohli et al., 2022; McCain, 2007). Wet mountains, those situated in regions receiving high rainfall in the lowlands around the mountain itself, are surrounded by high species richness in the neighbouring lowlands whereas arid mountains are surrounded by low species richness.…”

“…Wet mountains, those situated in regions receiving high rainfall in the lowlands around the mountain itself, are surrounded by high species richness in the neighbouring lowlands whereas arid mountains are surrounded by low species richness. Moving up the elevational gradient, rainfall tends to decrease in wet regions, while in dry mountains, due to orographic rainfall, it may increase at mid‐elevation, creating a “hump‐shaped” species richness distribution likely as a direct response to water scarcity (Kohli et al., 2022; McCain, 2007; Rahbek, Borregaard, Colwell, et al., 2019; Weier et al., 2017). Regardless of the ecosystem, the extreme conditions, including large fluctuations in daily minimum and maximum temperatures, at higher elevations, will inevitably curtail species richness at the highest elevations (McCain, 2007).…”

Multiple dimensions of phylogenetic diversity are needed to explain the complex aboveground–belowground diversity relationships

“…For beta diversity at the richness dimension, such a correlation suggests that if both plant and microbial communities are more dissimilar then they are both exhibiting substantial compositional turnover such that different sites have many new phylogenetic branches. A positive relationship for the divergence dimension suggests that phylogenetically distantly related plants promote the co‐occurrence of phylogenetically distantly related microbes, which would be the signal of coevolution between plants and microbes (Bitomský et al 2022, Kohli et al 2022). For the beta diversity level, such correlation indicates that if plant and microbial communities are both more phylogenetically dissimilar then turnover between sites is occurring deeper in the phylogeny, likely reflecting an underlying selection gradient.…”