Multitaxonomic Diversity Patterns along a Desert Riparian–Upland Gradient

Justin Wright,Candan U Soykan,Juliet C Stromberg,Christine Hass,David A Simmons,William J D Patterson,John L Sabo,Leslie Ries,L Arriana Brand

doi:10.1371/journal.pone.0028235

Justin Wright, Candan U Soykan + Show 7 more

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https://doi.org/10.1371/journal.pone.0028235

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Abstract

Riparian areas are noted for their high biodiversity, but this has rarely been tested across a wide range of taxonomic groups. We set out to describe species richness, species abundance, and community similarity patterns for 11 taxonomic groups (forbs & grasses, shrubs, trees, solpugids, spiders, scarab beetles, butterflies, lizards, birds, rodents, and mammalian carnivores) individually and for all groups combined along a riparian–upland gradient in semiarid southeastern Arizona, USA. Additionally, we assessed whether biological characteristics could explain variation in diversity along the gradient using five traits (trophic level, body size, life span, thermoregulatory mechanism, and taxonomic affiliation). At the level of individual groups diversity patterns varied along the gradient, with some having greater richness and/or abundance in riparian zones whereas others were more diverse and/or abundant in upland zones. Across all taxa combined, riparian zones contained significantly more species than the uplands. Community similarity between riparian and upland zones was low, and beta diversity was significantly greater than expected for most taxonomic groups, though biological traits explained little variance in diversity along the gradient. These results indicate heterogeneity amongst taxa in how they respond to the factors that structure ecological communities in riparian landscapes. Nevertheless, across taxonomic groups the overall pattern is one of greater species richness and abundance in riparian zones, coupled with a distinct suite of species.

Highlights

Riparian zones are generally recognized as important for biodiversity conservation [1,2,3]; a general understanding of diversity patterns in riparian landscapes has yet to be achieved
Due to data availability we focused on two comparisons, riparian versus upland zones and river floodplain versus river terrace habitat types
Taxon-Level Analyses – Habitat Types When comparing individual habitat types (FP, river terraces (RT), NS, FS), six taxa had a trend of higher Mau Tau rarefied richness in the river floodplain habitat type, four taxa had a trend of higher rarefied richness in the river terrace habitat type, one taxon, solpugids, showed a trend of higher rarefied richness in the NS habitat type, and one taxon, lizards, had high estimates in RT and NS habitat types (Figure 3)

Summary

Introduction

Riparian zones are generally recognized as important for biodiversity conservation [1,2,3]; a general understanding of diversity patterns in riparian landscapes has yet to be achieved. A recent meta-analysis detected significant heterogeneity in effect sizes—here defined as differences in species richness between riparian and adjacent uplands—across the studies it considered [11] These contrasting results may stem from the design of most riparian–upland gradient studies that measure the species richness of one taxonomic group along a single riparian–upland gradient. Sabo et al [11] considered the importance of geographic location and taxonomy by contrasting richness patterns in wet versus dry climates and between studies done on animals versus plants They found no difference in effect size—as defined above— between studies in wet and dry regions, suggesting that across species, climate alone does not drive riparian–upland gradients in species richness. Few studies have documented patterns of species richness across the same riparian–upland transition for a representative suite of taxonomic groups

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