Multitaxonomic Diversity Patterns along a Desert Riparian–Upland Gradient

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

Richness by zone for each taxonomic group.

<p>Mau Tau rarefied richness values (±95% confidence intervals) for the eight taxa sampled in both riparian and upland zones along the upper San Pedro River. The only values that had non-overlapping 95% confidence intervals were birds in riparian and upland zones.</p

Abundance by zone for each taxonomic group.

<p>Bootstrapped abundance estimates (±95% confidence intervals) for the eight taxa sampled in both riparian and upland zones along the upper San Pedro River.</p

Kruskal-Wallis test results (p-values) for between-habitat type or between-zone effect size differences based on the biological groups described in the Supporting Information: Table S1.

<p>Kruskal-Wallis test results (p-values) for between-habitat type or between-zone effect size differences based on the biological groups described in the Supporting Information: <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028235#pone.0028235.s007" target="_blank">Table S1</a>.</p

Map of the upper San Pedro River.

<p>The river is located in the Chihuahuan Desert of southeastern Arizona, USA. Note the extent of the San Pedro Riparian National Conservation Area, shaded gray.</p

Richness and abundance meta-analysis results.

<p>Rip-Up = the difference in richness or abundance between riparian and upland zones; FP-RT = the difference in richness or abundance between river floodplain and river terrace habitat types. Results from the meta-analyses examining the difference in species richness and species abundance between riparian and upland zones (n = 8 groups) and between river floodplain and river terrace habitat types (n = 11 groups). The figure shows mean weighted effect sizes with associated upper and lower 95% confidence intervals.</p

Abundance by habitat type for each taxonomic group.

<p>Bootstrapped abundance estimates (±95% confidence intervals) in four different habitat types for the eleven taxa sampled along the upper San Pedro River (abbreviations as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028235#pone-0028235-t001" target="_blank">Table 1</a>).</p

Richness by habitat type for each taxonomic group.

<p>Mau Tau rarefied richness values (±95% confidence intervals) in four different habitat types for the eleven taxa sampled along the upper San Pedro River (abbreviations as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028235#pone-0028235-t001" target="_blank">Table 1</a>). The only values that had non-overlapping 95% confidence intervals were solpugids in NS and FP habitat types.</p

Observed and expected beta diversity values based on the additive partitioning method of Veech et al. [26].

<p>*The probability of observing the measured values of beta diversity is based on the randomization of individuals among samples.</p