Microclimate species diversity, and food web interactions along a desert riparian-upland gradient.

摘要

The San Pedro watershed in southeastern Arizona is an internationally recognized "hotspot" for mammals, hosting one of the richest assemblages in the United States. High species richness in this system can be attributed to geographic position, ecological gradients, and non-equilibrium processes. The transition from near-river forests to upland desert scrub habitats offers the opportunity to study microclimate and species diversity patterns along ecological gradients, and how those patterns affect processes such as food web interactions across habitat boundaries.; Surprisingly few studies have explored riparian-upland gradients in microclimate, even though they are thought to affect ecological patterns and processes. Along the San Pedro River, vegetation structure and distance-from-river influence microclimate variables such as air and soil temperature, relative humidity, and wind speed. Moreover, both these factors also influence variability in microclimate along the gradient. The relative importance of distance-from-river and vegetation structure depends on the microclimate variable under consideration, time of year, and scale of investigation.; This study documented local and regional patterns in species diversity, including measures of richness, evenness, and abundance patterns for nine taxonomic groups along the riparian-upland gradient. Species richness is similar among habitat types along the gradient, as is species evenness, at both local and regional scales. Abundance, on the other hand, is similar among habitats at the local scale, but higher in riparian habitats at the regional scale. Dispersal limitation does not seem to play an important role in structuring ecological communities at the scales considered herein, whereas habitat affinity appears to be quite important.; Increased awareness of spatiotemporal variation in species interactions has motivated the study of food web dynamics at the landscape level. This study tested whether mammalian carnivores spill over from productive, near-river habitats into adjacent, desert-scrub habitats; and if they do, to document the effects of this spillover on rodent community structure. The results indicate that carnivores track seasonally-abundant resources across the landscape. In turn, rodent population dynamics track seasonal shifts in carnivore habitat use but not resource availability, suggesting that spillover predation structures small mammal communities in near-river, desert-scrub habitats.