Local–regional species richness relationships are linear at very small to large scales in west-central Pacific corals

If local communities are saturated with species, the relationship between local and regional species richness [the local species richness (LSR)–regional species richness (RSR) relationship] is predicted to become increasingly curvilinear at more local spatial scales. This study tested whether the LSR–RSR relationship for coral species was linear or curvilinear at three local scales across the west-central Pacific Ocean, along a regional biodiversity gradient that includes the world's most diverse coral assemblages. The local scales comprised transects 100–2 m apart, sites 103–4 m apart and islands 104–6 m apart. The LSR–RSR relationship was never significantly different from linear at any scale. When the Chao1 estimator was used to predict true RSR and LSR, all relationships were also strongly linear. We conclude that local assemblages are open to regional influences even when the local scale is very small relative to the regional scale, and even in extraordinarily rich regions

Local and regional patterns in the community structure of corals

Community ecologists now recognize that to understand patterns of biodiversity, there is an urgent need to synthesize large-scale phenomena with local processes. This demands a multi-scale or hierarchical approach. We have begun a multi-scale study of the composition and relative abundances of corals along the pacific diversity gradient, from Indonesia to French Polynesia. Our goals are to examine how local diversity responds to variation in the size of the regional species pool, and to quantify the relative variation in community composition at different scales (ie. among adjacent zones, sites, islands and regions). So far, we have sampled 52 sites on 14 islands within four regions (PNG, the Solomon Islands, Samoa, and French Polynesia), a total of 1,560 x 10m transects. Most variation in diversity and community structure occurs at the smallest and largest scales - among depth zones (the reef flat, crest and slope) and among geographic regions - compared to adjacent sites and islands that are much more homogeneous. Surveys of juvenile corals reveal major differences in the underlying dynamics of different regions. For example, over half of the coral recruits in PNG and the Solomon Islands belong to genera that are absent entirely in Samoa and French Polynesia. Widespread species typically vary in abundance among regions by an order of magnitude or more, highlighting the need to quantify biogeographical patterns using ecological as well as taxonomic data

Patch-level facilitation fosters high-Andean plant diversity at regional scales

Aim: Local effects of ecosystem engineers on biodiversity can scale up to the landscape level, stressing the importance of ecological processes as determinants of species richness at larger spatial scales. In harsh environments, cushion plants often act as ecosystem engineers given their ability to buffer extreme abiotic conditions, thus providing unique and more favorable niches for the establishment of less stress-tolerant plant species. We assessed if facilitation by cushion plants influences patterns of plant diversity at increasing spatial scales. Location: Northern Patagonian Andes, Argentina. Methods: Based on plant species records within and outside cushions, we compared plant diversity in the presence and absence of cushions at the community, mountain and regional scale. Specifically, observed and estimated numbers of species occurring in either cushion plants or in the surrounding open areas were compared with the species numbers of the open areas. Results: The presence of cushion plants significantly increased species richness at all spatial levels analyzed. At the patch level, a higher number of species was recorded growing within cushion plants than in open area plots of similar size. Consistently, hypothetical communities lacking cushion plants showed significantly lower species richness than observed communities with cushion plants. These differences in species richness at patch and community scales increased with altitude, hence facilitation by cushion plants became more important at higher elevations. Moreover, according to asymptotic non-parametric estimators, cushion plants could increase overall regional species richness up to 40%. Conclusions: Our findings suggest that about one third of the high-Andean flora of the region owes its presence to the existence of nursing plants, defying the view that abiotic factors alone are enough to fully determine species occurrences at large spatial scales. This study provides evidence that local-scale ecological processes can be crucial in promoting and maintaining biodiversity at any spatial scale.Fil: Gavini, Sabrina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Ezcurra, Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Aizen, Marcelo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin