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The species–time relationship (STR) describes how the species richness of a community increases with the time span over which the community is observed. This pattern has numerous implications for both theory and conservation in much the same way as the species–area relationship (SAR). However, the STR has received much less attention and to date only a handful of papers have been published on the pattern. Here we gather together 984 community time-series, representing 15 study areas and nine taxonomic groups, and evaluate their STRs in order to assess the generality of the STR, its consistency across ecosystems and taxonomic groups, its functional form, and its relationship to local species richness. In general, STRs were surprisingly similar across major taxonomic groups and ecosystem types. STRs tended to be well fit by both power and logarithmic functions, and power function exponents typically ranged between 0.2 and 0.4. Communities with high richness tended to have lower STR exponents, suggesting that factors increasing richness may simultaneously decrease turnover in ecological systems. Our results suggest that the STR is as fundamental an ecological pattern as the SAR, and raise questions about the general processes underlying this pattern. They also highlight the dynamic nature of most species assemblages, and the need to incorporate time scale in both basic and applied research on species richness patterns. [ABSTRACT FROM AUTHOR]

This article presents a case study of the long-term change in complex communities. Increased development and associated impacts to natural environments are consequences of the growth of human populations. As a result, several approaches and statistical designs for assessing the effects of impacts on natural communities have been proposed. Before-After, Control-Impact (BACI) overcomes the lack of spatial replication of the impact by using repeated sampling of control and impact sites through time to provide replication within the "before" and "after" periods. Despite the potential power and usefulness of BACI designs there are few published examples for any ecosystem, because of the need for repetitive sampling over a long period of time using the same sampling design, which is expensive and difficult to achieve in a commercial and regulatory framework. In one marine application, a BACI design was used in southern California to detect the effects in a sand-dominated kelp habitat of a thermal discharge released subtidally through diffusers from a power plant.

One of the most commonly predicted effects of global ocean warming on marine communities is a poleward shift in the distributional boundaries of species with an associated replacement of cold-water species by warm-water species. However, these types of predictions are imprecise and based largely on broad correlations in uncontrolled studies that examine changes in the distribution or abundances of species in relation to seawater temperature. Our study used an 18-year sampling program in intertidal and subtidal habitats and before-after, control-impact analyses. We show that a 3.5°C rise in seawater temperature, induced by the thermal outfall of a power-generating station, over 10 years along 2 km of rocky coastline in California resulted in significant community-wide changes in 150 species of algae and invertebrates relative to adjacent control areas experiencing natural temperatures. Contrary to predictions based on current biogeographic models, there was no trend toward warmer-water species with southern geographic affinities replacing colder- water species with northern affinities. Instead, the communities were greatly altered in apparently cascading responses to changes in abundance of several key taxa, particularly habitat-forming subtidal kelps and intertidal foliose red algae. Many temperature-sensitive algae decreased greatly in abundance, whereas many invertebrate grazers increased. The responses of these benthic communities to ocean warming were mostly unpredicted and strongly coupled to direct effects of temperature on key taxa and indirect effects operating through ecological interactions. [ABSTRACT FROM AUTHOR]