Partitioning the colonization and extinction components of beta diversity: Spatiotemporal species turnover across disturbance gradients

ABSTRACTChanges in species diversity often result from species losses and gains. The dynamic nature of beta diversity (i.e., spatial variation in species composition) that derives from such temporal species turnover, however, has been largely overlooked. Here, we disentangled extinction and colonization components of beta diversity by using the sets of species that went locally extinct and that newly colonized the given sites. We applied this concept of extinction and colonization beta diversity to plant communities that have been repeatedly measured in experimentally disturbed forests. We first found no difference in beta diversity across disturbance gradients when it was analyzed for communities at a single point in time. From this result, we might conclude that disturbance caused no impact on how species assemble across space. However, when we analyzed the extinction and colonization beta diversity, both measures were found to be significantly lower in disturbed sites compared to undisturbed sites. These results indicate that disturbance removed similar subsets of species across space, making communities differentiate, but at the same time induced spatially uniform colonization of new species, causing communities to homogenize. Consequently, the effects of these two processes canceled each other out. The relative importance of extinction and colonization components per se also changed temporally after disturbance. Analyses using extinction and colonization beta diversity allowed us to detect nonrandom dis- and re-assembly dynamics in plant communities. Our results suggest that common practices of analyzing beta diversity at one point in time can mask significant variation driven by disturbance. Acknowledging the extinction–colonization dynamics behind beta diversity is essential for understanding the spatiotemporal organization of biodiversity.

Monitoring fruit-feeding butterfly assemblages in two vertical strata in seasonal Atlantic Forest: temporal species turnover is lower in the canopy

To address how seasonality affects the richness and abundance of tropical insects, we compared the canopy and understorey communities of fruit-feeding butterflies in a seasonal Atlantic forest in south-eastern Brazil. Butterflies were sampled over 1 y using a standardized design with baited traps. A total of 2047 individuals in 69 species were recorded (1415 in the canopy, 632 in the understorey). Clear differences were found between canopy and understorey, with significantly higher butterfly abundances in the canopy. We observed two marked peaks of abundance and richness in both strata; one at the transition from dry to the wet seasons, and the other at the transition from wet to dry seasons. We found lower species turnover throughout the year in the canopy. We interpret this as evidence that temperature is more important than rainfall in explaining the yearly variation of abundance in vertical strata. The higher temperatures found in the canopy may allow butterflies to maintain activity in this stratum all year round, whereas the understorey is subject to colder temperatures, thus presenting a higher species turnover. These results improve our understanding of diversity gradients between evergreen and seasonal tropical forests, allowing insights into how climate and beta diversity gradients interact.

Temporal species turnover and plant community changes across different habitats in the Lake Engure Nature Park, Latvia

Simultaneous monitoring of vegetation dynamics in different ecosystems has been rarely conducted but can provide important insights into mechanisms of vegetation dynamics in relation to vegetation structure and patterns. We compared the herb layer dynamics, species turnover, and species-time relationships across different habitats in a 12-year period in the ILTER monitoring station of the Lake Engure Nature Park, Latvia. Temporal species turnover was defined as diference in species composition in a community between two times. Species-time relationships were assessed using a sliding window approach. Species richness, cumulative species richness, and diversity changed more in species-rich non-forest habitats than in forests. Species turnover was highly different among habitats, and was not associated with the stability of habitats, as reported from other studies. The species-time relationship of six habitats was much lower than that reported in the literature. This could be explained by latitudinal gradients in species diversity and temporal turnover. At higher latitudes both species diversity and turnover is lower, and the mentioned habitats represent typical boreal vegetation. Vegetation dynamics in acidic grassland, dune slack, fen, and dune forest were interpreted as fluctuations. Vegetation changes in moist forest, dry forest, and coastal grassland showed clear signs of succession (xerophytisation and overgrowing). Vegetation dynamics of the beach community exhibited features of both natural succession and anthropogenic fluctuation.

Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

<em>Abstract</em>.—Five conceptual models of longitudinal fish community organization in streams were examined: (1) niche diversity model (NDM), (2) stream continuum model (SCM), (3) immigrant accessibility model (IAM), (4) environmental stability model (ESM), and (5) adventitious stream model (ASM). We used differences among models in their predictions about temporal species turnover, along with five spatiotemporal fish community data sets, to evaluate model applicability. Models were similar in predicting a positive species richness–stream size relationship and longitudinal species nestedness, but differed in predicting either similar temporal species turnover throughout the stream continuum (NDM, SCM), higher turnover upstream (IAM, ESM), or higher turnover downstream (ASM). We calculated measures of spatial and temporal variation from spatiotemporal fish data in five wadeable streams in central and eastern North America spanning 34–68 years (French Creek [New York], Piasa Creek [Illinois], Spruce Run [Virginia], Little Stony Creek [Virginia], and Sinking Creek [Virginia]). All streams exhibited substantial species turnover (i.e., at least 27% turnover in stream-scale species pools), in contrast to the predictions of the SCM. Furthermore, community change was greater in downstream than upstream reaches in four of five streams. This result is most consistent with the ASM and suggests that downstream communities are strongly influenced by migrants to and from species pools outside the focal stream. In Sinking Creek, which is isolated from external species pools, temporal species turnover (via increased richness) was higher upstream than downstream, which is a pattern most consistent with the IAM or ESM. These results corroborate the hypothesis that temperate stream habitats and fish communities are temporally dynamic and that fish migration and environmental disturbances play fundamental roles in stream fish community organization.