Analysing the distance decay of community similarity in river networks using Bayesian methods

The distance decay of community similarity (DDCS) is a pattern that is widely observed in terrestrial and aquatic environments. Niche-based theories argue that species are sorted in space according to their ability to adapt to new environmental conditions. The ecological neutral theory argues that community similarity decays due to ecological drift. The continuum hypothesis provides an intermediate perspective between niche-based theories and the neutral theory, arguing that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive to stochastic exclusion. We assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index in riparian plant communities. We assessed the importance of neutral processes using network distances and flow connection and of niche-based processes using Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to determine which perspective is best supported by the results. We used dataset composed of 338 vegetation censuses from eleven river basins in continental Portugal. We observed that changes in Sorensen indices were associated with network distance, flow connection, Strahler order difference and precipitation difference but to different degrees. The results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.

Distance decay of community similarity in river networks: a Bayesian approach

The distance decay of community similarity (DDCS) is a pattern that is widely observed in both terrestrial and aquatic environments. There are three major perspectives for explaining the DDCS. Niche-based theories argue that as environmental conditions change, species are sorted according to their ability to adapt to new environmental conditions and habitats. The ecological neutral theory argues that community similarity decays due to ecological drift. Finally, the continuum hypothesis argues that niche and neutral factors are at the opposite ends of a continuum that ranges from competitive exclusion to stochastic exclusion. Most studies on the DDCS have been conducted on terrestrial ecosytems, and there are few data for riparian plant communities in riparian ecosystems. Here we assessed the association between niche-based and neutral factors and changes in community similarity measured by Sorensen’s index. As neutral variables, we used network distances and flow connection, and as niche-based variables, we selected Strahler order differences and precipitation differences. We used a hierarchical Bayesian approach to assess which of these three perspectives best supported the results. We used a high-quality dataset composed of 338 vegetation censuses conducted in eleven river basins along a sizeable environmental gradient in continental Portugal. We observed that changes in Sorensen indices were associated with all four covariates but to different degrees. Overall, the results suggest that community similarity changes are associated with environmental and neutral factors, supporting the continuum hypothesis.

Influence of diversion power stations on riparian plant communities along Dicun stream China

This article used three diversion power stations with different operating years along Dicun stream of the source of Jiulong River to study the riparian plant community and discussed the impact of power station development on riparian plants. The results showed that:(1)There were significant differences in the plant diversity of herbs, shrubs and trees among all sample plots in the study area (P < 0.05).(2) The species number of the second and third diversion power stations with longer operation time was larger than that of the fourth diversion power station with short operation time.(3) The water-borne plants were concentrated in the herb layer in the influence area of the diversion power station, and the Richness, Shannon- Wiener, Simpson and Pielou indexes of water-borne plants in the study area were significantly different (P < 0.05). (4) The appearance of diversion power station leaded to the change of environmental factors, and the river depth and flow rate had significant positive correlation with the diversity index of riparian plants and water water-borne plants (P < 0.05). In general, with the increase of the operation time of the power station, the surrounding riparian plant will form a new stable community.