Effects of habitat size and isolation on species immigration–extinction dynamics and community nestedness in a desert river system

Abstract

Summary Habitat fragmentation is one of the major causes of local and regional species extinctions in freshwater ecosystems. To predict future trends in community composition, and the potential sequence of extinctions due to fragmentation of the river continuum, it is important to understand how habitat size and isolation affect the dynamics of species immigrations and extinctions and patterns of abundance and occupancy. We examined fish immigration and extinction rates, and abundance and occupancy patterns, in relation to habitat isolation, size and variability in the Rio Grande and its tributaries in the Trans‐Pecos region of Texas, U.S.A. Our results indicated that as habitat isolation increased in tributaries, fish immigration and extinction rates and riverine species abundances decreased. Fish assemblages showed significant nested subset patterns across the study sites, and the influence of habitat size and isolation on the nested subset patterns varied with spatial scale. Certain non‐native fish taxa were idiosyncratic, reducing the strength of the nested subset pattern. The high temporal species turnover in connected habitats was related to the movement of riverine fish species between the mainstem and mouths of tributaries. High persistence of spring‐adapted species decreased extinction rate in isolated habitats. Increasing the spatial scale of the study system probably resulted in an increased ability to detect dispersal limitation between the mainstem and its tributaries. Large, deep pools decreased local extinction of certain native fish taxa in upstream tributaries. The deviation from the nested subset pattern was attributed to the unique regional occupancy of non‐native fish taxa that could be associated with their artificial introduction into this system. Our results suggest that increased habitat fragmentation by human activities can accelerate the regional extinction of certain native fish taxa and the dominance of ecologically tolerant, possibly non‐native fish, leading to a decline in regional diversity.

Hydrologic connectivity driven natural stream fish assemblages in mountain streams in the Yangtze River basin: implications for stream fish conservation in monsoonal East Asia

“…The headwater and small stream assemblages are inclined towards local extinction and recolonization while larger mainstem habitat could serve as refugium and provide an important source of immigrants for subsequent recolonization following a disturbance. Our result thus supports the findings of Osborne & Wiley (1992) and other studies that have implicated the relative importance of immigration-extinction dynamics in structuring stream fish assemblages (Angermeier & Schlosser, 1989;Osborne & Wiley, 1992;Gotelli & Taylor, 1999;Taylor & Warren, 2001;Hitt & Angermeier, 2008;Miyazono & Taylor, 2013).…”

“…Additionally, locations with higher HPD usually have lower riparian vegetation cover. Increased anthropogenic disturbances could cause a shift from sensitive species to more tolerant, often nonnative species (Vila-Gispert et al, 2002;Brasher, 2003;Sutela & Vehanen, 2010;Miyazono & Taylor, 2013;Gao et al, 2015). Although HPD was highly correlated with DDC in this case (Table 5), two factors had a different the influence on the fish assemblages.…”

“…Miyazono & Taylor (2013) found that as isolation from the mainstem increased, immigration rate and species richness decreased in the tributary localities in a desert river system, the Rio Grande and its tributaries in the Trans-Pecos region of Texas, USA. In the intermittent streams in north-western Zimbabwe of Africa, the connectivity of the habitats during periods of high flow provides colonizing habitats for both the upstream and downstream assemblages (Kadye & Chakona, 2012).…”

Scaling fish metacommunities in stream networks: synthesis and future research avenues

“…For example, Roberts and Hitt (2010) found temporally more variable fish communities in downstream than in upstream reaches in four of their five examined streams, which run counter with the stream continuum model. Miyazono and Taylor (2013) confirmed these findings, since they found more variable communities in downstream reaches due to the ingress and egress of riverine species at the mouths of tributaries and relatively stable communities in upstream isolated reaches, where community dynamics were determined by local species. This pattern fits the adventitious stream model which predicts greater temporal species turnover in downstream than upstream reaches (Roberts and Hitt 2010).…”

Do diel variations in stream fish assemblages depend on spatial positioning of the sampling sites and seasons?

“…Increasing complexity and size of the habitat downstream, differential rates of immigration and extinction are some of the most possible factors responsible for this typical longitudinal pattern (Schlosser 1982, Power et al 1988, Miyazono & Taylor 2013. We found significantly higher species richness and collected more individuals (on average) at Site 1 than at Site 2 suggesting preferential habitat use and maybe higher immigration and lower emigration rates at Site 1.…”