Isolation vs. Extinction in the Assembly of Fishes in Small Northern Lakes

Abstract

To evaluate the roles of extinction and isolation in predicting richness and composition of fish assemblages in small forest lakes of Finland and Wisconsin, we analyzed data from 114 Finnish and 55 Wisconsin lakes 0.2–86.9 ha in area. Six isolation variables characterized properties of stream corridors, land barriers, and source pools of invading species; four extinction variables were related to habitat severity, lake area, and productivity. Two types of multivariate analyses were used: the nonparametric classification and regression trees (CART) and the parametric linear discriminant analysis (LDA). Both types of analyses showed that extinction variables were collectively more important than isolation variables in predicting richness and composition both in Finland and Wisconsin. We interpret that the greater importance of extinction vs. isolation results, not because isolation is unimportant, but because the probability of an arrival of a new species is much less than that of an extinction. Thus, the time after an extinction event before a subsequent invasion is long relative to the time after an invasion event before a subsequent extinction; consequently, fish assemblages sampled at a given point in time more likely represent the stamp of the extinctions than of the invasions. This conclusion was robust to the differences in the geomorphic settings and fish faunas of Finland and Wisconsin. However, the importance of individual isolation and extinction variables in determining richness and composition differed between the two regions, apparently more from differences in geomorphic settings than from differences in fish faunas. Influences of horizontal rather than vertical barriers over land and water were more apparent in Wisconsin, with its lower relief and higher incidence of lakes without stream connections; influences of the area of the nearest lake (representing the size of the available species pool) and stream gradient were more important in Finland, with its higher relief and higher incidence of lakes with stream connections. The importance of individual extinction variables also differed between the two regions, again reflecting differences in the geomorphic settings of the two lake districts and the strong influence that lake position in the landscape has in determining limnological features of the lake.

Lake connectivity and fish species richness in southern Brazilian coastal lakes

“…Patterns of fish species richness and composition in lakes are influenced by biogeographic and watershed scale factors, by local biotic and abiotic variables, by perturbation regime, and also by lake area and connectivity (Mandrak, 1995;Magnuson et al, 1998;Jackson et al, 2001;Olden et al, 2001;Sharma et al, 2011). Although habitat connectivity has received less attention in aquatic than in terrestrial ecology Heino & Muotka, 2006), recently its frequency in aquatic ecology studies has increased.…”

“…In aquatic systems, connectivity has been generally treated as a synonym of isolation and measured by the presence or absence of a structural connection, by its temporal persistence (time) and length (Magnuson et al, 1998;Olden et al, 2001;Zeug et al, 2005;Beisner et al, 2006;Heino & Muotka, 2006;Ö hman et al, 2006;Scheffer & Geest, 2006;Herwig et al, 2010;Miyazono et al, 2010), or by other measurements only indirectly related to the type of habitat along the connection (Tonn & Magnuson, 1982;Spens et al, 2007). However, in terrestrial ecosystems, connectivity is usually considered as an emergent property of species-landscape interactions (Taylor et al, 2006) representing ''the degree to which the landscape facilitates or impedes movement among resource patches'' (Taylor et al, 1993).…”

Seascape and metacommunity processes regulate fish assemblage structure in coastal wetlands

“…A preference for finer substrates has been observed previously for L. equulus in Australian tropical estuaries (Johnston & Sheaves 2007). This behaviour may relate to selective foraging for benthic invertebrates, which form a considerable proportion of their diet (Wilson & 199 Permanent freshwater body Estuary channel (Snodgrass et al 1996, Taylor 1997, Magnuson et al 1998 in tidal systems of similar topological configuration based on results of the present study. In the freshwater system, species and individuals are progressively filtered out along a gradient of isolation, illustrated by progressively lighter shades of blue in circles (patches) further away from the source pool.…”

“…Metacommunity concepts have been developed through empirical studies in fragmented freshwater wetlands (De Meester et al 2005, Logue et al 2011 and have provided greater insights into the processes driving fish community structure (Snodgrass et al 1996, Magnuson et al 1998). The balance between local and regional influences shifts, depending on the extent of inter-patch connectivity in a system.…”

“…infrequent hydrological connections, large inter-patch distances, low exchange of organisms), while in better connected systems (i.e. with frequent connections, proximate patches, high exchange of organisms), regional dispersal often masks local effects (Magnuson et al 1998, Brown & Swan 2010. A high influence of dispersal generally results in patterns of nestedness forming among patches (Snodgrass et al 1996, Taylor 1997, whereby assemblages of more isolated patches are subsets of those in better connected patches because of the filtering out of species and individuals with progressive isolation.…”