Non‐interactive fish communities in the coastal streams of North‐western France

Abstract

Summary 0[ Spatial patterns of freshwater _sh species at regional and local scales were inves! tigated to explore the possible role of interspeci_c interactions in in~uencing dis! tribution and abundance within communities occupying coastal streams of North! Western France[ 1[ Nine sites from nine streams situated in the same biogeographical region were sampled annually over the 5!year period from 0889 to 0884[ 2[ Similar habitats "sites# with richer regional colonization pools exhibited pro! portionally richer local communities in terms of number of species\ total density and total biomass of individuals[ Furthermore\ no negative relationships were found between density and biomass of each of the most common species and local species richness[ 3[ Results of dynamic regression models "applied to the above!mentioned species# suggest an absence of strong competition between all pairs of species[ 4[ The evidence on lack of density compensation for species!poor communities and absence of perceptible interspeci_c competition between species suggest that the communities studied are non!interactive[ 5[ Two main explanations can be advanced[ First\ the local abundance of species in the communities studied could be determined through di}erential responses to unpredictable environmental changes\ rather than through biological interactions[ Second\ as a result of historical events\ the communities studied are reduced in congeneric species which can limit\ in turn\ the in~uence of interspeci_c competition in structuring these communities[ 6[ These results underline the strong in~uence of regional processes in shaping local riverine _sh communities and minimize the possible in~uence of species interactions in governing these communities[ Key!words] density compensation\ _sh assemblages\ interspeci_c interactions\ local species richness\ regional species richness[ Journal of Animal Ecology "0887# 56\ 361Ð373

Effects of natural and anthropogenic environmental changes on riverine fish assemblages: a framework for ecological assessment of rivers

“…Relative to this point, results of different studies previously detailed above show that local and regional fish communities are usually not saturated with species and are capable of supporting greater number of species if the pool of potential colonists and the rate of colonization from that pool was increased by species introduction (Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998;Gido and Brown, 1999). These results strongly suggest that competition does not set the species saturation level in the assemblages studied and thus that competition is not a major force structuring these fish assemblages.…”

“…competition, predation, disturbance) were the focus of studies seeking to explain local fish assemblage structure (Schlosser, 1995), emphasis on the role of regional processes has increased as some studies have demonstrated their pervasive role in shaping local assemblages Whittier et al, 1988;Hugheny and Paugy, 1995;Hugueny et al, 1997;Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998). Consequently, complete answers for the explanation of local fish assemblage richness and structure must address the relative importance of large-scale processes, which determine the species available to occur locally and small-scale processes, which should limit the number of species that actually occur locally (Angermeier and Winston, 1998).…”

“…Patterns and processes observed in local fish assemblages are not only determined by local mechanisms acting within assemblages, but also result from processes operating at larger spatial scales (Hugueny and Paugy, 1995;Hugueny et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998, Jackson et al, 2001). The richness and structure of local fish assemblages has been linked to factors ranging from geomorphology and climate (Nelson et al, 1992;Whittier et al, 1988;Matthews and Matthews, 2000;Tejerina-Garro, 2001), to richness of regional species pool (Hugueny and Paugy, 1995;Hugueny et al, 1997;Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998;Gido and Brown, 1999).…”

“…The richness and structure of local fish assemblages has been linked to factors ranging from geomorphology and climate (Nelson et al, 1992;Whittier et al, 1988;Matthews and Matthews, 2000;Tejerina-Garro, 2001), to richness of regional species pool (Hugueny and Paugy, 1995;Hugueny et al, 1997;Belkessam et al, 1997;Angermeier and Winston, 1998;Oberdorff et al, 1998;Gido and Brown, 1999). Concerning this last relationship (local/regional richness) the emerging pattern is that few fish assemblages are trully saturated (Hugueny andPaugy 1995, Hugueny et al, 1997;Belkessam et al, 1997;Oberdorff et al, 1998). For example, working on local fish assemblages of coastal streams of North-Western France found that these assemblages were unsaturated with species and with individuals and that inter-annual changes in populations were not strongly affected by densities of co-occurring species.…”

Variabilité à moyen terme des peuplements de poissons des cours d'eau bas-normands

“…En effet, chacune des espèces qui compose les peuplements étudiés réagit de façon différentielle aux variations environnementales (différence dans : les périodes de ponte et de recrutement, la distribution sur le gradient vertical, les habitats, la taille des individus et leurs vagilités...) et contribue de la sorte à faire augmenter la variabilité du peuplement à mesure que l'on augmente la durée du suivi. Par ailleurs, à l'échelle locale, les peuplements de poissons des cours d'eau semblent dépendre, en partie, de processus qui s'opèrent à l'échelle régionale (HUGUENY et PAU G Y, 1995 ;BELKESSAM et al, 1997 ;OBERDORFF et al, 1998). …”