Short‐term climatic trends affect the temporal variability of macroinvertebrates in California ‘Mediterranean’ streams

Abstract

1. Long-term studies in ecology are essential for understanding natural variability and in interpreting responses to disturbances and human perturbations. We assessed the longterm variability, stability and persistence of macroinvertebrate communities by analysing data from three regions in northern California with a mediterranean-climate. During the study period, precipitation either increased or decreased, and extreme drought events occurred in each region. 2. Temporal trends in precipitation resulted in shifts from 'dry-year' communities, dominated by taxa adapted to no or low flow, to 'wet-year' communities dominated by taxa adapted to high flows. The abundance of chironomid larvae was an important driver of community change. Directional change in community composition occurred at all sites and was correlated with precipitation patterns, with more dramatic change occurring in smaller streams. 3. All communities exhibited high to moderate persistence (defined by the presence/ absence of a species) and moderate to low stability (defined by changes in abundance) over the study period. Stability and persistence were correlated with climatic variation (precipitation and El Niñ o Southern Oscillation) and stream size. Stability and persistence increased as a result of drought in small streams (first-order) but decreased in larger streams (second-and third-order). Communities from the dry season were less stable than those from the wet-season. 4. This study demonstrates the importance of long-term studies in capturing the effects of and recovery from rare events, such as the prolonged and extreme droughts considered here.

High Variability Is a Defining Component of Mediterranean-Climate Rivers and Their Biota

“…These small community changes, however, have been significantly related to comparing wet-with-wet and dry-with-dry years [21]. Wet years are dominated by species adapted to high flows, whereas dry years include a higher proportion of lentic species [85]. Inter-annual community changes can interact with seasonal changes, resulting in differential effects under varying times of onset and the duration of the wet and dry seasons.…”

Responses of macroinvertebrate communities to long‐term flow variability in a Sonoran Desert stream

“…Climate plays an obvious role as a driver of hydrologic pattern, and variability in rainfall and temperature has major consequences for the disturbance regime and habitat template of aquatic ecosystems (Firth & Fisher, 1992;Heino et al, 2008). Furthermore, multiyear studies in streams have shown that climate-driven changes in hydrology may substantially affect the structure of aquatic macroinvertebrate communities (Bêche & Resh, 2007;Durance & Ormerod, 2007;Magalhães et al, 2007;Power et al, 2008), and projected reductions in river discharge are expected to result in the widespread loss of species (Xenopoulos & Lodge, 2006). Because of this sensitivity to flow regime, aquatic ecosystems and their communities are recognized as useful sentinels for a suite of climate and land-use changes that have the potential to alter hydrologic routing in both the terrestrial and aquatic sectors of a landscape (Williamson et al, 2008).…”

Temporal variations in macroinvertebrate communities from the tributaries in the Three Gorges Reservoir Catchment, China

“…These changes greatly influence the timing of emergence, reproduction, growth and development of many aquatic macroinvertebrates and, in turn, influence the seasonal replacement of organisms [54]. Thus, among the numerous environmental conditions, discharge and water temperature are often considered the important factors that contribute to the marked seasonality in assemblage composition [7,24,25,27,55]. According to the theory "intermediate disturbances", the season variations in discharge and water temperature enhance species richness and maintain maximum species density.…”

“…In climate regions with relatively high seasonal environmental variability or complex climatic patterns, the macroinvertebrate fauna was always characterized by the stochastic, unstable community structure in aquatic systems; within these systems, organisms had fast growth and high colonization capacity, and showed strong temporal variation or seasonality [31,55]. For instance, the species richness and abundance were significantly higher during the dry season than during the wet season in tropical streams [22,58].…”