This research focuses on the ecological and evolutionary significance of flow regime to macroinvertebrate communities in tropical dry forest streams of Costa Rica. Pristine tropical watersheds are ideal sites for testing the effects of flow on stream communities because the confounding effects of seasonality in temperature and photoperiod and high silt and sediment load associated with most temperate streams are absent, and many pristine small streams with perennial flow regimes are available for study. The research will quantify macroinvertebrate community structure and the life history characteristics and production of all widespread and common species of macroinvertebrates in riffle habitat of six perennial streams. The study will focus on temporal changes in these parameters in response to prolonged (6 month) periods of both constant (dry season) and elevated (wet season) flow as well as to short-term flood flaws during the wet season. The central hypothesis of the study is that: stream macroinvertebrate communities are not oversaturated with species (in the absence of disturbance) and may be capable of withstanding long periods of abiotic stability without loss of diversity, i.e. there is no "paradox of the stream benthos". The principal objectives of this research project are to: (1) quantify seasonal variation in the relative abundance and species composition of macroinvertebrates and test the utility of flow as a covariate for explaining this variability; (2) document the extent of seasonality in macroinvertebrate life histories and evaluate sesonality as an adaptation to flow regime; (3) evaluate the relative importance of storms in explaining seasonal variability in macroinvertebrate community structure (4) assess the role of spatial scale (i.e. patch size) in studies of benthic community succession; and (5) evaluate the role of disturbance in maintaining the diversity of stream communities.
