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Adaptive Radiation and Evolutionary Convergence in Neotropical Cichlids Kirk Winemiller, Rodney Honeycutt, Hernán López-Fernández & Melanie Stiassny
The cichlid fishes are one of the most diverse and ecologically important
families of fishes inhabiting freshwaters of the planet. Decades of
extensive research on the cichlid fishes inhabiting the great rift lakes
of East Africa have provided science with one of the clearest examples of
evolution leading to the generation ecological diversity. In the Western
Hemisphere, the family Cichlidae ranges from Texas to
Pattern, Process and Scale in the Food Web Paradigm: Moving on the path from Abstraction to Prediction Kirk O. Winemiller and Craig A. Layman Like any scientific endeavor, research on food webs advances on three interacting fronts: description, theory, and model testing (experimentation). Development of food web theories (models) and their applications are greatly outpacing advances in the descriptive and experimental arenas. Although this state of affairs is not unexpected in an immature scientific discipline, it results in inefficient development of understanding. Why have empirical components lagged behind theoretical developments? We propose that unresolved issues of scale and resolution have hindered empirical research. Resolution of three basic features of food webs is required. First, the spatial and temporal boundaries of a community food web are always arbitrary, and it should be recognized that any food web is a module within a larger system. Objective methods for defining and quantifying nested modules are needed. Second, great variation is observed in the treatment of food web components, ranging from species life stages to functional groups containing diverse taxa. In most empirical studies, these components have been invoked a posteriori rather than a priori. We propose that species populations are the only natural food web components, because populations are evolutionary units with dynamics that are independent of membership in a guild or functional group. Third, food web links must be accompanied by some measure of interaction strength or magnitude. Theoretical studies have firmly established that interaction strength and adaptive foraging determine food web dynamics. Consequently, food webs created with unchanging binary links (present or absent) are irrelevant. Moreover, empirical research is needed to establish the degree to which direct mutualism (e.g., pollination, seed dispersal) contributes to food web dynamics. A fourth critical issue is the degree to which food web structure and dynamics are driven by environmental factors, especially climatic and landscape factors. We briefly discuss four alternative models of food web structure, and contend that available empirical evidence is insufficient to evaluate them. Despite the fact that a deficient empirical knowledge base is the main hurdle to scientific advancement, pressing natural resource problems require application of existing models to inform management. We propose a multi-faceted empirical approach for long-term field studies as means to advance understanding of food webs. Click [here] to view a powerpoint presentation given at the 3rd decadal food web symposium in Giessen, Germany, November 2003.
Life history strategies, population regulation, and their implications for fisheries management Kirk O. Winemiller Life history theories seek to explain the evolution of organism traits as adaptive responses to environmental variation. Life history theories also make qualitative predictions about population responses to natural and human-induced disturbances at different spatial and temporal scales. A model involving three primary life history strategies, or syndromes, predicts population responses to patterns of natural and anthropogenic disturbance at variable scales of time and space. The model provides a general means to predict a priori the types of populations that should have high or low demographic resilience, production potential, and conformity to density-dependent regulation. For certain species and habitats, the model challenges the notion that population dynamics can be predicted based on density-dependent responses to environmental carrying capacity. Periodic (long-lived species with high fecundity) and opportunistic (small, short-lived species with high reproductive effort) strategists should conform poorly to projections from models that assume significant density dependence over long time scales. The model's implications for fisheries management are explored relative to sustainable harvest, endangered species conservation, exotic species, habitat suitability indices, supplemental stocking of marine fishes, artificial reefs, and marine reserves. The degree of compensatory reserve, population resilience, and conformation to equilibrium assumptions of population dynamics should vary predictably based on life history attributes, which provides guidance for management, especially when detailed information is lacking.
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Updated Wednesday March 01, 2006 |
Argentina, and
species display a very broad array of ecological, morphological, and
behavioral traits. Unfortunately,
evolutionary relationships among major groups of Neotropical cichlids are
incompletely resolved, making modern quantitative assessment of ecological
diversification impossible.
radiation) in this important group
of fishes.