THEORETICAL AND EMPIRICAL-EXAMINATION OF DENSITY-DEPENDENT SELECTION

The development of theory on density-dependent natural selection has s een a transition from very general, logistic growth-based models to th eories that incorporate details of specific life histories. This trans ition has been justified by the need to make predictions that can then be tested experimentally with specific model systems like bacteria or Drosophila. The most general models predict that natural selection sh ould increase density-dependent rates of population growth. When trade -offs exist, those genotypes favored in low-density environments will show reduced per capita growth rates under crowded conditions and vice versa for evolution in crowded environments. This central prediction has been verified twice in carefully controlled experiments with Droso phila. Empirical research in this held has also witnessed a major tran sition from field-based observations and conjecture to carefully contr olled laboratory selection experiments. This change in approach has pe rmitted crucial tests of theories of density-dependent natural selecti on and a deeper understanding of the mechanisms of adaptation to diffe rent levels of population crowding. Experimental research with Drosoph ila has identified several phenotypes important to adaptation, especia lly at high larval densities. This same research revealed that an impo rtant trade-off occurs between competitive ability and energetic effic iency.