1. Interspecific competition is commonly defined as the reciprocal negative effects of two species on the population growth rate of the other species, and models of competition examine effects on population dynamics (e.g., a12, one form of the competition coefficient, is the effect of one individual of species 2 on dN1/N1dt, where N1 is the abundance (or density of species 1). However, most field (or lab) experiments examine competition by examining effects on the individual-level (e.g., effects on somatic growth, habitat use, diet, survival, reproduction), not the population level (e.g., via effects on dN1/N1dt).
2. Many studies of effects of pollutants are ultimately concerned with effects that pollutants have on the distribution and abundance of species. Yet, most studies of pollutant effects are toxicological investigations that focus on individual level effects (e.g., changes in behavior, growth, fecundity) or sub-individual effects (e.g., biochemical changes, such as the induction of certain enzymes).
3. Global warming is a very important issue being investigated by ecologists in many diverse ways. One question that concerns scientists is whether plants will be able to "buffer" the earth from increased discharges of CO2. To that end, many physiological plant ecologists have attempted to determine if primary production (photosynthetic rate, plant growth, biomass accrual) increases in response to elevated CO2. Recent experimental work (in which potted plants or very small plots (of several square meters) are exposed to high [CO2]) suggests that plants grown under elevated CO2 exhibit, on average, a 30-40% increase in production. It can be argued that these data are actually inadequate to predict the extent to which plants may buffer the earth from increased emissions of CO2, because the data come from short-term physiological responses, rather than longer-term responses, including acclimation, species compositional shifts, and changing levels of limitation imposed by other resources and consumers.
4. Trade-offs are common and are believed to underlie many of the patterns in natural systems (e.g., modes of reproduction, foraging behavior, etc.). For example, the pumpkinseed sunfish is a specialized molluscivore and my colleagues and I have argued that an increased ability to crush snails is associated with a cost associated with feeding on soft-bodied prey (e.g., snail crushing requires large molariform pharyngeal jaws that may make it difficult to handle and/or capture small elusive prey, such as amphipods). We can induce changes in morphology in sunfish (by changing their diet) and we have documented that "crushing" fish can not only crush a wider range of snails (a benefit), but that they also require more time to handle soft-bodied prey (a cost). We have argued that this trade-off probably has affected the evolution of feeding morphology in sunfish. This argument is very incomplete however. Costs and benefits should be defined with respect to how they affect fitness. We've defined them only with regard to their effects on components of foraging behavior (e.g., "fraction of attacked snail that get crushed" or "handling time").
The Challenge: In each of these cases (or others you are familiar with), please think about 1) why these "schisms" exist, and 2) how we can "scale-up" these findings to eliminate the apparent schism between the questions that interest us and the data that we collect? For example, how can we take information on toxicological effects on individual physiology and use it to understand or predict effects on population dynamics? Please think about empirical approaches, as well as those that might require a modeling approach.
osenberg@zoo.ufl.edu