Ecosystem interactions within populations

At an ecosystem level, complex interactions within and between populations and nonlinear biological dynamics may create a latency period between the exposure event and certain effects (Landis et al. 1996 Matthews et al. 1996), particularly when considering the indirect effects of chemical stress. Populations of organisms may be affected by toxicants in an indirect way when a reduction or elimination... 

However, as the material leaves the pipe and enters the ecosystem, it is almost immediately affected by both the biotic and abiotic components of the receiving system. All of the substrate and medium heterogeneity as well as the inherent temporal and spatial characteristics of the biota affect the incoming material. In addition to the state of the system at the time of pollution, the history of the environment as contained in the genetic makeup of the populations plus additional stressors in the past or present all impact the chemical-ecosystem interaction. The goal of the exposure analyses is to quantify the occurrence and availability of the stressor within the ecosystem. 

Organisms evolving under aimual temperature cycles and in environments with varying temperatures spatially have incorporated thermal cues in reproductive behavior, habitat selection, and certain other features which act at the population level. Thus, the balance of births and mortaUties, which determines whether a species survives, is akin to the metaboHc balance at the physiological level in being dependent upon the match, within certain limits, to prescribed temperatures at different times of year. At the ecosystem level, relationships among species, eg, predators, competitors, prey animals, and plant foods, are related to environmental temperatures in complex ways. Many of these interactions are poorly understood. 

Ecotoxicology Is concerned with die toxic effects of chemical and physical agents in living organisms, especially on populations and communities within defined ecosystems it includes transfer pathways of these agents and their interaction with the environment. 

Figure 6. Conceptual model of how the key ecosystem level processes involving CDOM (Figure 1) and the molecular, organism, population, and community level effects of temperature and UV (Figure 5) can be integrated within the context of climate change and ozone depletion. This makes lakes particularly good models for examining the interactive effects of temperature and UVR on natural ecosystems.

---