Document: COU-3-52-49

Can functional redundancy in primary producer assemblages and variability in consumer populations buffer communities from multiple stressors?

RICHMOND, C.E.* ¹, D.L.BREITBURG ¹ and K.A.ROSE ²

Academy of Natural Sciences Estuarine Research Center, St. Leonard, MD 20685 USA ¹
Coastal Fisheries Institute, Louisiana State University, LA USA ²

Abstract:
Environmental conditions can affect a consumer directly through changes in survival, fecundity, behavior, and metabolic activities, or indirectly through effects on lower trophic levels. An assemblage with multiple species performing similar functional roles may buffer the system from stressor effects, due to the differential sensitivities of functionally redundant members. We were interested in the direct effects of stressors on a primary consumer as well as how the community composition of its food source influences the capacity of an assemblage to buffer against stressors. To examine the relationships between functional redundancy, buffering from stressors, and stressor effects, we modeled a primary producer (phytoplankton) assemblage with different degrees of functional redundancy, and then exposed the assemblage to common estuarine stressors (nutrient loading and trace metals). The consumer species in this model was the planktonic copepod Acartia tonsa, an ubiquitous and important primary consumer in estuarine systems. We enabled A. tonsa to experience both the direct effects of stressors on growth and development, and the indirect effects of shifts in the phytoplankton community it preys upon. The copepods were modeled using an individual-based approach with variability in sizes and bioenergetic characteristics, resulting in a range of individual types and possible responses to environmental conditions. Individual variability played an important role in A. tonsa's direct responses to stressors. Functional redundancy in the primary producer assemblage provided some protection for copepods from the indirect effects of stressors, provided that at least one species in a functional group was either insensitive to the stressor or had a complimentary response to those species negatively impacted. If a species within a functional group were negatively impacted, A. tonsa experienced the additional indirect effects of stressors, ultimately impacting copepod vital rates, population dynamics, and the characteristics of the surviving population. These results highlight the importance of understanding both direct and indirect effects of stressors on natural systems, as well as the role of community composition in determining impacts on higher trophic levels.

Keywords:

This abstract is being presented at: 3:30 PM in session:
Oral Session #11: Trophic Cascades.