Trophic-dynamic considerations in relating species diversity to ecosystem resilience

Complexity in the networks of interactions among and between the living and abiotic components forming ecosystems confounds the ability of ecologists to predict the economic consequences of perturbations such as species delet ions in nature. Such uncertainty hampers prudent decision making about wher e and when to invest most intensively in species conservation programmes. D emystifying ecosystem responses to biodiversity alterations may he best ach ieved through the study of the interactions allowing biotic communities to compensate internally for population changes in terms of contributing to ec osystem function, or their intrinsic functional redundancy. Because individ ual organisms are the biologically discrete working components of ecosystem s and because environmental changes are perceived at the scale of the indiv idual, a mechanistic understanding of functional redundancy will hinge upon understanding how individuals' behaviours influence population dynamics in the complex community setting. Here, I use analytical and graphical modell ing to construct a conceptual framework for predicting the conditions under which varying degrees of interspecific functional redundancy can be found in dynamic ecosystems. The framework is founded on principles related to fo od web successional theory, which provides some evolutionary insights for m echanistically linking functional roles of discrete, interacting organisms with the dynamics of ecosystems because energy is the currency both for eco logical fitness and for food web commerce. Net productivity is considered t he most contextually relevant ecosystem process variable because of its soc ioeconomic significance and because it ultimately subsumes all biological p rocesses and interactions. Redundancy relative to productivity is suggested to manifest most directly as compensatory niche shifts among adaptive fora gers in exploitation ecosystems, facilitating coexistence and enhancing eco system recovery after disturbances which alter species' relative abundances , such as extinctions. The framework further explicates how resource scarci ty and environmental stochasticity ma!: constitute 'ecosystem legacies' inf luencing the emergence of redundancy by shaping the background conditions f or foraging behaviour evolution and, consequently, the prevalence of compen sator!: interactions. Because it generates experimentally testable predicti ons for a priori hypothesis testing about when and where varying degrees of functional redundancy ale likely to be found in food webs, the framework m ay be useful for advancing toward the reliable knowledge of biodiversity an d ecosystem function relations necessary for prudent prioritization of cons ervation programmes. The theory presented here introduces explanation of ho w increasing diversity can have a negative influence on ecosystem sustainab ility by altering the environment for biotic inter actions and thereby chan ging functional compensability among biota - under particular conditions.