Sistemi consumatori-risorse come modelli per ecosistemi disturbati

Disturbances are ubiquitous in ecosystems, and are characterized by widely different intensity and frequency. At one end of this spectrum stand exogenous pulse perturbations, which are related to sudden events of large magnitude which cause ecosystems to become displaced from their previously stable state. At the other end, organisms in complex ecosystems invariably experience fluctuating pressures due to endogenous ecological processes, which may derive, for example, from demographic stochasticity. In this thesis, we address both these scenarios of ecological disturbance. We investigate first the impact of disturbances on forest ecosystems by examining transient population dynamics in a controlled experiment carried out in a tropical rainforest. We model the mean species abundance with a simple consumer-resource model, which is then extended into two multi-species frameworks for community dynamics: a neutral model, which emphasizes the ability of any species to recover independently of the others; and a non-neutral one, where species interactions play an important role in reconstructing ecosystem's structure and patterns. The results indicate that, while both frameworks accurately describe correlation functions and mean-variance relations, the non-neutral model more effectively captures community structure as revealed by an evenness indicator. This suggests that interspecific interactions significantly influence the ecosystem's ability to respond to disturbances, providing deeper insights into the recovery dynamics of forest ecosystems. We then move on to study the effects of endogenous ecological fluctuations on community structure and diversity. The competitive exclusion principle (CEP), stating that the number of coexisting species in an ecosystem is upper-bounded by the number of resources, is a key result of MacArthur's model of resource competition. In contrast, many ecosystems exhibit coexistence of a large number of species competing for a handful of resources, with most species being rare and few being abundant. The study of credible mechanisms that can help explain these aspects of ecosystem structure is a rich but still active line of research. Here, we investigate how correlated temporal fluctuations of feeding rates affect the coexistence of competing species'. To this end, we consider a stochastic consumer-resource model, where metabolic strategies (i.e., the rates of resource consumption) are modeled by colored noise. We find that time-changing metabolic strategies, as opposed as fixed values, lead to community structures that more closely align to those observed in nature, and to the breaking of the CEP. Further, the CEP is maximally broken when competition strength is intermediate. Our framework connects the extreme cases of highly variable and constant metabolic strategies, showing how species rarity emerges as a vestigial signature of the breaking of the CEP.