Author: Vadim Alexandrovich KaratayevPublisher:
ISBN: 9781658413640
Category :
Languages : en
Pages :
Book Description
When qualitatively distinct, alternatively stable ecological states occur under the same environmental conditions, disturbance can lead to abrupt and persistent ecosystem shifts. Whilst theoretically possible in simple models of many systems, empirical evidence for this phenomenon remains limited to relatively simple ecosystems. In other systems, feedback loops that underlie this dynamic might weaken due to environmental variation and species differences, reducing the relevance of alternative stable states. In this dissertation, I resolve the ecological processes that can lead to alternative stable states in heterogeneous ecosystems. In interconnected systems where environments differ among local communities, the local relevance of alternative stable states might erode as immigration overwhelms local feedbacks. In Chapter 1, I quantify how interconnectedness affects the relevance of alternative stable states using dynamical models of California rocky reef communities that incorporate observed environmental stochasticity and feedback loops. My models demonstrate the potential for localized kelp- or urchin-dominated alternative states despite high interconnectedness because feedbacks affect dispersers as they settle into local communities. Regionally, such feedbacks affecting settlement can produce a mosaic of alternative stable states that span local (10-20km) scales despite the synchronizing effect of long-distance dispersal. These predictions reflect observed scales of community states in California rocky reefs and suggest how alternative states co-occur in many marine and terrestrial systems with settlement feedbacks. Within local communities, environmental variation might limit alternative stable states to fine-scale mosaics rather than larger patches. Temperate rocky reefs exemplify each of patterned communities, local environmental variation, and feedbacks in urchin behavior. Specifically, urchins can reduce grazing activity when kelp are abundant either in local stands that attract predators and cause physical abrasion or across entire reefs when fronds detached from kelp canopies subsidize urchin diets. By fitting dynamical models to large-scale reef surveys, in Chapter 2 I show that reef-scale feedbacks can create reef-scale, alternatively stable kelp- and urchin-dominated states at 37% of sites in California. In New Zealand, local feedbacks limit this phenomenon to fine-scale mosaics at 3-8m depths with moderate wave stress on kelp, with distinct single stable states in exposed shallows and sheltered, deeper areas. My results also highlight that grazer behavior can regulate community patterning. In food webs, demographic heterogeneity and specialized interactions among species might also dissipate the feedbacks that create alternative stable states. In Chapter 3 I develop a general model of consumer-resource interactions with either specialized feedbacks where individual resources become unpalatable at high abundance or aggregate feedbacks where overall resource abundance reduces consumer recruitment. I then quantify how species differences in demography affect the potential for either feedback to produce alternatively stable consumer- or resource-dominated states. I find that alternative stable states can be relevant to multispecies food webs with aggregated feedbacks, greater interconnectedness, and lower species differences. Where specialized feedbacks occur, I highlight a greater potential for the sudden collapse of many species at low stress levels when vulnerable species uniquely contributing to guild persistence collapse. Simpler models that aggregate species into groups omit this reduced resilience under low redundancy in species roles.