Effect of habitat degradation on competition, carrying capacity, and species assemblage stability

Abstract

Changes in species’ trophic niches due to habitat degradation can affect intra‐ and interspecific competition, with implications for biodiversity persistence. Difficulties of measuring species’ interactions in the field limit our comprehension of competition outcomes along disturbance gradients. Thus, information on how habitat degradation can destabilize food webs is scarce, hindering predictions regarding responses of multispecies systems to environmental changes. Seagrass ecosystems are undergoing degradation. We address effects of Posidonia oceanica coverage reduction on the trophic organization of a macroinvertebrate community in the Tyrrhenian Sea (Italy), hypothesizing increased trophic generalism, niche overlap among species and thus competition and decreased community stability due to degraded conditions. Census data, isotopic analysis, and Bayesian mixing models were used to quantify the trophic niches of three abundant invertebrate species, and intra‐ and interspecific isotopic and resource‐use similarity across locations differing in seagrass coverage. This allowed the computation of (1) competition strength, with respect to each other and remaining less abundant species and (2) habitat carrying capacity. To explore effects of the spatial scale on the interactions, we considered both individual locations and the entire study area (“‘meadow scale”). We observed that community stability and habitat carrying capacity decreased as P. oceanica coverage declined, whereas niche width, similarity of resource use and interspecific competition strength between species increased. Competition was stronger, and stability lower, at the meadow scale than at the location scale. Indirect effects of competition and the spatial compartmentalization of species interactions increased stability. Results emphasized the importance of trophic niche modifications for understanding effects of habitat loss on biodiversity persistence. Calculation of competition coefficients based on isotopic distances is a promising tool for describing competitive interactions in real communities, potentially extendible to any subset of ecological niche axes for which specimens’ positions and pairwise distances can be obtained.

Changing Isotopic Food Webs of Two Economically Important Fish in Mediterranean Coastal Lakes with Different Trophic Status

“…The high selectivity for polychaetes in the highly eutrophicated lake could be due to the facilitated capture of these preys and their good contribution to the energy supply of their predators compared to other aquatic invertebrates [66][67][68]. Changes in the feeding choices of the two fish species resulted in increased interspecific niche overlap, suggesting that eutrophication may have strong bottom-up effects on interspecific interactions [69,70].…”

Predicting the ecological impacts of an alien invader: Experimental approaches reveal the trophic consequences of competition

“…The same process was followed to determine the mean interspecific isotopic dissimilarity (MND ij ) per species and treatment, except the first step was to calculate the mean isotopic distance of each individual fish from their sympatric species (ND ij ) (Calizza et al, 2017). The same process was followed to determine the mean interspecific isotopic dissimilarity (MND ij ) per species and treatment, except the first step was to calculate the mean isotopic distance of each individual fish from their sympatric species (ND ij ) (Calizza et al, 2017).…”

“…higher values indicate increased dissimilarity. The same process was followed to determine the mean interspecific isotopic dissimilarity (MND ij ) per species and treatment, except the first step was to calculate the mean isotopic distance of each individual fish from their sympatric species (ND ij ) (Calizza et al, 2017).…”

The role of habitat configuration in shaping animal population processes: a framework to generate quantitative predictions

“…Developing such mechanistic knowledge is critical as natural animal populations face increasingly rapid changes in their habitats, which have ecological and evolutionary consequences. For instance, habitat change can affect the magnitude of competition (Calizza et al, 2017) and the spread dynamics of pathogens (Bloomfield et al, 2020), information (Betts et al, 2008), or genes (Keller and Largiader, 2003).…”