Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver–response relationships to develop conceptual models across ecosystems

Abstract

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed ‘beta diversity’) is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta‐analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mech...

Thermophilization and reshuffling of montane leaf beetle communities over a two‐decade period

“…Heterogeneity in range shifts among species has also driven changes in the spatial diversity pattern along the elevation gradient. The reduction in spatial turnover between the low and intermediate sites has caused biotic homogenization at the regional scale (sensu Rolls et al, 2023), as previously observed for other montane organisms (e.g., Ploquin et al, 2013;Savage & Vellend, 2015). Similar patterns have emerged across studies of different global change effects on insect communities, thus pointing to a worrying loss of beta diversity in this taxonomic group (Gossner et al, 2023).…”

Eutrophication modifies the relationships between multiple facets of macroinvertebrate beta diversity and geographic distance in freshwater lakes

“…These findings did not support the third hypothesis and were inconsistent with a recent study conducted in the same region, which indicated that nutrient enrichment led to taxonomic and functional homogenization of macroinvertebrate assemblages in most eutrophic lakes . Although eutrophication increases the importance of environmental filtering and decreases the effects of random processes in structuring biotic communities, the increase (differentiation) or decrease (homogenization) in compositional dissimilarity depends on complex mechanisms (Rolls et al, 2023), including initial ecological conditions, the magnitude and uniformity of disturbances and the sensitivity or tolerance of individual taxa (Chalcraft et al, 2008;Gutiérrez-Cánovas et al, 2013;Hawkins et al, 2015). In our study, despite the higher levels of nutrient concentrations, the algal-dominated (i.e., most eutrophic) lakes showed broader ranges of eutrophication-related water quality (i.e., transparency, TN, TP and Chl a and COD Mn ) than the macrophyte-dominated (or least eutrophic) lakes (Table S6)…”

Climate change impacts dryland multifunctionality: A cascade of precipitation variability to species replacement in multitrophic microbiota

“…G. Hu et al, 2021;Soliveres et al, 2016). It would hamper our mechanistic understanding of processes underlying the observed patterns of spatial variation in soil communities and functions along the gradient of climatic transects (A. S. Mori, Isbell, & Seidl, 2018;Rolls et al, 2023).…”

“…Despite this, the majority of biodiversity-ecosystem function relationship (BEF) studies were emerging from the perspective of single α -diversity and its linkage with local functional levels (Manuel Delgado-Baquerizo et al, 2016; W. G. Hu et al, 2021; Soliveres et al, 2016). It would hamper our mechanistic understanding of processes underlying the observed patterns of spatial variation in soil communities and functions along the gradient of climatic transects (A. S. Mori, Isbell, & Seidl, 2018; Rolls et al, 2023).…”