Beta Diversity of Antarctic and Sub-Antarctic Benthic Communities Reveals a Major Role of Stochastic Assembly Processes

Abstract

Community assembly is the result of both, deterministic and stochastic processes. The former encompasses niche-based local-scale mechanisms such as environmental filtering and biotic interactions; the latter includes ecological drift, probabilistic colonisation, and random extinctions. Using standardised sampling protocols, we show that the spatial variation in species composition (beta diversity) of shallow subtidal macrobenthic communities of sub-Antarctic (Strait of Magellan and Yendegaia Fjord [Beagle Channel]) and Antarctic (Fildes Bay [King George Island, West Antarctic Peninsula]) localities reflects a high contribution of stochastic processes to community assembly. Null model analyses indicated that random sampling from species pools of different sizes drove the observed among-locality differences in incidence- and abundance-based beta diversity. We analysed a normalised stochasticity ratio (NST), which delimits between more deterministic (<50%) and more stochastic (>50%) assembly. NST was notably larger than 50%, with mean values of 69.5% (95% CI = 69.2–69.8%), 62.5% (62.1–62.9%), and 72.8% (72.5–73.2%) in Strait of Magellan, Yendegaia Fjord, and Fildes Bay, respectively. Accordingly, environmental factors, such as depth, seawater temperature, salinity, and underwater light penetration, accounted for a small fraction of the spatial variation in community composition across the three localities. In this region, therefore, stochastic processes could have stronger effects on community assembly than deterministic niche-based factors. As anthropogenic biotic homogenisation continues apace, our study can give useful insights into the major ecological processes in Southern Ocean’ coastal marine communities.

Tropical invertebrate community assembly processes are robust to a gradient of land use intensity

“…Numerous studies have investigated the relative importance of stochasticity and determinism in different environments (e.g. Ellwood et al 2009, Caruso et al 2012, Shipley et al 2012, Ortega-Martínez et al 2020, Valdivia et al 2021). However, an understanding of the effects of land use change on the relative importance of stochastic and deterministic community assembly processes is largely absent, despite its potential importance.…”

Resilience of tropical invertebrate community assembly processes to a gradient of land use intensity

“…Determinism and stochasticity are opposite ends of a continuum, with real‐world communities existing somewhere between these extremes (Gravel et al 2006, Kitching 2013). Previous studies have investigated the balance between stochasticity and determinism in different environments (Ellwood et al 2009, Caruso et al 2012, Shipley et al 2012, Ortega‐Martínez et al 2020, Valdivia et al 2021), but few have addressed the impact of land use change on this balance, despite the potential importance of this. It is often suggested that community assembly processes exhibit hysteresis (Beisner et al 2003), implying that restoring an ecological community in a modified habitat could rely on different assembly processes than those that exist in primary habitats (Andersen et al 2009, Suding and Hobbs 2009).…”