Intrinsic ecological dynamics drive biodiversity turnover in model metacommunities

Abstract

1 Turnover of species composition through time is frequently observed in nature. 2 Often explained by changes in abiotic conditions or regional species pools, 3 compositional turnover is employed as an indicator of external stress in nat-4 ural ecosystems. Theoretically, the possibility of turnover driven by intrinsic 5 ecological dynamics-species interactions, dispersal-is also known, but what 6 role such autonomous turnover plays in nature remains unclear. Expanding 7 the boundaries of metacommunity modelling, we show that in large meta-8 communities immigration pressure from neighbouring locales robustly drives 9 continuous turnover in local composition-without environmental change or 10 regional invasions. That ecological communities may turn over autonomously 11 challenges assumptions implicit in assessment and management tools, and sug-12 gests that natural compositional change should be incorporated in ecological 13 status assessments based on ancestral baselines. 14 Main Text: 15 Change in species composition through time, called community turnover, is observed in most 16 ecosystems (1-3). Potential drivers include changes in the abiotic environment (4-6), random 17 population fluctuations due to demographic stochasticity (7), and autonomous population dy-18 namics driven by species interactions and dispersal (8, 9). While there exist well-developed 19 bodies of theory describing community turnover due to environmental change (10, 11) and 20 demographic stochasticity (12), our understanding of autonomous compositional change is un-21 derdeveloped. In particular, it remains unclear to what extent observed spatio-temporal patterns 22 in biodiversity may be due to autonomous ecological dynamics. 23If it were known that intrinsic ecological dynamics alone cannot account for observed com-24 2 positional turnover, then abiotic environmental change would be the most plausible explanation 25 (turnover by demographic stochasticity alone is predicted to be orders of magnitude slower than 26 observed (1)). In the current phase of rapid anthropogenic environmental change, any altera-27 tion in the composition of an ecological community should then be interpreted as a potential 28 indicator of stress (13)(14)(15) and the degree of compositional change compared to past baselines 29 a valid measure of anthropogenic impact. 30If, on the other hand, temporal community turnover is a natural phenomenon that can arise 31 independently of changes in the abiotic environment, then observed shifts in the composition 32 of ecological communities would not necessarily imply the presence of external pressures. 33Intrinsic dynamics may even permit ecosystems to adapt and absorb environmental change 34 without impacting ecosystem functioning. Assessments, projections and mitigation strategies 35 would then need to account for such autonomous compositional turnover. 36 So, can communities of many interacting species turn over autonomously? If so, what is 37 the driving mechanism? And does the resulting turnover reproduce patt...

Community composition exceeds area as a predictor of long-term conservation value

“…1A) was modelled by randomly sampling Cartesian coordinates from a uniform distribution in the range where N is the number of sites. As in previous studies (O’Sullivan et al, 2019, 2021a), we linked nearby sites using a Gabriel graph (Gabriel and Sokal, 1969).…”

“…Metacommunity dynamics were modelled using a spatial extension to the classic Lotka-Volterra community model (O’Sullivan et al, 2019, 2021a) where B ix represents the biomass of the i th species in the x th site. R ix are the intrinsic growth rates, which vary across the landscape.…”

“…Here, we explore the long-term outcomes of habitat destruction using a spatially explicit simulation model called the Lotka-Volterra Metacommunity Model (LVMCM), which has been shown to reproduce a large variety of well-documented patterns of spatio-temporal macroecology (O’Sullivan et al, 2019, 2021a). We model habitat conversion as the complete removal of sites from a metacommunity, and find that indeed the biotic impacts following site removal can be complex.…”

Intrinsic ecological dynamics drive biodiversity turnover in model metacommunities

“…The software used to generate these data is available at https://github.com/jacobosullivan/ LVMCM_src 86 .…”