Give chance a chance: from coexistence to coviability in biodiversity theory

Abstract

A large part of biodiversity theory is driven by the basic question of what allows species to coexist in spite of a confined number of niches. A substantial theoretical background to this question is provided by modern coexistence theory (MCT), which rests on mathematical approaches of invasion analysis to categorize underlying mechanisms into factors that reduce either niche overlap (stabilizing mechanisms) or the average fitness differences of species (equalizing mechanisms). While MCT has inspired biodiversity theory in the search for these underlying mechanisms, we feel that the strong focus on coexistence causes a bias toward the most abundant species and neglects the plethora of species that are less abundant and often show high local turnover. Given the more stochastic nature of their occurrence, we advocate a complementary cross‐level approach that links individuals, small populations, and communities and explicitly takes into account (1) a more complete inclusion of environmental and demographic stochasticity affecting small populations, (2) intraspecific trait variation and behavioral plasticity, and (3) local heterogeneities, interactions, and feedbacks. Focusing on mechanisms that drive the temporary coviability of species rather than infinite coexistence, we suggest a new approach that could be dubbed coviability analysis (CVA). From a modeling perspective, CVA builds on the merged approaches of individual‐based modeling and population viability analysis but extends them to the community level. From an empirical viewpoint, CVA calls for a stronger integration of spatiotemporal data on variability and noise, changing drivers, and interactions at the level of individuals. The resulting large volumes of data from multiple sources could be strongly supported by novel techniques tailored to the discovery of complex patterns in high‐dimensional data. By complementing MCT through a stronger focus on the coviability of less common species, this approach can help make modern biodiversity theory more comprehensive, predictive, and relevant for applications.

Mean growth rate when rare is not a reliable metric for persistence of species

“…We examine two measures of persistence: one is the chance of invasion from rarity, a standard metric used in MCT and many other theories (Grainger et al, 2019), and the other is the time to extinction of an already established population, another standard metric whose importance has been highlighted in recent studies (Adler & Drake, 2008;Carmel et al, 2017;Jeltsch et al, 2019). The chance of invasion is the probability of a rare population to reach a given density before going extinct.…”

Technical Comment on Pande et al. (2020): Why invasion analysis is important for understanding coexistence

“…Angert et al, 2009;Usinowicz et al, 2012;Letten et al, 2018;Hallett et al, 2019). Analysis of IGRs can be supplemented when necessary with other persistence metrics (Jeltsch et al, 2019); a challenge for future research will be to understand when and how the positive relationship between IGR 1 and T ext breaks down. In principle, any persistence metric, including T ext , can be partitioned into contributions from different mechanisms, as Simulation results for an asymmetric lottery model with lognormal temporal variation in per capita fecundity, logB j t ð Þ ∼ Normal μ j ,σ 2 ,μ 1 ¼ 0:45,μ 2 ¼ 0:5: (a) IGR 1 (the smaller of the two IGRs) with δ ¼ 0:5.…”

“…Angert et al ., 2009; Usinowicz et al ., 2012; Letten et al ., 2018; Hallett et al ., 2019). Analysis of IGRs can be supplemented when necessary with other persistence metrics (Jeltsch et al ., 2019); a challenge for future research will be to understand when and how the positive relationship between and breaks down.…”

Editorial: thematic series “Integrating movement ecology with biodiversity research”

“…Movement, however, is particularly important to consider for the majority of species, which have low abundances and are thus strongly affected by temporal and spatial heterogeneity and individual interactions. The recently proposed conceptual framework of "coviability" [12] therefore suggests a better integration of individual organism and their behavior into community theory and, hence, biodiversity research. Moreover, also for another key question of biodiversity research, how species composition will change due to range shifts and invasive species, a mechanistic understanding of movement, in particular dispersal, is critical [22].…”

“…Empirically, we need more studies that not only focus on the movement of individuals, but also how they interact, while moving, with their environment and with other individuals, including their own and other species. From a theoretical viewpoint, there is a lack of modelling approaches that integrate individual movement and its consequences with population and community dynamics [12].…”