Metapopulations, the inflationary effect, and consequences for public health

Abstract

The metapopulation perspective is an important conceptual framework in ecology and evolutionary ecology. Metapopulations are spatially distributed populations linked by dispersal. Both metapopulation models and their community and ecosystem level analogues, metacommunity and meta-ecosystem models, tend to be more stable regionally than locally and display enhanced abundance because of the interplay of spatiotemporal heterogeneity and dispersal (an effect that has been called the “inflationary effect”). We highlight the essential role of spatiotemporal heterogeneity in metapopulation biology, sketch empirical demonstrations of the inflationary effect, and provide a mechanistic interpretation of how the inflationary effect arises and impacts population growth and abundance. We illustrate the effect with examples from the spread of infectious disease. Namely, failure to recognize the full possible effects of spatiotemporal heterogeneity likely enhanced the spread of COVID-19, a failure based on lack of understanding of emergent population processes at large scales which may hamper control and eradication of other infectious diseases. We finish by noting how the effects of spatiotemporal heterogeneity have implicitly played roles in the history of ecology, ranging across subdisciplines as diverse as natural enemy-victim dynamics, species coexistence, and conservation biology. Seriously confronting the complexity of spatiotemporal heterogeneity could push many of these subdisciplines forward.

Partitioning the Impacts of Spatial-Temporal Variation in Demography and Dispersal on Metapopulation Growth Rates

“…Spatial-temporal variation, here, corresponds to the residual variation in fitness beyond spatial variation and temporal variation. This definition of spatial-variation coincides with recent work by Johnson and Hastings [2023] and Kortessis et al [2023]. Spatial-temporal variation always corresponds to spatial asynchrony in fitness i.e.…”

“…This type of decomposition of the demography is similar to decompositions used by Johnson and Hastings [2023] and Kortessis et al [2023].…”

“…For spatially structured populations, serially uncorrelated temporal variation in demographic rates still reduce population growth rates [Tuljapurkar, 1990, Boyce et al, 2006. However, if this temporal variation isn't perfectly spatially synchronized, dispersal can reduce its negative impact on population growth [Kuno, 1981, Metz et al, 1983, Wiener and Tuljapurkar, 1994, Jansen and Yoshimura, 1998, Evans et al, 2013, Jaggi et al, 2023, Kortessis et al, 2023. This reduction stems from dispersal marginalizing the amount of temporal variation experienced by the average individuals and, thereby, acting as a bet-hedging strategy.…”

“…Current theory, however, focuses only on part of this complexity. It either focuses only on demographic variation [Wiener and Tuljapurkar, 1994, Roy et al, 2005, Roy and Holt, 2009, Schreiber, 2010, Evans et al, 2013, Jaggi et al, 2023, Kortessis et al, 2023, or specific forms of dispersal variation [Schmidt, 2004, Williams and Hastings, 2013, Snyder et al, 2014. To place these complexities into a single integrative framework, I analyze a class of stochastic, matrix models with any number of patches and accounting for many forms of spatial-temporal variation in demography and dispersal.…”

Increasing environmental fluctuations can dampen variability of endogenously cycling populations

“…Thus, assuming fixed growth under average conditions, increasing environmental variability lowers long-term population growth [11], and the same nonlinear averaging effects apply at the level of demographic rates (see Real and Ellner [12] for a graphical application of this idea). This effect has been demonstrated empirically in the growth rate of experimental populations of green algae ( Tetraselmis tetrahele ) [13], in herbivore feeding rates [14], and in predator feeding rates [15] (although, in some cases, environmental variability can elevate average population growth, especially when the environment has some predictability [16] or populations are spatially distributed [17, 18]).…”