Associate Professor University of Colorado Denver Denver, Colorado, United States
Abstract: Increasingly extreme and variable environments can lead to population declines and range shifts. Such population fluctuations and movement can lead to the need to manage reintroductions or invasions, both of which require successful establishment of small populations. Population recovery or establishment depends on the response to environmental variation and the comparative impact of environmental and demographic stochasticity on population growth. Life history traits describe a species’ risk mitigating strategies and can predict long-term demographic performance. However, predicting the short-term fate of small populations is necessary to prevent invasions or ensure the success of reintroductions. Using 1,606 empirical matrix population models form the COMPADRE plants database representing multiple years or populations of 317 plant species, we simulated asymptotic and stochastic (environmental and demographic) conditions and stable stage and single stage (seed or vegetative) structure to estimate the risk of near-term extinction (10 years). To identify correlates of persistence, we classified empirical matrix population models by pace of life and examined the effect of reproductive strategy, finite population size, founding population stage, stable and unstable structure, and stochasticity on short-term persistence.
A species’ pace and mode of reproduction balance and reduce risk over time and across individuals. Environmental stochasticity increased extinction risk while demographic stochasticity reduced risk. Repeated and even reproductive effort (iteroparity), the combination of demographic and environmental stochasticity, and an increasing population size reduced the probability of extinction. While founding population size had the largest effect (0.16 reduction for slow, 0.35 reduction for fast species), founding population size, iteroparity and stochasticity reduced risk more for slow than fast life histories. Iteroparity reduced risk 0.39 times for slow life histories but only 0.89 times for fast species, demographic and environmental stochasticity decreased risk 0.28 times for slow and 0.63 times for fast species, and iteroparity with environment and demographic stochasticity decreased the probability of extinction 0.18 times for slow and 0.42 times for fast life histories. A larger founding stage improved persistence regardless of life history but is more impactful for iteroparous than semelparous life histories. Semelparous life histories with high fecundity are at greater risk of becoming invasive. These findings are useful to move beyond a species-by-species evaluation of invasiveness or one-size fits all guidelines for restoration, reintroductions, and harvest rates.
