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Small Populations, Large Conservation Challenges: The Surprising Power of Sporadic Events
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by Madeline Eppley, edited by Swapna Subramanian and Julia Harenčár
“Sporadic Events Have a Greater Influence on the Dynamics of Small, Isolated Populations Than Density Dependence and Environmental Conditions”
Roxanne Turgeon, Fanie Pelletier, Steeve D. Côté, Marco Festa-Bianchet, and Sandra Hamel: Read the article
Turgeon et al. evaluated the relative influence of density-dependence, environmental conditions, and sporadic events (disease outbreaks and specialist predators) on annual population growth and demographic rates using long-term (30-47 years) data of three mountain ungulate populations
What if the factors most influencing the size of small populations aren’t the usual suspects like resource competition or environmental factors but rather random and unpredictable events? Roxanne Turgeon of Université Laval in Canada, et al. found that sporadic events, such as years of unusually high predation or disease outbreaks, can have a dramatic impact on small population dynamics. These impacts surpass the effects of density-dependence or environmental factors that ecological theory has long emphasized.
Turgeon et al. leveraged a long-term dataset dating back nearly 50 years to address this debate in three small and isolated bighorn sheep and mountain goat populations. By characterizing years with sporadic events such as cougar predation or pneumonia outbreaks, they found that these sporadic events have the strongest relative influence on annual changes in population size. This study upends assumptions by highlighting that population dynamics can be driven more by random events than consistent environmental factors.
These random events resulted in detrimental effects on the small sheep and goat populations. In years of severe predation, Turgeon et al. found a substantial decrease in juvenile survival rates as mothers had to redirect resources to survival over maternal care. In years with pneumonia outbreaks – caused by exposure to domestic livestock – survival rates for both juveniles and adults fell.
One of the most compelling takeaways from this study is the lack of synchrony among the populations despite similarity in environmental conditions. This finding suggests that since predation and disease are highly localized and sporadic, they cause inconsistencies between sheep and goat populations. This unpredictability suggests that small, isolated populations are highly vulnerable to local events, which challenges current conservation approaches. In an era of rapid, severe environmental change and novel disease outbreaks, Turgeon et al.’s research has profound implications for conservation and management strategies. Their results imply that management must consider unpredictable events as large factors in the population dynamics of small and isolated populations and take action to protect populations where possible.
Ultimately, while density-dependent factors and environmental conditions remain important, Turgeon et al. demonstrate that we cannot underestimate the influence of sporadic events. If we are to have a chance at protecting small populations during this time of rapid environmental change, we must account for random and unprecedented events.
Madeline Eppley is a PhD candidate at Northeastern University’s Marine Science Center in the Lotterhos Lab studying wild eastern oysters. They are interested in how populations of marine organisms genetically adapt over time, especially to rapid environmental change and the biotic landscape. Outside of science, Madeline enjoys watching women’s sports, weightlifting, and spending time near the ocean. www.madeline-eppley.com | @madeline-eppley.bsky.social
