Negative density-dependence buffers against mismatch-induced population decline in the Sinai baton blue butterfly.

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Phenological mismatches caused by climate change pose a major threat to global biodiversity, yet relatively few studies have reported population declines resulting from mismatch. It has been hypothesised that density effects may underlie this lack of observed responses by buffering against mismatch-induced population decline. We developed an individual-based model of the critically endangered Sinai baton blue butterfly (Pseudophilotes sinaicus) and its hostplant Sinai thyme (Thymus decussatus), parameterised using real field data, to test this hypothesis. Our model showed that the baton blue experiences demographic consequences under only 5 days of phenological mismatch, but that this threshold was increased to 14days with the inclusion of density-dependent juvenile mortality. The inclusion of density effects also led to the replication of population cycles observed in nature, supporting the ability of our model to accurately represent the baton blue's ecology. These results add to a growing body of literature suggesting that density effects may underlie the observed lack of demographic responses to mismatch in wild populations. However, these buffers may be short-lived in extreme mismatch scenarios, providing a false sense of security against a looming threat of population collapse.