Introduction

In recent years the number of colonisation/invasion events has dramatically increased, the arrival of an alien species can spell disaster if they become established and begin to spread. Understanding the factors that facilitate or contain the establishment of populations in novel environments is crucial for conservation biology.

Objectives:

We sought to answer the following questions: 1) Does the timing of colonisation relative to stochastic events, such as climatic perturbations, impact the probability of successful establishment? 2) To what extent does community context (e.g., the presence of competitors) change the probability of establishment? 3) How do sources of intra-population variance, such as sex differences, affect success at an individual level during the process of establishment?

Methods:

We introduced slender anole lizards (Anolis apletophallus) to eight small islands in the Panama Canal and tracked them over multiple generations to investigate the factors that mediate establishment success. All islands were warmer than the mainland (ancestral) environment, and some had a native competitor. We transplanted half of these populations only four months before the onset of a severe regional drought and the other half two years (two generations) before the drought.

Results:

We found that successful establishment depended on both the intensity of interspecific competition and the timing of colonisation relative to the drought. The islands that were colonised shortly before the drought went functionally extinct by the second generation, and regardless of time before the drought, the populations on islands with interspecific competition declined continuously over the study period. Furthermore, the effect of the competitor interacted with sex, with males suffering, and females benefitting, from the presence of a native competitor.

Conclusions:

Our results reveal that community context and the timing of colonisation relative to climatic events can combine to determine establishment success and that these factors can generate opposite effects on males and females. Thus, accurate predictions of the likelihood of invasion will require an understanding of how features of the environment interact with the ecology of the alien species to drive population dynamics.