Oh deer! Population genomics reveals high connectivity of invasive deer among islands
Invasive species are major threats to global biodiversity, especially on islands. Using Sitka black-tailed deer in Haida Gwaii, Canada, we demonstrate how population genomic data can inform management decisions that target ecological restoration.
Ecologists and evolutionary biologists have long been fascinated by life on islands. While Darwin’s voyage to the Galapagos and beyond remains iconic for helping inspire the theory of evolution by natural selection, the work within Origin of Species also represents the important role that islands have had in shaping the distribution of life on our planet. Islands are often conveyed as wondrous places filled with unique biodiversity and culture; certainly, islands have much to offer in these regards, but unfortunately this means they also have much to lose.
Although islands are home to disproportionally high levels of species richness, they also face elevated levels of species extinctions, largely driven by the introductions of non-native species. One such example is Sitka black-tailed deer (Odocoileus hemionus sitkensis) in Haida Gwaii, an archipelago off the western coast of Canada. Haida Gwaii has often been referred to as the ‘Canadian Galapagos’, due to its outstanding biodiversity and Indigenous culture, as the Haida Nation have long been stewards of the islands. Since the introduction of deer during western colonization in the late 1800s, the natural balance of life on Haida Gwaii has been disrupted, jeopardizing many of these relationships, as several of the deer’s favorite foods are also culturally important species (Fig. 1-3).
Islands are often characterized by their inherent isolation, which may lead you to believe that deer would face a tough time dispersing from island to island. In Haida Gwaii, however, it seems deer have aptly demonstrated the proverb “where there’s a will, there’s a way”, because they currently reside on dozens of islands. Management initiatives aiming to remove deer from islands of high ecological and cultural value have therefore been challenged by the deer’s resilience, and many questions have been raised from incomplete eradications. Most importantly, are there islands that could remain deer-free after successful eradications?
We sought to answer this question, among others, in our recently published study using population genomic data from Sitka black-tailed deer harvested across Haida Gwaii, with an emphasis on deer connectivity within Gwaii Haanas National Park Reserve, National Marine Conservation Area, and Haida Heritage Site. Our findings confirmed previous anecdotal observations of deer movement among islands. In Juan Perez Sound especially, we identified several pairs of first and second order relatives harvested from different islands using a pairwise kinship analysis. In one example, a deer from Faraday was found to be the brother, father, or son of a deer from the Bischofs. Collectively, these inter-island relationships suggest plenty of deer movement among islands in Juan Perez Sound (Fig. 4).
At a larger scale, our study further demonstrates the utility of population genomics for informing invasive species management on islands. By estimating population connectivity as part of management operations, managers are better equipped to efficiently allocate resources to meet conservation and restoration goals. With the status of many unique island species becoming increasingly imperilled, their persistence may very well depend upon our ability to make evidence-based decisions towards the removal of island invaders, protecting our most rich and wonderful systems for future generations.
If you would like to learn more, please feel free to visit our open access paper in Communications Biology: https://doi.org/10.1038/s42003-022-03159-5