Metapopulation regulation acts at multiple spatial scales: Insights from a century of seabird colony census data

Abstract

Density-dependent feedback is recognized as important regulatory mechanisms of population size. Considering the spatial scales over which such feedback operates has advanced our theoretical understanding of metapopulation dynamics. Yet, metapopulation models are rarely fit to time-series data and tend to omit details of the natural history and behavior of long-lived, highly mobile species such as colonial mammals and birds. Seabird metapopulations consist of breeding colonies that are connected across large spatial scales, within a heterogeneous marine environment that is increasingly affected by anthropogenic disturbance. Currently, we know little about the strength and spatial scale of density-dependent regulation and connectivity between colonies. Thus, many important seabird conservation and management decisions rely on outdated assumptions of closed populations that lack density-dependent regulation. We investigated metapopulation dynamics and connectivity in an exemplar seabird species, the Northern gannet (Morus bassanus), using more than a century of census data of breeding colonies distributed across the Northeast Atlantic. We developed and fitted these data to a novel hierarchical Bayesian state-space model, to compare increasingly complex scenarios of metapopulation regulation through lagged, local, regional, and global density dependence, as well as different mechanisms for immigration. Models with conspecific attraction fit the data better than the equipartitioning of immigrants. Considering local and regional density dependence jointly improved model fit slightly, but importantly, future colony size projections based on different mechanistic regulatory scenarios varied widely: a model with local and regional dynamics estimated a lower metapopulation capacity (645,655 Apparently Occupied Site [AOS]) and consequently higher present saturation (63%) than a model with local density † Passed away 1 January 2022.

High pathogenicity avian influenza (H5N1) in Northern Gannets (Morus bassanus): Global spread, clinical signs and demographic consequences

“…2022, Jeglinski et al . 2023). During the breeding season, Gannets are medium‐range foragers, capable of travelling more than 1000 km to find food (Hamer et al .…”

High pathogenicity avian influenza (H5N1) in Northern Gannets: Global spread, clinical signs, and demographic consequences

“…Around one quarter of nests with an egg on 15 th June still had a chick in late August, which is much lower than the mean UK gannet breeding success during 1961-2018 (mean ± standard deviation) 0.72 ± 0.12 (Jeglinski et al 2023). There are methodological differences in approach, but the comparison provides a further indication of the severe impact of the virus.…”

“…Ophthalmology exams or histopathology examinations are also required to determine what is causing the black colouration. It is also desirable to better understand the circulation of LPAIVs and prior exposure to antigenically related HPAIV sub-types in seabird populations to better understand potential cross-protective immunity, as well as the potential for compensatory recruitment to offset mortality (Votier et al 2008, Jeglinski et al 2023.…”

“…Gannets breed in 53 colonies of various sizes (<10 to >60,000 breeding pairs and non-breeding immatures) on sea cliffs, stacks, and islands across both sides of the North Atlantic from Russia to north-eastern North America (d 'Entremont et al 2022a, Jeglinski et al 2023. During the breeding season, gannets are medium-range foragers capable of travelling more than 1000 km to find food (Hamer et al 2007).…”

“…We quantify how the 2022 HPAIV outbreak influenced adult survival and breeding success and present a non-invasive method that has the potential to determine exposure status based on iris colour. We collated and mapped data on the timing of unusually high gannet mortalities (the earliest observations notable to fieldworkers familiar with their sites) at existing colonies across the global metapopulation as defined by Jeglinski et al 2023. Colonies in Norway, Iceland and some Irish colonies were not monitored directly, but instead we gathered information on dead gannet sightings reported to the Norwegian Species Observation System (www.artsobservasjoner.no),)the Icelandic Food and Veterinary Authority and to the Department of Agriculture, Food and the Marine's (DAFM) Avian Check App (https://aviancheck.apps.services.agriculture.gov.ie/), and we associated these observations with the nearest gannet breeding colony.…”