Spatial variation in demography and population growth rate: the importance of natal location
Jane M. Reid, School of Biological Sciences, Zoology Building, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK. E-mail: email@example.com
- 1Understanding the pattern and magnitude of spatial variation in demography and population growth rate (λ) is key to understanding the structure and dynamics of natural populations. However, such spatial variation is challenging to quantify. We use > 20 years of individual life-history data to quantify small- and large-scale spatial variation in demography and λ within a single population of red-billed choughs Pyrrhocorax pyrrhocorax on Islay, Scotland. Critically, we demonstrate a major importance of an individual's natal rather than current location in driving observed spatial variation.
- 2Breeding success (the number of offspring fledged per breeding attempt) varied among individual chough nest sites but did not vary on a larger spatial scale across Islay.
- 3The proportion of fledglings observed to survive to recruiting age varied markedly among individual nest sites and also varied more widely across Islay. Spatial capture–mark–recapture models defined two discrete geographical regions where fledgling survival differed significantly: choughs fledged in region ‘BGE’ were more likely to survive than choughs fledged in region ‘CNSW’ as both subadults and adults.
- 4The asymptotic λ attributable to breeding attempts in region BGE exceeded unity, and exceeded that attributable to breeding attempts in region CNSW. Relatively productive and unproductive regions therefore exist within this population.
- 5Spatial variation in adult survival was better explained by an individual's natal region than the region where that individual settled to breed. Spatial variation in λ would consequently have remained undetected had survival been measured across resident breeders rather than across individuals fledged in each region. Furthermore, breeding success was a weak predictor of a nest site's estimated productivity of recruits.
- 6We therefore describe marked spatial variation in demography and λ within a single population of a territorial vertebrate, mediated partly by long-term links between an individual's natal location and its subsequent life-history. Life-long monitoring of individuals of known origin may therefore be necessary to identify accurately subpopulations of intrinsically high and low λ.