Love thy neighbour or opposites attract? Patterns of spatial segregation and association among crested penguin populations during winter

Abstract

AimCompetition for food among populations of closely related species and conspecifics that occur in both sympatry and parapatry can be reduced by interspecific and intraspecific spatial segregation. According to predictions of niche partitioning, segregation is expected to occur at habitat boundaries among congeners and within habitats among conspecifics, while negative relationships in the density of species or populations will occur in areas of overlap. We tested these predictions by modelling the winter distributions of two crested penguin species from three colonies in the south-western Atlantic.LocationPenguins were tracked from two large colonies on the Falkland Islands and one in South Georgia, from where they dispersed through the South Atlantic, Southern Ocean and south-eastern Pacific.MethodsForty macaroni penguins (Eudyptes chrysolophus) from South Georgia and 82 southern rockhopper penguins (Eudyptes chrysocome chrysocome) from two colonies in the Falkland Islands were equipped with global location sensors which log time and light, allowing positions to be estimated twice-daily, from April to August in 2011. Positions were gridded and converted into maps of penguin density. Metrics of overlap were calculated and density was related to remote-sensed oceanographic variables and competitor density using generalized additive models.ResultsMacaroni penguins from western South Georgia and southern rockhopper penguins from Steeple Jason Island, Falkland Islands, were spatially segregated by differences in their habitat preferences thus supporting our first prediction regarding interspecific segregation. However, southern rockhopper penguins from Beauchêne Island showed a marked spatial overlap with macaroni penguins as the two had similar habitat preferences and strong mutual associations when controlling for habitat. Contrary to our predictions relating to intraspecific segregation, southern rockhopper penguins from Beauchêne Island and Steeple Jason Island were segregated by differences in habitat selection.Main conclusionsMorphological differentiation probably allows macaroni penguins from South Georgia and southern rockhopper penguins from Beauchêne Island to coexist in areas of spatial overlap, whereas segregation of the two Falkland rockhopper penguin populations may have arisen from two distinct lineages retaining cultural fidelity to ancestral wintering areas.

Spatial and isotopic niche partitioning during winter in chinstrap and Adélie penguins from the South Shetland Islands

“…It is unknown if this westward movement pattern has developed since earlier tracking studies were conducted or whether previous tracking studies from the South Shetland Islands did not reveal this behavior because sample sizes were small (Wilson et al 1998). Of note, Ratcliffe et al (2014) reported that the macaroni (Eudyptes chrysolophus) and rockhopper (E. chrysocome) penguins tracked from South Georgia and the Falkland Islands exhibited high rates of occupancy in the Scotia Sea during winter. The westward movement of chinstrap penguins from the Peninsula region may, therefore, be a behavioral response to avoid high densities of these Eudyptes penguins in the central Scotia Sea.…”

“…We predict that spatial segregation of foraging areas will occur between species based on previously observations of differences in foraging areas evident during the breeding period (Wilson 2010) and winter observations that indicate Adélie penguins are more commonly observed in marginal ice zones while chinstrap penguins occupy open waters north of the ice edge (Ainley et al 1994). Because neighboring populations of con-specifics likely occupy the same ecological niche, we predict that chinstrap penguins from different colonies will exhibit relatively higher overlap in winter foraging areas and isotopic niche space, as intraspecific segregation would be expected to occur within a shared habitat rather than occupation of distinct habitats (Thiebot et al 2011, Thiebot et al 2012, but see Ratcliffe et al 2014). (Table 1) and fitted with Lotek Nano-Lat 2900-series archival geolocation tags (hereafter GLS; Lotek Wireless, St. Johns, Newfoundland, Canada) to monitor dispersal and habitat utilization.…”

“…In combination, direct tracking and SIA provide a robust toolset to quantitatively track the movements and foraging niches of wide-ranging marine organisms, including seabirds, throughout much of their annual cycle (González-Solís et al 2007, Block et al 2011, Polito et al 2011a, Seminoff et al 2012. Interestingly, recent studies using the approaches above have noted clear patterns of spatial and temporal foraging niche segregation within and between sympatric seabird species during the winter months when they are away from breeding colonies (Thiebot et al 2011, Ratcliffe et al 2014. These results suggest that some seabird assemblages have evolved behavioral mechanisms that help to limit inter and intra-specific competitive overlap during the non-breeding period.…”

Individual-level Variation and Higher-level Interpretations of Space Use in Wide-ranging Species: An Albatross Case Study of Sampling Effects

“…Commonly in multi-colony tracking studies, the size of the areas used and the degree of at-sea spatial segregation among seabird colonies are delineated by a pooled KDE from a sample of tracked individuals from each group. The size of pooled KDE 50 or 95% contours are quantified and compared, and the degree of overlap between groups is calculated (e.g., Young et al, 2009;Frederiksen et al, 2012;Thiebot et al, 2012;McFarlane Tranquilla et al, 2013;Ratcliffe et al, 2014). However, without consideration of individual variation within an available dataset, these higher-level inferences can be inadvertently misleading.…”

“…from the same colony during breeding), and the practice has since become commonplace. Some recent examples include the use of pooled KDE to compare space use between different annual periods for a species and colony (e.g., Robertson et al, 2014), different species from the same colony (e.g., Linnebjerg et al, 2013), different colonies of the same species (e.g., Young et al, 2009;Thiebot et al, 2011), and different species and colonies (e.g., McFarlane Tranquilla et al, 2013Tranquilla et al, , 2015Ratcliffe et al, 2014). …”