Adelie and Gentoo penguins are two closely related Pygoscelis penguins with overlapping breeding ranges on the Western Antarctic Peninsula. The foraging strategies of these two species vary widely across their breeding ranges and little is known about their foraging niches at Palmer Station, Anvers Island.
Is intraspecific competition driving population trends at Palmer Station?
It remains unclear whether intraspecific competition is occurring between Adelie and Gentoo penguins at Palmer station. This is a particularly important question to answer in this region, where climate-induced warming and sea ice loss has significantly altered habitat, marine food web dynamics, and the community structure of Pygoscelis penguins. In this area, populations of Adelie penguins have been declining over the last four decades while numbers of Gentoo penguins have been increasing. In this context, it is important to gain a better understanding of how these two species partition their shared prey resource. This study will contribute to knowledge to current theories explaining the contrasting population trends of Adelie and Gentoo penguins, and help to determine the extent that intraspecific competition is driving these trends.
As central place foragers, Adelie and Gentoo penguins are constrained by the spatial and temporal distribution of their prey, which in this region is principally Antarctic krill. In order to co-exist as sympatric predators, these species must partition their shared prey resource by foraging in different locations, at different depths and/or at different times of the day. The objective of my project is to investigate foraging ranges of Adelie and Gentoo penguins and quantify the degree of overlap between them, if any.
My hypothesis is that the foraging ranges of these two species will overlap. Due to the constraint imposed upon them as central place foragers, seabirds rely on foraging in locations with predictable prey patches. The islands that each of these species breed on are relatively close together (within the distance that each species is known to swim on a single foraging trip) and it is likely that both species are cued into aggregations of prey in similar areas.
I will be utilizing satellite telemetry to examine the foraging ranges of these species and to test this hypothesis. Fieldwork was conducted through a Long Term Ecological Research project based out of Palmer Station, Anvers Island. We tracked Adelie and Gentoo penguins between 5 Jan-2 Feb 2015 using platform terminal transmitters (PTTs). A total of 15 Adelie and 7 Gentoo penguins carried these tags for roughly 3 days each during this study period. Location data were downloaded from Argos. My first step in this project will be to pre-process these data by filtering out erroneous data points, and I am considering using the R package argosfilter to do this. Following this step, I intend to import these data points into ArcGIS and utilize the Spatial Analyst extension tool to create kernel density estimates of foraging ranges. I am interested in quantifying the total foraging area utilized by each species as well as core foraging areas. Previous studies have done this by using 50% and 95% kernel density estimates and calculating the area within each of those contour lines. This will allow me to visually and quantitatively describe the space that each of these species is utilizing to forage. Following these steps, I plan to calculate the proportion of overlap between each of these species ranges. In addition to learning how to conduct the analyses above, I am interested in exploring ArcView’s Animal Movement extension, and determining whether it might be useful for this project.
I anticipate that I will produce a series of maps that illustrate the foraging ranges of these two species over this study period. In addition to this I will calculate the total area (km²) of these ranges, and the percentage of overlap between these ranges. I expect that these results will provide us with a better understanding of whether intraspecific competition is a mechanism behind the contrasting population trends of Adelie and Gentoo penguins in the Palmer region. Up until this point, it has been difficult to discern the relative influence of sea ice loss on penguin habitat versus its effects on marine primary productivity and food web dynamics. The value of using these apex predators as indicator species will increase if we are able to determine the proximal causes behind their responses to environmental variability. This study will leave us better informed to infer population-level responses to increased competition in the Palmer region.
Regarding my previous experience with the tools we will be using in class- my knowledge of ArcGIS and R is basic, and I do not have any experience with Modelbuilder or Python.
