Effect of a Magellanic penguin colony on a small mammal assemblage reveals potential of seabirds to modulate terrestrial communities: Ecological and methodological approaches

Abstract

Small mammals are considered bioindicators of environmental quality and show rapid population responses to seasonal environmental variations. These variations are accentuated at high latitudes, and, in coastal regions of the southern hemisphere, they can be further enhanced by the presence of penguin breeding colonies, which provide additional resources to breeding sites. Small mammals' studies generally use physical capture (PC) that may harm animal welfare. The search for less invasive methods should be encouraged. Based on the prediction that penguins’ colonies would intensify the effects of seasonality on small mammal, we examined the influence of seasonality and Magellanic penguin (Spheniscus magellanicus) presence on these animals, as a model of how seabird colonies modify terrestrial communities. Using data from PC, we compare the seasonal variation in the abundance and diversity of small mammals between the colony and its surroundings. We also use camera trap data (CT) to define spatial variations in the abundance and activity of the studied assemblage throughout the year, and to indicate applications of this method in the study of small mammal ecology. Compared to the surroundings, the colony supports a greater abundance of small mammals throughout the year (confirmed by PC and CT data), and greater species diversity when penguins are present (PC data). In general, the colony favoring species different from those most abundant in the surrounding area, which increases regional biodiversity (PC data). Activity intensity of small mammals increases earlier in the surrounding than in the colony (CT). As bioindicators, the observed responses of the small mammal community demonstrated that the colony could guarantee more resources and that last longer. This can be assumed because the abundance and diversity of species are positively related to resources, while the delay in the increase in foraging compared to the surroundings indicates that resources are depleted faster in this last environment. Therefore, seabirds’ colonies could function as key environments and these birds could represent ecosystem engineers, since they modulate terrestrial communities. Our data also demonstrated that CT represented an efficient complementary method, although it can be used separately in the study of small mammals at the assemblage level.