Intra- and interspecific interactions among king penguins

Our hypothesis is that there will be more social behaviours in intraspecific interactions in comparison to interspecific interactions in king penguins. Our study will be focusing on the theory of economic defensibility to support our hypothesis. This theory predicts that individuals will only defend a territory when the benefits outweigh the costs, such as energy and risk of injury (Rubenstein & Alcock, 2019). Since defending a territory and competing with one another costs energy, we expect less social behaviours to be observed between king penguins and other species since they would be fighting for different resources and the trade-off would result in minimal benefit for either species. In intraspecific interactions, however, we are expecting to see more social behaviours since the king penguins share the same resources.

If our hypothesis is supported and there are more social behaviors observed in intraspecific interactions in king penguins then this study can be used to support king penguins “natural” behaviours outside of zoo enclosures, in nature. We believe different species of penguins will occupy different areas within the zoo enclosure. When observing interspecific interactions we expect to see minimal social behaviours due to their different realized niches. We expect penguins within their species to have more social interactions because of their shared realized niche and competition.

To explain our predictions, we found research on various other penguin species and their interspecific and intraspecific interactions in nature. A study done by Ratcliff et al. (2018) on dietary divergence with intraspecific competition in gentoo penguins on Bird Island found that during chick-rearing periods resources became limited. This drove adult gentoo penguins to increase their foraging range (Ratcliffe et al., 2018). As a result, the adult gentoo penguins spent more time at sea trying to compensate for this increase in intraspecific competition by incorporating more mackerel icefish due to a decline in krill (Ratcliffe et al., 2018).

This suggests that the dietary niche of populations can be widened in response to intraspecific competition (Ratcliffe et al., 2018). This study also explores how interspecific interactions also might have contributed to the decline in krill. The Island gentoo penguins live on is also shared with macaroni penguins and Antarctic fur seals that also consume large amounts of krill (Ratcliffe et al., 2018). Gentoo penguins’ unique foraging niches allow them to avoid being greatly affected by interspecific competition (Ratcliffe et al., 2018).

Similarly, a study by Dann and Norman (2006) focused on intraspecific

competition for nesting and food during breeding among Little Penguins and its effects on population control. Little penguins have a very small foraging range and are more susceptible to food shortages during breeding times resulting in intraspecific competition (Dann & Norman, 2006). This can lead to Little Penguins becoming susceptible to density-dependant shortages during breeding seasons (Dann & Norman, 2006), meaning that the more individuals there are, the less available food and space. This may ultimately lead to a reduction in population size. For example, in the absence of food the cost of foraging is significantly higher than the benefits, and on large islands this may negatively affect the reproductivity of Little Penguins (Dann & Norman, 2006). Further, if the breeding site is too far the individual may not be able to successfully reach it due to predation risk and the overall energetic cost of walking (Dann & Norman, 2006).

A very similar study was also done several years before by Forero et al. (2002) in which the researchers focused on population density of Magellanic penguins with a stronger emphasis on food availability. This study yielded comparable results, as the colony size of the Magellanic penguins and the number of healthy offspring produced were found to be negatively correlated (Forero et al., 2002). What this means is that there is significant evidence that breeding success and population size are heavily influenced by foraging patterns, as well as intraspecific competition for nesting areas (Dann & Norman, 2006) and food depletion (Forero et al., 2002).

In terms of interspecific interactions a study was done between Adélie and chinstrap penguins, exploring the complications that can arise between two similar species when resource availability is limited during breeding seasons (Lynnes et al., 2002). Due to both penguin species in this study showing a sympatric diet and breeding zones one of the main questions the authors were discussing was how they coexist (Lynnes et al., 2002). They found Adélie penguins were more likely to expand their foraging ranges and feed farther away from the breeding colony in comparison to chinstrap penguins when there was less krill (Lynnes et al., 2002). The Adélie penguins had a lower reproductive success rate during this time, suggesting competitive exclusion (Lynnes et al., 2002). Although when krill was abundant the penguins’ foraging ranges overlapped but both species displayed above average reproductive success (Lynnes et al., 2002).

The researchers also explored the effects of sea-ice, when there was no sea-ice and plentiful resources both species of penguins have equal reproductive success suggesting food availability inshore and offshore is similar, but when there is sea-ice and less food availability the chinstrap species are at an advantage because of there food availability in inshore habitats (Lynnes et al., 2002). This means interspecific species interactions are costly once there are limited resources because competitive exclusion starts to take over. In this case the chinstrap species were able to maintain reproductive success because inshore habitats were able to readily provide appropriate resources while the sea-ice in offshore areas created a barrier for the Adélie penguins (Lynnes et al., 2002). This forced Adélie penguins to expand their foraging ranges but was essentially more energy expensive, resulting in lower overall reproductive success (Lynnes et al., 2002).

Another study looking at interspecific interactions, Pickett et al. (2018) found that gentoo penguins and Adelie penguins are ecologically similar organisms that share a limited resource of krill. Due to this, the two species partitioned the krill through horizontal segregation, and thus avoided interspecific competition (Pickett et al., 2018). This relates to the main theory of our experiment, that organisms will only compete for a resource when the benefits outweigh the costs (Rubenstein & Alcock, 2019). Here, the two penguin species partitioned the resources rather than compete, as the cost of competing would have been too high. Similarly, we believe that king penguins also avoid competition with other penguin species, especially since they may not need the exact same resources as other penguins.

The findings in these studies can potentially extend to other seabird species, such as king penguins, in order to further understand the complex relationships and interactions they have with interspecific and intraspecific species. The information provided about interspecific and intraspecific behaviours can be beneficial to conservation biologists and zookeepers because it may allow them to determine whether or not zoo king penguin social behaviours in these interactions align with their theoretical behaviours in nature.

Current literature in varying seabird species demonstrates the various ways in which intraspecific competition can negatively affect a penguin population in terms of reproductive success, food, available space, and size. The studies by Forero et al. (2002), Dann and Norman (2006), and more recently by Ratcliff et al. (2018) are strong examples of this and can be used to support our hypothesis about the intraspecific behavioural patterns king penguins may exhibit in nature. In those papers, the researchers discuss the ways in which a single penguin species may be competing amongst themselves for the resources they share, and how this can lead to a decline in those resources and ultimately the population of penguins.

On the other hand, the studies conducted by Pickett et al. (2018) and Lynnes et al. (2002) can be used to support our hypothesis in regards to interspecific competition, and the behaviours observed in these studies could potentially be observed between king penguins and other penguin species. Our study aims to examine these concepts more closely in order to see if the concept may be applied to king penguins, a species not covered in relevant literature. Further, our study will provide insight as to whether or not the behaviour of penguins in their natural habitat is observed in captivity as well, since our only access to penguins is a zoo.