Distribution Patterns Predict Individual Specialization in the Diet of Dolphin Gulls

Abstract

Many animals show some degree of individual specialization in foraging strategies and diet. This has profound ecological and evolutionary implications. For example, populations containing diverse individual foraging strategies will respond in different ways to changes in the environment, thus affecting the capacity of the populations to adapt to environmental changes and to diversify. However, patterns of individual specialization have been examined in few species. Likewise it is usually unknown whether specialization is maintained over time, because examining the temporal scale at which specialization occurs can prove difficult in the field. In the present study, we analyzed individual specialization in foraging in Dolphin Gulls Leucophaeus scoresbii, a scavenger endemic to the southernmost coasts of South America. We used GPS position logging and stable isotope analyses (SIA) to investigate individual specialization in feeding strategies and their persistence over time. The analysis of GPS data indicated two major foraging strategies in Dolphin Gulls from New I. (Falkland Is./Islas Malvinas). Tagged individuals repeatedly attended either a site with mussel beds or seabird and seal colonies during 5 to 7 days of tracking. Females foraging at mussel beds were heavier than those foraging at seabird colonies. Nitrogen isotope ratios (δ15N) of Dolphin Gull blood cells clustered in two groups, showing that individuals were consistent in their preferred foraging strategies over a period of at least several weeks. The results of the SIA as well as the foraging patterns recorded revealed a high degree of specialization for particular feeding sites and diets by individual Dolphin Gulls. Individual differences in foraging behavior were not related to sex. Specialization in Dolphin Gulls may be favored by the advantages of learning and memorizing optimal feeding locations and behaviors. Specialized individuals may reduce search and handling time and thus, optimize their energy gain and/or minimize time spent foraging.

Shifting individual habitat specialization of a successful predator living in anthropogenic landscapes

“…Individual specialization is known to be widespread across a diverse set of taxa (Bolnick et al 2003, Bell et al 2009, Ceia & Ramos 2015, including different seabird species and other marine predators (e.g. Vander Zanden et al 2010, Votier et al 2010, Masello et al 2013, Ceia & Ramos 2015, Tyson et al 2015, Towner et al 2016, Yurkowski et al 2016. In general, individual specialization may have a strong impact on ecological processes and population dynamics, and there is evidence that this mechanism may reduce intra-specific competition among individuals, increase individual foraging efficiency and improve breeding success (Pierotti & Annett 1991, Bolnick et al 2003, Woo et al 2008, Araújo et al 2011.…”

Intra- and inter-individual variation in the foraging ecology of a generalist subantarctic seabird, the gentoo penguin

“…These may provide gentoos greater resilience to buffer against changes in prey availability and fast changing environmental conditions, especially as their foraging range is usually limited (Lescroël & Bost 2005, Polito et al 2015. However, within this context, gentoos still exhibit individual specialisation, helping them reduce intra-specific competition and/or increasing their foraging efficiency (dit Durell 2000, Masello et al 2013). Dietary specialisations outside of a single breeding season were also highlighted, suggesting that gentoo penguins are type 'B' generalists.…”

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

“…When data on diet are not available, behavioural information (such as dive depths and the proportion of trips associated with fishing boats) or the use of areas where particular prey occur (proportion of time at each feeding site) have been used to assign individuals to different diet groups (e.g. Ropert-Coudert et al 2003, Montevecchi et al 2009, Masello et al 2013, Patrick et al 2015, Tyson et al 2015. The threshold used for separating specialists and generalists is often arbitrary.…”

“…Indeed, if individuals specialise on different resources or environments over different seasons, studying specialisation over the whole year, for example, might prevent the detection of individual specialisation (although this issue can be dealt with by including the correct fixed effects). In the case of seabirds, although several studies have revealed that dietary and behavioural specialisations are widespread, it is unclear for how long these specialisations are maintained (Masello et al 2013, Patrick et al 2014; but see Wakefield et al 2015). It is likely, however, that repeatability in foraging behaviour declines at longer temporal scales because of temporal changes in the availability and predictability of resources (Woo et al 2008, Bell et al 2009, Ceia et al 2014.…”

“…The extent of niche variation has important implications, including the potential not only to reduce the degree of intra-specific competition, but also to increase individual efficiency in finding and handling food (Estes et al 2003, Cook et al 2006, Kotzerka et al 2011. Moreover, if a wide range of habitats and resources are used, a particular species or population may be better buffered against anthropogenic impacts, as individuals are likely to respond in different ways to changes in the environment (Tinker et al 2008, Dias et al 2011, Masello et al 2013. Hence, the characterisation of divergent behaviour or strategies may provide important in sights into the ecology, evolution, conservation and management of the species (Thiemann et al 2011, Wakefield et al 2015, Ramírez et al 2016.…”