Individual specialization in diet by a generalist marine predator reflects specialization in foraging behaviour

Abstract

Summary 1.We studied chick diet in a known-age, sexed population of a long-lived seabird, the Brünnich's guillemot ( Uria lomvia ), over 15 years ( N = 136; 1993-2007) and attached time-depth-temperature recorders to examine foraging behaviour in multiple years ( N = 36; 2004-07). 2. Adults showed specialization in prey fed to offspring, described by multiple indices calculated over 15 years: 27% of diet diversity was attributable to among-individual variation (withinindividual component of total niche width = 0·73); average similarity of an individual's diet to the overall diet was 65% (mean proportional similarity between individuals and population = 0·65); diet was significantly more specialized than expected for 70% of individuals (mean likelihood = 0.53). These indices suggest higher specialization than the average for an across-taxa comparison of 49 taxa. 3. Foraging behaviour varied along three axes: flight time, dive depth and dive shape. Individuals showed specialized individual foraging behaviour along each axis. These foraging strategies were reflected in the prey type delivered to their offspring and were maintained over scales of hours to years. 4. Specialization in foraging behaviour and diet was greater over short time spans (hours, days) than over long time spans (years). Regardless of sex or age, the main component of variation in foraging behaviour and chick diet was between individuals. 5. Plasma stable isotope values were similar across years, within a given individual, and variance was low relative to that expected from prey isotope values, suggesting adult diet specialized across years. Stable isotope values were similar among individuals that fed their nestlings similar prey items and there was no difference in trophic level between adults and chicks. We suggest that guillemots specialize on a single foraging strategy regardless of whether chick-provisioning and self-feeding. With little individual difference in body mass and physiology, specialization likely represents learning and memorizing optimal feeding locations and behaviours. 6. There was no difference in survival or reproductive success between specialists and generalists, suggesting these are largely equivalent strategies in terms of evolutionary fitness, presumably because different strategies were advantageous at different levels of prey abundance or predictability. The development of individual specialization may be an important precursor to diversification among seabirds.

Optimal foraging in chick-raising Common Guillemots (Uria aalge)

“…It was impossible to improve this quantification due to large differences in the degree of digestion of the samples and the uncertainty as to how many meals each regurgitation represented. To avoid possible pseudoreplication through possible diet specialization by individual birds (Woo et al 2008), only one diet sample (stomach and/or chick) was collected from an adult. Means are given ±1 standard deviation.…”

Consistency pays: sex differences and fitness consequences of behavioural specialization in a wide-ranging seabird

“…[13 -15]), results are not conclusive, suggesting under some conditions, generalists are favoured [15,16]. Theoretical predictions infer that if groups experience different levels of environmental heterogeneity, the selective pressures favouring specialization may also vary [17], offering some explanation for differences between populations.…”

Diet composition and foraging success in generalist predators: Are specialist individuals better foragers?

“…Woo et al (2008), pointed out that over long periods, with fluctuating prey levels, different foraging strategies may balance out. Recent studies (van de Pol et al 2009(van de Pol et al , 2010 showed also the necessity to consider appropriate time-scale to understand the mechanism by which environmental change affects the evolution and maintenance of diet specialization.…”

“…Dietary differences among individuals may be also related to differences in foraging. For example, Woo et al (2008) showed that individual diet specialization in a Brünnich's guillemot (Uria lomvia) population was related to foraging behaviour as guillemots specialize on a single foraging strategy across years, regarding flight time, dive depth and dive shape.…”

“…Overall, the causes and correlates of individual dietary specialization are still insufficiently understood, and the higher ecological performance of individual specialists over generalist remains controversial (Dornhaus 2008;Woo et al 2008). Furthermore, relatively few studies have empirically examined the relationship between individual diet specialization and foraging success in wide-ranging vertebrate predators, as a consequence of the logistical difficulties of assessing foraging success in this type of species (but see Masman et al 1988;Tinker et al 2008;Catry et al 2014).…”