Rechsteiner EU et al. (2019), Sex and occupation time influence niche space o...

ECB-ART-47117

Ecol Evol 2019 Mar 01;96:3321-3334. doi: 10.1002/ece3.4953.

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Sex and occupation time influence niche space of a recovering keystone predator.

Rechsteiner EU , Watson JC , Tinker MT , Nichol LM , Morgan Henderson MJ , McMillan CJ , DeRoos M , Fournier MC , Salomon AK , Honka LD , Darimont CT .

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Predators exert strong effects on ecological communities, particularly when they re-occupy areas after decades of extirpation. Within species, such effects can vary over time and by sex and cascade across trophic levels. We used a space-for-time substitution to make foraging observations of sea otters (Enhydra lutris) across a gradient of reoccupation time (1-30 years), and nonmetric multidimensional scaling (nMDS) analysis to ask whether (a) sea otter niche space varies as a function of occupation time and (b) whether niche space varies by sex. We found that niche space varied among areas of different occupation times. Dietary niches at short occupation times were dominated by urchins (Mesocentrotus and Strongylocentrotus spp; >60% of diets) in open habitats at 10-40 m depths. At longer occupation times, niches were dominated by small clams (Veneroida; >30% diet), mussels (Mytilus spp; >20% diet), and crab (Decapoda; >10% diet) in shallow (<10 m) kelp habitats. Diet diversity was lowest (H'' = 1.46) but energy rich (~37 kcal/min) at the earliest occupied area and highest, but energy poor (H'' = 2.63, ~9 kcal/min) at the longest occupied area. A similar transition occurred through time at a recently occupied area. We found that niche space also differed between sexes, with bachelor males consuming large clams (>60%), and urchins (~25%) from deep waters (>40 m), and females and territorial males consuming smaller, varied prey from shallow waters (<10 m). Bachelor male diets were less diverse (H'' = 2.21) but more energy rich (~27 kcal/min) than territorial males (H'' = 2.54, ~13 kcal/min) and females (H'' = 2.74, ~11 kcal/min). Given recovering predators require adequate food and space, and the ecological interactions they elicit, we emphasize the importance of investigating niche space over the duration of recovery and considering sex-based differences in these interactions.

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Genes referenced: LOC100887844 LOC115925415

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	Figure 1. Map of British Columbia shoreline (a) and central coast study area (b) with occupation areas (câ€“h) and observation sites (red circles)
	Figure 2. Prey consumed by sea otters at occupation areas from 1 to 30Â years occupied (YO) as proportion of diet by frequency of occurrence. Black bars show large prey, gray bars show medium prey, and white bars show small prey. Blue crossâ€hatched bars indicate mean size of prey. Red crossâ€hatched bars show energy intake. Error bars are SEM, nÂ =Â 4 for all occupation areas except McMullins where nÂ =Â 6. Hâ€² is Shannon index of diversity. For prey group abbreviations, see Table 1
	Figure 3. Prey consumed by sea otters of each sex class as proportion of diet by frequency of occurrence. Black bars show large prey, gray bars show medium prey, and white bars show small prey. Blue crossâ€hatched bars indicate mean size of prey. Red crossâ€hatched bars show energy intake. Error bars are SEM, n is number of sites, and Hâ€² is Shannon index of diversity. For prey group abbreviations, see Table 1
	Figure 4. Dendrogram of hierarchical clustering (using group average linking) of replicate observation sites at each occupation area, based on Brayâ€“Curtis dissimilarity matrix of sea otter diets. Dotted line shows 63% similarity. Grey symbols correspond to the shortest occupation time, blue symbols to medium occupation times, and red symbols to longest occupation times
	Figure 5. Nonmetric multidimensional scaling analysis plot of sea otter niche space with (a) clusters identified in Figure 4 with 63% similarity, and environmental vectors with â‰¥0.5 correlation to dissimilarities, and (b) bubble plots depicting the most common prey groups, with bubble segments approaching sizes of segments in the legend representing ~80% of the diet by frequency of occurrence
	Figure 6. Dendrogram of hierarchical clustering (using group average linking) of replicate observation sites for each sex, based on Brayâ€“Curtis dissimilarity matrix of sea otter diets. Dotted line shows 45% similarity
	Figure 7. Nonmetric multidimensional scaling analysis (nMDS) plot of sea otter niche space with (a) clusters identified in Figure 6 with 45% similarity, and environmental vectors with â‰¥0.5 correlation to dissimilarities, and (b) bubble plots depicting the most common prey groups, with bubble segments approaching sizes of segments in the legend representing ~80% of the diet by frequency of occurrence

References [+] :

Baudrot, The adaptation of generalist predators' diet in a multi-prey context: insights from new functional responses. 2016, Pubmed