Differential tree and shrub production in response to fertilization and disturbance by coastal river otters in Alaska

Abstract

We explored the interacting effects of marine-derived nutrient fertilization and physical disturbance introduced by coastal river otters (Lontra canadensis) on the production and nutrient status of pristine shrub and tree communities in Prince William Sound, Alaska, USA. We compared production of trees and shrubs between latrines and non-latrines, while accounting for otter site selection, by sampling areas on and off sites. Nitrogen stable isotope analysis (delta15N) indicated that dominant tree and shrub species assimilated the marine-derived N excreted by otters. In association with this uptake, tree production increased, but shrub density and nonwoody aboveground shrub production decreased. The reduced shrub production was caused by destruction of ramets, especially blueberry (Vaccinium spp.), through physical disturbance by river otters. False azalea (Menziesia ferruginea) ramets were less sensitive to otter disturbance. Although surviving individual blueberry ramets showed a tendency for increased production per plant, false azalea allocated excess N to storage in leaves rather than growth. We found that plant responses to animal activity vary among species and levels of biological organization (leaf, plant, ecosystem). Such differences should be accounted for when assessing the influence of river otters on the carbon budget of Alaskan coastal forests at the landscape scale.

Estimating Leaf Area Index in Southeast Alaska: A Comparison of Two Techniques

“…Estimates of LAI from indirect measurements have ranged from 1.46–4.22 along the shorelines of western Prince William Sound, AK [13], 2.04–5.44 on Vancouver Island, British Columbia [8], and from 3.0–4.0 on the Oregon coast [50]. This is especially striking when considering the relationship between LAI measurements and BA.…”

“…In many forest types, where destructive sampling is difficult, leaf area index (LAI) can be predicted from allometric relationships between leaf area and woody stem measurements such as sapwood area or diameter at breast height (DBH) [12]. Alternatively, LAI can be indirectly measured using gap fraction analysis, although such measurements are relatively rare in coastal rainforests [8], [13]. In such environments patterns of LAI are usually inferred from studies in other somewhat similar habitats.…”

Indirect effects of bioinvasions in Yellowstone Lake: The response of river otters to declines in native cutthroat trout

“…Less often has this debate addressed the consequences of mitigating biological invasions in one ecosystem on linked ecological processes in an adjacent one. For example, river otters transfer aquatically-derived nutrients to terrestrial habitats via their scent-marking behavior at latrines and create "hot spots" of nutrient heterogeneity at the waterland interface (Ben-David et al, 2005;Crait and Ben-David, 2007;Roe et al, 2010). Our finding of behavioral changes in latrine use suggests that the spatial distribution of these hot spots may have shifted away from tributary streams.…”

Impacts of Pollutants on Beavers and Otters with Implications for Ecosystem Ramifications

“…Latrine sites are areas that are scent‐marked with feces, urine or anal gland secretions for either intra‐group communication (marked more heavily in social groups) or mutual avoidance in nonsocial groups (Ben‐David et al ). Although otter diet improves the movement of nutrients and subsequently the productivity of vegetation (Roe et al ) through increases in fish density at latrine sites (Ben‐David et al ), the physical activity of creating latrines can damage smaller plants (Roe et al ). The influx of nutrients released at river otter latrine sites varies with respect to the social nature of the otters (Ben‐David et al ); less social otters use a relatively large number of different latrine sites with infrequent revisits, whereas more social otters visit fewer latrines frequently.…”