Impacts of Salmon on Riparian Plant Diversity

Abstract

The study of natural gradients in nutrient subsidies between ecosystems allows for predictions of how changes in one system can affect biodiversity in another. We performed a large-scale empirical test of the role of Pacific salmon (Oncorhynchus spp.) in structuring riparian plant communities. A comparison of 50 watersheds in the remote Great Bear Rainforest of British Columbia's central coast in Canada shows that salmon influence nutrient loading to plants,shifting plant communities toward nutrient-rich species, which in turn decreases plant diversity.These effects are mediated by interactions between salmon density and the physical characteristics of watersheds. Predicting how salmon affect terrestrial ecosystems is central to conservation plans that aim to better integrate ecosystem values into resource management.

From earth and ocean: investigating the importance of cross‐ecosystem resource linkages to a mobile estuarine consumer

“…We limited our analyses to chum and pink salmon because these species account for 90-100% of total adult salmon spawners within study sites. Detailed descriptions of salmon enumeration and estimates of population sizes can be found in Hocking and Reynolds (2011).…”

“…Each study reach length was determined by multiplying the mean stream bankfull width by 30 (Bain and Stevenson 1999). Alder basal area was calculated from the diameter at breast height for each tree greater than 5 cm in diameter in six 35 m long by 10 m wide belt transects that extended perpendicular from each stream into the riparian zone (Hocking and Reynolds 2011). Percent alder was calculated for each site as:…”

“…This also allowed us to let regression intercepts vary between sites to account for extraneous sitelevel differences that may have influenced trends, to control for the correlation of individuals from the same site between sample years, and to account for heterogeneity in the variance structure (Zuur et al 2009). Random, correlation, and variance structures were established from residuals of the global model, or models including all variables considered, and by using AICc selection of the most parsimonious structures with the global model using restricted maximum likelihood (REML) estimation (Zuur et al 2009, Hocking andReynolds 2011). For both d 15 N and d 13 C analyses, the random effect of site, the auto-correlation structure of site within year, and the variance structure of estuary size, accounted for pseudo-replication, satisfied the assumptions of residual normality and equal variance, and improved the likelihood of the global model (Zuur et al 2009).…”

“…Externally derived nutrients can influence the productivity and structure of ecosystems ranging from oceanic islands to freshwater ecosystems (Stapp and Polis 2003, Anderson et al 2008, Moore et al 2008, Richardson et al 2009, Wipfli and Baxter 2010. However, responses vary depending on the nature of a subsidy, the physical characteristics of donor and recipient systems, and the mechanisms or capacities of connectivity between them (Yang et al 2008, Hocking and Reynolds 2011, Marcarelli et al 2011. Nutrient subsidies can further be mediated by the traits of individuals or species in recipient habitats such as mobility, spatial distribution, phenology, feeding ecology and body size (Polis et al 1997, Anderson et al 2008, Hocking et al 2013.…”

How large herbivores subsidize aquatic food webs in African savannas

“…), wolves (Canis lupus), and other terrestrial carnivores and scavengers, which kill as many as 40-50% of the salmon (7,8) and transport the marine-derived nutrients onto land in the form of urine, feces, and uneaten fish scraps. These inputs have transformative effects on riparian ecosystems, supplying up to a quarter of the nitrogen budget, enriching the foliage, increasing plant growth rates, shifting the species composition of vegetation assemblages (6)(7)(8), and perhaps even locally depressing the densities of moose by inflating the number of wolves (9).…”