5. Hepp, M; Palsson, E; Thomsen, SK; Green, DJ. (2021) Predicting the effects of reservoir water level management on the reproductive output of a riparian songbird.PLoS One 16 Predicting the effects of reservoir water level management on the reproductive output of a riparian songbird
Dams and reservoirs alter natural water flow regimes with adverse effects on natural ecosystems. Quantifying and reducing these effects are important as global demands for energy and water, and the number of dams and reservoir, increase. However, costs and logistic constraints typically preclude experimental assessment of reservoir effects on the environment. We developed a stochastic individual-based model (IBM), parameterized using empirical data, to estimate the annual productivity of yellow warblers that breed in riparian habitat within the footprint of the Arrow Lakes Reservoir in British Columbia, Canada. The IBM incorporated information on breeding phenology, nest site selection, brood parasitism, daily nest survival, re-nesting probabilities and post-fledging survival. We used the IBM to estimate the effect of four different water management scenarios on annual productivity. We found that the IBM accurately estimated average nest success (0.39 +/- 0.10 SD), the proportion of females that produced at least one fledgling during a breeding season (0.56 +/- 0.11), and annual fledging success (2.06 +/- 0.43) under current conditions. The IBM estimated that reservoir operations currently reduce the annual productivity of this population by 37%, from an average of 1.62 to 1.06 independent young/female. Delaying when reservoir water levels reach 435m asl (the minimum elevation occupied by yellow warblers) by approximately 2 weeks was predicted to increase annual productivity to 1.44 independent young/female. The standardized effect on annual productivity of reducing the maximum elevation of the reservoir so that yellow warbler habitat is not inundated (Cohen's d = 1.52) or delaying when water is stored (Cohen's d = 0.83) was primarily driven by inundation effects on post-fledging survival. Reservoir operation effects on breeding birds will be species specific, but this IBM can easily be modified to allow the environmental impacts on the entire breeding bird community to be incorporated into water management decisions. DOI PubMed
4. Macfarland, L; Mahony, NA; Harrison, M; Green, D. (2019) Habitat-mediated breeding performance of Lewis's Woodpeckers (Melanerpes lewis) in British Columbia.PLoS One 14 Habitat-mediated breeding performance of Lewis's Woodpeckers (Melanerpes lewis) in British Columbia
Tree cavities provide a critical resource for cavity-nesting animals, and high quality cavities can be difficult for animals to acquire in habitats where competition is high. We investigated the breeding performance of Lewis's Woodpeckers in three habitat types in British Columbia, Canada in 2013 and 2014. We also assessed whether the number of nest competitors and cavity availability influenced the habitat specific breeding performance of this threatened cavity nesting species. We found that daily nest survival rate was lower in burned habitat (0.15 +/- 0.08 (0.05-0.37)) than in live pine (0.72 +/- 0.10 (0.51-0.87)) or cottonwood (0.69 +/- 0.09 (0.51-0.83)) habitats. However, hatching success (the proportion of eggs that hatch) was lower in live pine habitat (0.59 +/- 0.09 95% CI) than burned (0.77 +/- 0.19 95% CI) or cottonwood (0.80 +/- 0.07 95% CI) habitat, and the fledging success of successful nests in live pine and burned habitat (1.86 +/- 0.31 and 1.88 +/- 0.59 95% CI, respectively) was slightly lower than in cottonwood habitat (2.61 +/- 0.45 95% CI). Consequently, Lewis's Woodpeckers in cottonwood habitat produced more fledglings per nesting attempt (2.05 +/- 0.49 95% CI) than in live pine (1.53 +/- 0.35 95% CI) or burned (0.79 +/- 0.49 95% CI) habitat. Habitats differed in the number of nesting competitors and the number of suitable cavities surrounding active Lewis's Woodpecker nests. Our results showed that cavity density best explained breeding performance differences although the mechanisms remain unclear. There was no evidence that the number of heterospecific nest competitors, including the invasive European Starling (Sturnus vulgaris), explained or influenced Lewis's Woodpecker breeding performance. Cavity density influenced the productivity of successful nests but did not explain habitat differences in hatching success or daily nest survival. Further work is required to understand the mechanistic basis for the habitat specific breeding performance of Lewis's Woodpeckers. Habitat differences in breeding performance in British Columbia are not consistent with those in other regions, highlighting the importance of regionally-specific demographic data for managing species at risk. DOI PubMed
3. Thomsen, SK; Mazurkiewicz, DM; Stanley, TR; Green, DJ. (2018) El Nino/Southern Oscillation-driven rainfall pulse amplifies predation by owls on seabirds via apparent competition with mice.Proc. R. Soc. B-Biol. Sci. 285 El Nino/Southern Oscillation-driven rainfall pulse amplifies predation by owls on seabirds via apparent competition with mice
El Nino/Southern Oscillation; predator-mediated apparent competition; predation; marine-terrestrial links; rainfall; mathematical model
Most approaches for assessing species vulnerability to climate change have focused on direct impacts via abiotic changes rather than indirect impacts mediated by changes in species interactions. Changes in rainfall regimes may influence species interactions from the bottom-up by increasing primary productivity in arid environments, but subsequently lead to less predictable top-down effects. Our study demonstrates how the effects of an EL Nino/Southern Oscillation (ENSO)-driven rainfall pulse ricochets along a chain of interactions between marine and terrestrial food webs, leading to enhanced predation of a vulnerable marine predator on its island breeding grounds. On Santa Barbara Island, barn owls (Tyto alba) are the main predator of a nocturnal seabird, the Scripps's murrelet (Synthliboramphus scrippsi), as well as an endemic deer mouse. We followed the links between rainfall, normalized difference vegetation index and subsequent peaks in mouse and owl abundance. After the mouse population declined steeply, there was approximately 15-fold increase in the number of murrelets killed by owls. We also simulated these dynamics with a mathematical model and demonstrate that bottom-up resource pulses can lead to subsequent declines in alternative prey. Our study highlights the need for understanding how species interactions will change with shifting rainfall patterns through the effects of ENSO under global change. DOI PubMed
2. van den Top, GG; Reynolds, JD; Prins, HHT; Mattsson, J; Green, DJ; Ydenberg, RC. (2018) From salmon to salmonberry: The effects of salmon-derived nutrients on the stomatal density of leaves of the nitriphilic shrub Rubus spectabilis.Funct. Ecol. 32 From salmon to salmonberry: The effects of salmon-derived nutrients on the stomatal density of leaves of the nitriphilic shrub Rubus spectabilis
Great Bear Rainforest; nutrient subsidy; Rubus spectabilis; salmonberry; salmon-derived nutrients; stomata; stomatal density
Nutrients derived from the carcasses of Pacific salmon have been shown to have wide-ranging effects on riparian systems. These include changes in community species composition and an increase in leaf nitrogen concentration, with the latter effect pronounced in the nitriphilic shrub Rubus spectabilis (salmonberry). Experimental work with other species has shown that leaf stomatal density increases in response to nitrogen fertilization. We predicted that the stomatal density of salmonberry leaves would vary directly with the density of spawning salmon in salmonberry leaves collected from 16 streams in the vicinity of Bella Bella, on British Columbia's central coast. We estimated the stomatal density along each stream, and quantified stream characteristics, including the number of spawning salmon (Oncorhynchus spp.), canopy cover, stem density and soil moisture. We found that salmon have both direct and indirect effects on stomatal density, the latter mediated by canopy cover and stem density. Salmonberry stomatal density increased by 1.12 stomata per mm(2) (similar to 0.5%) for every kg of salmon per metre of stream. Over the range of salmon densities observed (1.8-49.0 kg per metre of stream), stomatal density increased by almost 45 mm(-2), or more than 20%. These data confirm that the stomatal density in salmonberry responds positively to the opportunity for greater productivity provided by salmon carcasses. The data provide insight into the physiological and morphological processes supporting nitrogen uptake, which in turn influences plant community composition. A is available for this article. DOI
1. Thomsen, SK; Green, DJ. (2016) Cascading effects of predation risk determine how marine predators become terrestrial prey on an oceanic island.Ecology 97: 3530-3537 Cascading effects of predation risk determine how marine predators become terrestrial prey on an oceanic island
apex predators; barn owls; deer mice; giving up densities; indirect interactions; mesopredators; murrelets; predation; risk effects; seabirds; trophic cascade
Apex predators can suppress the foraging activity of mesopredators, which may then result in cascading benefits for the prey of those mesopredators. We studied the interactions between a top predator, the Barn Owl (Tyto alba), and their primary prey, an island endemic deer mouse (Peromyscus maniculatus elusus), which in turn consumes the eggs of seabirds nesting on Santa Barbara Island in California. Scripps's Murrelets (Synthliboramphus scrippsi), a threatened nocturnal seabird, arrive annually to breed on this island, and whose first egg is particularly vulnerable to predation by mice. We took advantage of naturally occurring extreme variations in the density of mice and owls on the island over 3 years and predicted that (1) mouse foraging would decrease with increasing predation risk from owls and moonlight and (2) these decreases in foraging would reduce predation on murrelet eggs. We measured the giving up densities of mice with experimental foraging stations and found that mice were sensitive to predation risk and foraged less when owls were more abundant and less during the full moon compared to the new moon. We also monitored the fates of 151 murrelet eggs, and found that murrelet egg predation declined as owl abundance increased, and was lower during the full moon compared to the new moon. Moreover, high owl abundance suppressed egg predation even when mice were extremely abundant. We conclude that there is a behaviorally mediated cascade such that owls on the island had a positive indirect effect on murrelet egg survival. Our study adds to the wider recognition of the strength of risk effects to structure food webs, as well as highlighting the complex ways that marine and terrestrial food webs can intersect. DOI
