Interacting effects of density and temperature on body size in multiple populations of Chinook salmon

Abstract

Summary1. The size individuals attain reflects complex interactions between food availability and quality, environmental conditions and ecological interactions. A statistical interaction between temperature and the density of conspecifics is expected to arise from various ecological dynamics, including bioenergetic constraints, if population density affects mean consumption rate or activity level. Density effects on behaviour or size-selective predation could also generate this pattern. This interaction plays an important role in bioenergetic models, in particular, and yet has not been documented in natural populations. 2. The lengths of 131 286 juvenile wild Chinook salmon (Oncorhynchus tshawytscha) across 13 populations spread throughout the Salmon River Basin, Idaho, USA over 15 years were compared to test whether juvenile density alters the relationship between body size and temperature. 3. Strong evidence for a negative interaction between mean summer temperature and density emerged, despite the relatively cool temperatures in this high elevation habitat. Growth correlated positively with temperature at lower densities, but the correlation was negative at the highest densities. 4. This is the first study to document this interaction at such a large spatial and temporal scale, and suggests that warmer temperatures might intensify some density-dependent processes. How climate change will affect individual growth rates in these populations will depend intimately on ecological conditions, particularly food availability and population dynamics. More broadly, the conditions that led to the interactions observed in our study -limited food availability and temperatures that ranged above those optimal for growth -likely exist for many other natural populations, and warrant broader exploration.

Density dependence and its impact on individual growth rates in an age‐structured stream salmonid population

“…Whereas we did not find any conclusive effects of temperature and density interactions on juvenile steelhead growth rates, Crozier et al (2010) found that the negative effects of density on individual Chinook salmon (O. tshawytscha) size were exacerbated at high temperatures, and that growth correlated positively to temperature at relatively low densities. Parra et al (2012) reported on a positive relationship between temperature and size early in ontogeny, and that density-dependent effects posed more important constraints on the size of larger brown trout.…”

“…The interacting effects of density and temperature have been studied in several recent works (Crozier et al 2010, Parra et al 2012, Baerum et al 2013, and reveal complex constraints on individual growth and size-at-age. Whereas we did not find any conclusive effects of temperature and density interactions on juvenile steelhead growth rates, Crozier et al (2010) found that the negative effects of density on individual Chinook salmon (O. tshawytscha) size were exacerbated at high temperatures, and that growth correlated positively to temperature at relatively low densities.…”

“…We included water temperature as a level-2 covariate. We considered temperature alone, and as an interaction with density (Crozier et al 2010, Baerum et al 2013, both as random intercept models. The structure of the first model, with only temperature as a predictor, is the same as Eq.…”

“…However, with the potentially strong influence of density on individual growth rates, and the consequences for life history expression and fitness, it is important to understand the extent to which density dependence is manifested at the individual level (Sogard 1997, DeAngelis and Mooij 2005, Kaspersson et al 2013. These effects can be particularly important in age-structured populations, in which the presence of one cohort can alter the behavior of another (Rosenfeld andBoss 2001, Kaspersson andHö jesjö 2009), and in populations experiencing abiotic conditions which can exacerbate the effects of competition (Crozier et al 2010, Parra et al 2012). Here we study the effects of population density on individual growth rates in juvenile age classes of steelhead (Oncorhynchus mykiss) in a population listed as threatened under the Endangered Species Act (NMFS 2010).…”

Developing a broader scientific foundation for river restoration: Columbia River food webs

“…and Caspian terns (Hydroprogne caspia) on migrating juvenile salmon (63)(64)(65)(66), impacts of nonnative mysids and lake trout on kokanee and native salmonids in lakes (28,67), complex species interactions (68), and stage-specific growth and survival of some juvenile salmon populations during freshwater and early marine rearing (69,70). General statistical and population models have been used to explore density dependence and carrying capacities in lakeand stream-rearing populations (71)(72)(73)(74). More broadly, trophic modeling has greatly improved the understanding of lake conditions in North America (20,26).…”