Resource pulses increase the diversity of successful competitors in a multi‐species stream fish assemblage

Abstract

Food resources are often patchily distributed through space and time and are classified as resource pulses when hyperabundant. Resource pulses can benefit growth, reproduction, and abundance of various consumers. Yet, it is relatively unknown how such resources are partitioned among competing consumers and how this is influenced by the magnitude of the pulse. Here, we examined how the magnitude of a pulsed resource influences resource partitioning among diverse sizes and species of consumers in a natural setting over small spatial and temporal scales. We focused on salmon egg subsidies to stream fish consumers. We experimentally added different quantities of pink salmon eggs to five meter long experimental stream sections. Egg additions spanned three orders of magnitude from 6 to 3575 eggs. Stream fish (egg consumers) were captured and gastric lavaged at each experimental section to determine how many eggs each individual fish consumed. We modeled taxon‐specific individual egg consumption as a function of egg availability, individual mass, community composition, number of competitors, and stream velocity using hurdle models in a Bayesian framework. We found that there were diminishing returns for increasing egg abundance increasing egg consumption (i.e., type II functional response) for individual size classes of fish, but that higher egg numbers were needed to benefit diverse consumers. Top models indicated that egg availability and individual fish characteristics (size and taxon) drove egg consumption, while community characteristics (species composition and number of competitors) were not supported. Our results suggest that resource pulses can provide rare opportunities for less dominant sizes and species of fish to consume abundant resources. The current paradigm in the stream fish literature suggests that stream fish communities are structured by dominance hierarchies; however, dominance hierarchies may be less influential where pulsed resources comprise a large portion of the resource base.

Non‐native Chinook salmon add nutrient subsidies and functional novelty to Patagonian streams

“…Salmon‐derived nutrients enter these food webs through a wide variety of pathways. Direct consumption of salmon carcasses increases the biomass of collector and shredder invertebrates (Chaloner & Wipfli, 2002; Lessard & Merritt, 2006), and consumption of salmon eggs increases the biomass of a variety of stream fishes (Armstrong et al., 2010; Bailey & Moore, 2020; Bentley et al., 2012; Hermann et al., 2020; Scheuerell et al., 2007; Swain et al., 2014). Carcasses that are deposited in the riparian zone are heavily consumed by terrestrial insects (Hocking & Reimchen, 2002) and cause soils to accumulate nitrogen, affecting the composition of riparian plant assemblages (Hocking & Reynolds, 2011; Morris & Stanford, 2011) and enhancing the growth of spruce trees (Quinn et al., 2018).…”

Emergent trophic interactions following the Chinook salmon invasion of Patagonia

“…Furthermore, galaxiids are likely to have an indirect negative interaction with salmon due to the positive effects of salmon on trout and mink, both of which are galaxiid predators (Arismendi et al, 2012; Valenzuela et al, 2013). On the other hand, galaxiids and other native fishes might benefit from the consumption of salmon eggs and tissue; however, such consumption is likely limited because trout competitively exclude other stream fishes from salmon resources (Bailey & Moore, 2020). Throughout the southern hemisphere, galaxiids have declined as a result of salmonid introductions (Habit et al, 2010; Lintermans et al, 2020; Shelton et al, 2015; Townsend, 2003).…”

Life‐history connections to long‐term fish population trends in a species‐rich temperate river

“…Fish communities have been shown to shift at large time scales in response to climate change (Comte et al., 2021), deforestation (Brejão et al., 2018) and river regulation (Pereira et al., 2021). Communities also vary at smaller time scales in response to disturbances such as drought (Malone et al., 2022) and resource pulses (Bailey & Moore, 2020). How individual species respond to disturbances may be mediated by various ‘traits’, such as life‐history strategies, feeding behaviours and spawning behaviours (McLean et al., 2019).…”