Asymmetric Competition, Habitat Selection, and Niche Overlap in Juvenile Salmonids

Abstract

The relationship among asymmetric competition, habitat selection, and niche overlap is poorly understood. I conducted a response surface design experiment in artificial stream channels using juvenile coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) to explore the density‐ and scale‐dependent relationship among asymmetric competition, habitat selection, and niche overlap. In these sympatric populations, juvenile coho are larger, occupy mutually preferred deep, low‐velocity pools, and displace steelhead into shallow, high‐velocity riffles. I measured habitat selection over a wide range of species' densities under two competitive scenarios: coho larger than steelhead (natural size asymmetry), and species size matched (natural size asymmetry removed). When coho had their natural size advantage, interspecific competition was strongly asymmetric, and habitat selection by both species depended primarily on coho density. Removing the size advantage of coho reduced by half the per capita effect of coho on steelhead habitat selection, which was then affected similarly by intra‐ and interspecific competition. However, habitat selection by coho still depended more on intra‐ than interspecific competition. The effect of asymmetric competition on niche overlap was density‐ and scale‐dependent. Asymmetric competition reduced niche overlap nonsignificantly across all densities at the habitat type scale (pools, riffles). At the microhabitat scale (velocity, distance, depth), asymmetric competition reduced niche overlap at low, but not high, densities. Because I manipulated the competitive asymmetry in a single sympatric species pair, this experiment alters a competitive interaction while controlling for evolutionary history and thus provides a direct test of the effect of asymmetric competition on habitat selection and niche overlap. Combining a response surface design with different measures of niche overlap reveals how this effect can be both density‐ and scale‐dependent.

Abiotic habitat thresholds for salmonid over‐summer survival in intermittent streams

“…Conductivity can serve as a proxy for disconnection time (Boulton andLake 1990, Lake 2003 The interaction between surface area and initial salmonid count is a proxy for density, which may reduce growth via competition (Young 2004, Houde et al 2015) † Removed from logistic regression analysis due to strong correlation with minimum (maximum depth) and minimum surface area.…”

“…Bugert and Bjornn (1991) and Young (2004) found that steelhead often occur in shallower water habitats and may be excluded from preferred deep water habitats by the larger coho juveniles. In intermittent streams, this competitive exclusion at the reach scale in early summer may cause steelhead to become trapped in shallow pools after riffles become disconnected.…”

Ecological segregation of bark beetle (Coleoptera, Curculionidae, Scolytinae) infested Scots pine

“…Although many studies have addressed the effects of biotic interactions on the populations of species from different taxonomic groups (e.g. Mysterud 2000;Julliard et al 2006;Dole´dec et al 2008;Young 2008), only a few publications have been conducted related to bark beetles. A few studies describe the biotic interactions of insects from the subfamily Scolytinae in spruce Picea abies L.…”

Selección denso-dependiente de microhabitat en Galaxias platei: un estudio experimental

“…La conducta que describimos en cuanto al uso de mayor refugio por G. platei es similar a la reportada para especies de salmónidos (Young 2004;Amstrong & Griffi ths 2001;Rangeley & Kramer 1998). En este sentido, es interesante plantearse cómo se manifi esta la relación interespecífi ca entre dos o más especies (e.g.…”