Ontogenetic niche shifts in two populations of juvenile threespine stickleback, Gasterosteus aculeatus, that differ in pelvic spine morphology

Abstract

Most research on ontogenetic niche shifts has focused on changes in habitat or resource use related to food resource distribution and heterospecific size‐limited predation. Cannibalism, an intraspecific interaction, can also affect habitat selection or resource use by vulnerable size classes. Morphological defenses, such as spines, increase the effective size of an individual, making it more difficult to consume. The importance of such defense structures in affecting niche shifts in early life history stages is unclear. Using a combination of field observations and experiments in aquaria and wading pools, we examined the relative roles of cannibalism and morphology in determining juvenile habitat use in two populations of threespine stickleback that differ in pelvic spine morphology. Juveniles were categorized into three size classes: small (5–10 mm), medium (11–15 mm), and large (15–25 mm). In experiments assessing the relative vulnerability of juveniles to cannibalism by adults, we documented a significant difference among size classes in the number of juveniles eaten such that more large juveniles were eaten from the population lacking pelvic spines. The natural distribution of small and large juveniles in two distinct littoral microhabitats, open water and vegetation, was determined in each lake. In both populations, small juveniles were more abundant in vegetation. In the population with pelvic spines, a greater proportion of large juveniles was observed in open water than in vegetation. In the population without pelvic spines, the proportion of large juveniles did not differ between the two habitats. Experiments comparing juvenile habitat use in the presence or absence of adult conspecifics suggest that differences in habitat use may not only depend on the size of the individual, or the size of the individual relative to the size of the adult predator, but also on the degree of development or expression of defensive structures.

Habitat-mediated cannibalism and microhabitat restriction in the stream invertebrate Gammarus pulex

“…Our results suggest that small G. pulex may be more vulnerable to cannibalism in homogeneous and poor quality natural environments since they require refuge substrates for survival and are willing to leave refuges to obtain food when forced to make a choice. Habitat complexity has previously been associated with reduction of predation risk for vulnerable individuals (Sillett & Foster, 2000), including G. pulex, which selected complex habitats that provided refuge from predators (Dahl & Greenberg, 1996). Lowquality habitat forces prey to move between refuge habitat and more productive foraging areas, and by doing so increases their risk of predation (Sih, 1992).…”

Effects of Turbidity, Light Level, and Cover on Predation of White Sturgeon Larvae by Prickly Sculpins

“…This is probably because by about 20 mm TL white sturgeon have absorbed their yolk sac and it is necessary for them to more actively search for food (Deng et al 2002). Studies have shown that older individuals of other fish species are less likely to use cover (Sillett and Foster 2000;Laegdsgaard and Johnson 2001) because more developed fish have more advanced predator avoidance abilities (Paradis et al 1996;Williams et al 1996;Brooking et al 1998).…”

“…It has often been shown that more complex habitats provide fishes cover from predation (Wahl 1995;Bartholomew et al 2000). Furthermore, smaller individuals of some fish species are more likely to use shelter than larger fishes (Sillett and Foster 2000;Laegdsgaard and Johnson 2001). It has been documented that white sturgeon use different substrates throughout early development; newly hatched larvae settle predominantly on cobble, while older larvae and juveniles primarily prefer sand (Parsley et al 1993).…”

Limited flooding tolerance of juveniles restricts the distribution of adults in an understory shrub (Itea virginica; Iteaceae)

“…Furthermore, niche breadth can expand or contract through life history, though little is known about how ontogenetic changes in stress tolerance or niche influence the distribution of plant species (Parish and Bazzaz, 1985; Dalling et al, 2001; Eriksson, 2002; Miriti, 2006). The paucity of empirical studies on the importance of life history in defining the niche of plants contrasts starkly with the numerous studies of animals, where ontogenetic shifts in diet, morphology, and trophic interactions have been described (e.g., Sillett and Foster, 2000; Post, 2003). Nevertheless, the importance of the regeneration niche (sensu Grubb, 1977) is readily appreciated for plants.…”

“…For example, plants can vary in light requirements and water‐use through life history (Donovan and Ehleringer, 1992; Dalling et al, 2001). Size influences phenotypic expression and the way in which individuals interact with the environment for both animals and plants (Donovan and Ehleringer, 1992; Coleman et al, 1994; Sillett and Foster, 2000). For example, in arid habitats, adults with deep taproots are more adept at exploiting stable water sources than are shallowly rooted seedlings (Donovan and Ehleringer, 1992); thus conditions suitable for adults may be inhospitable for juveniles.…”