Intraspecific competition drives increased resource use diversity within a natural population

Abstract

Resource competition is thought to play a major role in driving evolutionary diversification. For instance, in ecological character displacement, coexisting species evolve to use different resources, reducing the effects of interspecific competition. It is thought that a similar diversifying effect might occur in response to competition among members of a single species. Individuals may mitigate the effects of intraspecific competition by switching to use alternative resources not used by conspecific competitors. This diversification is the driving force in some models of sympatric speciation, but has not been demonstrated in natural populations. Here, we present experimental evidence confirming that competition drives ecological diversification within natural populations. We manipulated population density of three-spine sticklebacks (Gasterosteus aculeatus) in enclosures in a natural lake. Increased population density led to reduced prey availability, causing individuals to add alternative prey types to their diet. Since phenotypically different individuals added different alternative prey, diet variation among individuals increased relative to low-density control enclosures. Competition also increased the diet-morphology correlations, so that the frequency-dependent interactions were stronger in high competition. These results not only confirm that resource competition promotes niche variation within populations, but also show that this increased diversity can arise via behavioural plasticity alone, without the evolutionary changes commonly assumed by theory.

Competition-driven speciation in cichlid fish

“…It remains to be established whether this is a consequence of exploitation competition, where individuals compete indirectly and passively and for limited resources [29][30][31][32][33] , or interference competition, where individuals compete directly often using aggression 34 . It is most parsimonious that interference competition is dominant in this system, as intraspecific territorial control via aggression is well known in cichlids, including lamprologines 35 .…”

Cultural transmission of tool use by Indo-Pacific bottlenose dolphins (Tursiopssp.) provides access to a novel foraging niche

“…B 281: 20140374 is indeed associated with the continued exploitation of an otherwise unused niche. Niche theory suggests that foraging specializations are ultimately driven by intraspecific competition or by trade-offs related to either habitat heterogeneity or phenotypic differences [1,[45][46][47]. The exploitation of otherwise unused resources can be beneficial as it offers a competitive refuge from conspecifics [4].…”

Intraspecific genetic variation and competition interact to influence niche expansion

“…This was shown experimentally in Drosophila populations maintained at high densities (high intraspecific competition), which evolved tolerance to food containing toxic cadmium chloride more rapidly than populations at lower densities (Bolnick 2001). Experimentally elevated intraspecific competition also led to niche expansion in stickleback fish kept in enclosures in natural habitat, though the shift was behavioural rather than genetic (Svanbäck & Bolnick 2007). Further, studies with spadefoot toads and sea otters show that intraspecific competition facilitates variation in resource use (Pfennig et al 2007;Tinker et al 2008;Martin & Pfennig 2009).…”