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Ecological release from interspecific competition leads to decoupled changes in population and individual niche width.

Bolnick DI, Ingram T, Stutz WE, Snowberg LK, Lau OL, Paull JS - Proc. Biol. Sci. (2010)

Bottom Line: This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced.In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation.Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales.

View Article: PubMed Central - PubMed

Affiliation: Section of Integrative Biology, University of Texas at Austin, TX 78712, USA. danbolnick@mail.utexas.edu

ABSTRACT
A species's niche width reflects a balance between the diversifying effects of intraspecific competition and the constraining effects of interspecific competition. This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced. The resulting ecological release permits population niche expansion, via increased individual niche widths and/or increased among-individual variation. We report an experimental test of the theory of ecological release in three-spine stickleback (Gasterosteus aculeatus). We factorially manipulated the presence or absence of two interspecific competitors: juvenile cut-throat trout (Oncorhynchus clarki) and prickly sculpin (Cottus asper). Consistent with the classic niche variation hypothesis, release from trout competition increased stickleback population niche width via increased among-individual variation, while individual niche widths remained unchanged. In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation. Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales. Importantly, we find that changes in population niche width are decoupled from changes in the niche widths of individuals within the population.

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Effect of competitor removal on the degree of individual specialization in stickleback (WIC/TNW). When WIC/TNW = 1, individuals have the same niche breadth as the population as a whole. As WIC/TNW gets smaller, individuals are increasingly specialized relative to their population and between-individual variation is proportionally larger. Each point is the average value for a given block of enclosures, averaging across the other competitor treatments. Lines connect competitor-present versus competitor-absent results for a given block. Blocks are also colour-coded to permit comparisons across (a) and (b) and with other figures. We do not illustrate the non-significant interaction between trout and sculpin removal.
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RSPB20100018F4: Effect of competitor removal on the degree of individual specialization in stickleback (WIC/TNW). When WIC/TNW = 1, individuals have the same niche breadth as the population as a whole. As WIC/TNW gets smaller, individuals are increasingly specialized relative to their population and between-individual variation is proportionally larger. Each point is the average value for a given block of enclosures, averaging across the other competitor treatments. Lines connect competitor-present versus competitor-absent results for a given block. Blocks are also colour-coded to permit comparisons across (a) and (b) and with other figures. We do not illustrate the non-significant interaction between trout and sculpin removal.

Mentions: Release from interspecific competitors altered how TNW was partitioned into within- versus between-individual diversity (figure 3). Although sculpin release had no effect on TNW, it did increase individual niche breadth (WIC; p = 0.003), and decreased between-individual variation (BIC; p = 0.022). The opposing changes in WIC and BIC cancelled each other out, explaining the lack of a sculpin effect on TNW. As a result, release from sculpin competition led to reduced individual specialization in stickleback (increased WIC/TNW, p = 0.0019; figure 4). These results closely match our ‘individual release’ scenario (figure 1c). The increase in WIC/TNW is corroborated by decreased pairwise diet dissimilarity among individuals (E; sculpin effect, p = 0.0279). We found no significant sculpin × trout interactions (WIC: p = 0.147; BIC: p = 0.077; WIC/TNW: p = 0.287). There was a weak tendency towards an interaction effect for BIC: sculpin release had no significant effect on BIC when trout were present, but a strong negative effect on BIC when trout were absent.


Ecological release from interspecific competition leads to decoupled changes in population and individual niche width.

Bolnick DI, Ingram T, Stutz WE, Snowberg LK, Lau OL, Paull JS - Proc. Biol. Sci. (2010)

Effect of competitor removal on the degree of individual specialization in stickleback (WIC/TNW). When WIC/TNW = 1, individuals have the same niche breadth as the population as a whole. As WIC/TNW gets smaller, individuals are increasingly specialized relative to their population and between-individual variation is proportionally larger. Each point is the average value for a given block of enclosures, averaging across the other competitor treatments. Lines connect competitor-present versus competitor-absent results for a given block. Blocks are also colour-coded to permit comparisons across (a) and (b) and with other figures. We do not illustrate the non-significant interaction between trout and sculpin removal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2871882&req=5

RSPB20100018F4: Effect of competitor removal on the degree of individual specialization in stickleback (WIC/TNW). When WIC/TNW = 1, individuals have the same niche breadth as the population as a whole. As WIC/TNW gets smaller, individuals are increasingly specialized relative to their population and between-individual variation is proportionally larger. Each point is the average value for a given block of enclosures, averaging across the other competitor treatments. Lines connect competitor-present versus competitor-absent results for a given block. Blocks are also colour-coded to permit comparisons across (a) and (b) and with other figures. We do not illustrate the non-significant interaction between trout and sculpin removal.
Mentions: Release from interspecific competitors altered how TNW was partitioned into within- versus between-individual diversity (figure 3). Although sculpin release had no effect on TNW, it did increase individual niche breadth (WIC; p = 0.003), and decreased between-individual variation (BIC; p = 0.022). The opposing changes in WIC and BIC cancelled each other out, explaining the lack of a sculpin effect on TNW. As a result, release from sculpin competition led to reduced individual specialization in stickleback (increased WIC/TNW, p = 0.0019; figure 4). These results closely match our ‘individual release’ scenario (figure 1c). The increase in WIC/TNW is corroborated by decreased pairwise diet dissimilarity among individuals (E; sculpin effect, p = 0.0279). We found no significant sculpin × trout interactions (WIC: p = 0.147; BIC: p = 0.077; WIC/TNW: p = 0.287). There was a weak tendency towards an interaction effect for BIC: sculpin release had no significant effect on BIC when trout were present, but a strong negative effect on BIC when trout were absent.

Bottom Line: This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced.In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation.Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales.

View Article: PubMed Central - PubMed

Affiliation: Section of Integrative Biology, University of Texas at Austin, TX 78712, USA. danbolnick@mail.utexas.edu

ABSTRACT
A species's niche width reflects a balance between the diversifying effects of intraspecific competition and the constraining effects of interspecific competition. This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced. The resulting ecological release permits population niche expansion, via increased individual niche widths and/or increased among-individual variation. We report an experimental test of the theory of ecological release in three-spine stickleback (Gasterosteus aculeatus). We factorially manipulated the presence or absence of two interspecific competitors: juvenile cut-throat trout (Oncorhynchus clarki) and prickly sculpin (Cottus asper). Consistent with the classic niche variation hypothesis, release from trout competition increased stickleback population niche width via increased among-individual variation, while individual niche widths remained unchanged. In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation. Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales. Importantly, we find that changes in population niche width are decoupled from changes in the niche widths of individuals within the population.

Show MeSH
Related in: MedlinePlus