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Diversity of larger consumers enhances interference competition effects on smaller competitors.

Nascimento FJ, Karlson AM, Näslund J, Elmgren R - Oecologia (2010)

Bottom Line: Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon.With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments.Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

View Article: PubMed Central - PubMed

Affiliation: Department of Systems Ecology, Stockholm University, Stockholm, Sweden. francisco@ecology.su.se

ABSTRACT
Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0-3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods' incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

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Isotope values (±SE) for aC. neglecta (n = 5); bP. fennica (n = 7); cH. sorbyana (n = 7) in treatments with different combinations of macrofauna species. NoMac no macrofauna; MaM. affinis alone; PfP. femorata alone; MbM. balthica alone; Ma + PfM. affinis + P. femorata; Ma + MbM. affinis + M. balthica; Ma + Pf + Mb all three macrofauna species; Initial natural isotope values before experiment. Different letters indicate significant differences (nested ANOVA) in nitrogen isotope values among treatments for the three species (P < 0.05). Statistical differences in carbon isotope values followed the same pattern but are not shown here (see text for statistical details)
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Fig1: Isotope values (±SE) for aC. neglecta (n = 5); bP. fennica (n = 7); cH. sorbyana (n = 7) in treatments with different combinations of macrofauna species. NoMac no macrofauna; MaM. affinis alone; PfP. femorata alone; MbM. balthica alone; Ma + PfM. affinis + P. femorata; Ma + MbM. affinis + M. balthica; Ma + Pf + Mb all three macrofauna species; Initial natural isotope values before experiment. Different letters indicate significant differences (nested ANOVA) in nitrogen isotope values among treatments for the three species (P < 0.05). Statistical differences in carbon isotope values followed the same pattern but are not shown here (see text for statistical details)

Mentions: The ostracod isotope values at the end of the experiment showed that all three species had incorporated cyanobacterial N and C, with significant differences among treatments (Fig. 1). Ostracod stable N isotope values often decreased markedly, indicating decreased incorporation of cyanobacterial N, when a macrofaunal species was present in the experimental sediments, but this depended greatly on identity of the species (nested ANOVA, composition: F3,23 = 9.34, P = 0.0003 for C. neglecta; F3,42 = 16.7, P < 0.00001 for P. fennica; F3,42 = 8.6, P = 0.0001 for H. sorbyana). In addition, increased macrofaunal species richness significantly decreased the nitrogen isotope values for all ostracod species, again indicating lower incorporation of cyanobacterial N (F3,23 = 21.1, P < 0.00001, for C. neglecta; F3,42 = 23.0, P < 0.00001 for P. fennica; F3,42 = 27.6, P < 0.00001 for H. sorbyana). Similar decreases were found for carbon isotope values, but while macrofaunal species richness significantly lowered the carbon isotope values (nested ANOVA, F3,23 = 0.21, P = 0.0001 for C. neglecta; F3,42 = 36.4, P < 0.00001 for P. fennica; F3,42 = 16.3, P < 0.00001 for H. sorbyana), the effect of species composition on δ13C values was significant only for P. fennica (nested ANOVA, F3,42 = 21.3, P < 0.00001).Fig. 1


Diversity of larger consumers enhances interference competition effects on smaller competitors.

Nascimento FJ, Karlson AM, Näslund J, Elmgren R - Oecologia (2010)

Isotope values (±SE) for aC. neglecta (n = 5); bP. fennica (n = 7); cH. sorbyana (n = 7) in treatments with different combinations of macrofauna species. NoMac no macrofauna; MaM. affinis alone; PfP. femorata alone; MbM. balthica alone; Ma + PfM. affinis + P. femorata; Ma + MbM. affinis + M. balthica; Ma + Pf + Mb all three macrofauna species; Initial natural isotope values before experiment. Different letters indicate significant differences (nested ANOVA) in nitrogen isotope values among treatments for the three species (P < 0.05). Statistical differences in carbon isotope values followed the same pattern but are not shown here (see text for statistical details)
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3094539&req=5

Fig1: Isotope values (±SE) for aC. neglecta (n = 5); bP. fennica (n = 7); cH. sorbyana (n = 7) in treatments with different combinations of macrofauna species. NoMac no macrofauna; MaM. affinis alone; PfP. femorata alone; MbM. balthica alone; Ma + PfM. affinis + P. femorata; Ma + MbM. affinis + M. balthica; Ma + Pf + Mb all three macrofauna species; Initial natural isotope values before experiment. Different letters indicate significant differences (nested ANOVA) in nitrogen isotope values among treatments for the three species (P < 0.05). Statistical differences in carbon isotope values followed the same pattern but are not shown here (see text for statistical details)
Mentions: The ostracod isotope values at the end of the experiment showed that all three species had incorporated cyanobacterial N and C, with significant differences among treatments (Fig. 1). Ostracod stable N isotope values often decreased markedly, indicating decreased incorporation of cyanobacterial N, when a macrofaunal species was present in the experimental sediments, but this depended greatly on identity of the species (nested ANOVA, composition: F3,23 = 9.34, P = 0.0003 for C. neglecta; F3,42 = 16.7, P < 0.00001 for P. fennica; F3,42 = 8.6, P = 0.0001 for H. sorbyana). In addition, increased macrofaunal species richness significantly decreased the nitrogen isotope values for all ostracod species, again indicating lower incorporation of cyanobacterial N (F3,23 = 21.1, P < 0.00001, for C. neglecta; F3,42 = 23.0, P < 0.00001 for P. fennica; F3,42 = 27.6, P < 0.00001 for H. sorbyana). Similar decreases were found for carbon isotope values, but while macrofaunal species richness significantly lowered the carbon isotope values (nested ANOVA, F3,23 = 0.21, P = 0.0001 for C. neglecta; F3,42 = 36.4, P < 0.00001 for P. fennica; F3,42 = 16.3, P < 0.00001 for H. sorbyana), the effect of species composition on δ13C values was significant only for P. fennica (nested ANOVA, F3,42 = 21.3, P < 0.00001).Fig. 1

Bottom Line: Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon.With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments.Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

View Article: PubMed Central - PubMed

Affiliation: Department of Systems Ecology, Stockholm University, Stockholm, Sweden. francisco@ecology.su.se

ABSTRACT
Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0-3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods' incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.

Show MeSH