Limits...
Trophic diversity in two grassland ecosystems.

Pearson CV, Dyer LA - J. Insect Sci. (2006)

Bottom Line: The resulting trophic theory can be applied to understanding variation in insect diversity at different trophic levels.Path analysis revealed strong effects of herbivore diversity on diversity of other trophic levels.These results support hypotheses from other empirical studies, demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA. cpearso@tulane.edu

ABSTRACT
The roles of consumers (top-down forces) versus resources (bottom-up forces) as determinants of alpha diversity in a community are not well studied. Numerous community ecology models and empirical studies have provided a framework for understanding how density at various trophic levels responds to variation in the relative strength of top-down and bottom-up forces. The resulting trophic theory can be applied to understanding variation in insect diversity at different trophic levels. The objective of this research was to elucidate the strengths of direct and indirect interactions between plants and entire arthropod communities to determine the effects of trophic interactions on arthropod diversity. Grassland plant and insect diversity was measured in July 2001 to document patterns of diversity at multiple trophic levels. The study site includes riparian grasslands in North-Central Colorado on the Carpenter Ranch, owned and managed by The Nature Conservancy. This pastureland consists of sites with different management regimes: unmanaged pasture intermixed along riparian forest, and cattle grazed pasture with flood irrigation. Plant abundance and richness were higher on the grazed-irrigated pasture versus the unmanaged field. Path analysis revealed strong effects of herbivore diversity on diversity of other trophic levels. For the managed fields, top-down forces were important, with increases in enemy diversity depressing herbivore diversity, which in turn depressed plant abundance. For the unmanaged fields, bottom-up forces dominated, with increases in plant diversity causing increased herbivore diversity, which in turn increased enemy diversity. These results support hypotheses from other empirical studies, demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels.

Show MeSH

Related in: MedlinePlus

Path diagram based on analysis of data from unmanaged plots. Solid arrows indicate direct positive effects, solid lines with a circle-head indicate direct negative effects. Numbers next to effects are values of the significant path coefficients. Thickness of lines indicates relative effect size. The model statistically fit the data (X2 = 11.11, DF = 8, P = 0.1951).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2990313&req=5

i1536-2442-6-25-1-f04: Path diagram based on analysis of data from unmanaged plots. Solid arrows indicate direct positive effects, solid lines with a circle-head indicate direct negative effects. Numbers next to effects are values of the significant path coefficients. Thickness of lines indicates relative effect size. The model statistically fit the data (X2 = 11.11, DF = 8, P = 0.1951).

Mentions: Path analyses revealed strong effects of herbivore diversity on diversity of other trophic levels. For the managed fields (higher enemy diversity), our data supported the causal hypothesis that enemy diversity depressed herbivore diversity, which in turn depressed herbivore abundance, then plant abundance (Fig. 3). For the unmanaged fields (lower overall richness of plants and arthropods), the data supported the hypothesis that plant diversity caused increased herbivore diversity, which in turn increased enemy diversity (Fig. 4).


Trophic diversity in two grassland ecosystems.

Pearson CV, Dyer LA - J. Insect Sci. (2006)

Path diagram based on analysis of data from unmanaged plots. Solid arrows indicate direct positive effects, solid lines with a circle-head indicate direct negative effects. Numbers next to effects are values of the significant path coefficients. Thickness of lines indicates relative effect size. The model statistically fit the data (X2 = 11.11, DF = 8, P = 0.1951).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2990313&req=5

i1536-2442-6-25-1-f04: Path diagram based on analysis of data from unmanaged plots. Solid arrows indicate direct positive effects, solid lines with a circle-head indicate direct negative effects. Numbers next to effects are values of the significant path coefficients. Thickness of lines indicates relative effect size. The model statistically fit the data (X2 = 11.11, DF = 8, P = 0.1951).
Mentions: Path analyses revealed strong effects of herbivore diversity on diversity of other trophic levels. For the managed fields (higher enemy diversity), our data supported the causal hypothesis that enemy diversity depressed herbivore diversity, which in turn depressed herbivore abundance, then plant abundance (Fig. 3). For the unmanaged fields (lower overall richness of plants and arthropods), the data supported the hypothesis that plant diversity caused increased herbivore diversity, which in turn increased enemy diversity (Fig. 4).

Bottom Line: The resulting trophic theory can be applied to understanding variation in insect diversity at different trophic levels.Path analysis revealed strong effects of herbivore diversity on diversity of other trophic levels.These results support hypotheses from other empirical studies, demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA. cpearso@tulane.edu

ABSTRACT
The roles of consumers (top-down forces) versus resources (bottom-up forces) as determinants of alpha diversity in a community are not well studied. Numerous community ecology models and empirical studies have provided a framework for understanding how density at various trophic levels responds to variation in the relative strength of top-down and bottom-up forces. The resulting trophic theory can be applied to understanding variation in insect diversity at different trophic levels. The objective of this research was to elucidate the strengths of direct and indirect interactions between plants and entire arthropod communities to determine the effects of trophic interactions on arthropod diversity. Grassland plant and insect diversity was measured in July 2001 to document patterns of diversity at multiple trophic levels. The study site includes riparian grasslands in North-Central Colorado on the Carpenter Ranch, owned and managed by The Nature Conservancy. This pastureland consists of sites with different management regimes: unmanaged pasture intermixed along riparian forest, and cattle grazed pasture with flood irrigation. Plant abundance and richness were higher on the grazed-irrigated pasture versus the unmanaged field. Path analysis revealed strong effects of herbivore diversity on diversity of other trophic levels. For the managed fields, top-down forces were important, with increases in enemy diversity depressing herbivore diversity, which in turn depressed plant abundance. For the unmanaged fields, bottom-up forces dominated, with increases in plant diversity causing increased herbivore diversity, which in turn increased enemy diversity. These results support hypotheses from other empirical studies, demonstrating that changes in diversity of a single trophic level can cascade to effect diversity at other, nonadjacent trophic levels.

Show MeSH
Related in: MedlinePlus