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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.

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Shannon-Weiner Index (H’) (A), species richness (B), and abundance (C) for each trophic guild. Asterisks (*) indicate significant differences between management types (P1,79 < 0.0001). Grey bars = managed; black bars = unmanaged.
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i1536-2442-6-25-1-f02: Shannon-Weiner Index (H’) (A), species richness (B), and abundance (C) for each trophic guild. Asterisks (*) indicate significant differences between management types (P1,79 < 0.0001). Grey bars = managed; black bars = unmanaged.

Mentions: For both field types, the highest species richness was found in Hymenoptera, Diptera, Hemiptera, and Coleoptera, respectively. For the managed fields, the ranked order of dominance, based on abundance (not including Collembolans) was: Hemiptera, Thysanoptera, Diptera, Hymenoptera and Coleoptera, while for the unmanaged fields, the ranked order of dominance was: Thysanoptera, Hemiptera, Araneae, Hymenoptera and Diptera (Table 1). Managed fields had significantly higher plant abundance (F[1,79] = 50.3, P < 0.0001; r2 = 0.39) and richness (F[1,79] = 9.5, P = 0.003; r2 = 0.11) as well as overall arthropod abundance (F[1,79] = 25.0, P < 0.0001; r2 = 0.25) and richness (F[1,79] = 29.6, P < 0.0001; r2 = 0.28; Table 2 and 3). Managed fields were generally more diverse (except plant and herbivore diversity), had higher species richness and had greater abundance of all trophic groups, except predators (Fig 2) (spiders, the dominant predator, had very low abundance in managed fields). Overlap of shared species between managed versus unmanaged plot was low (Jaccard’s Similarity Index for all plots was 14.7 ± 0.47 SE, for unmanaged plots; 15.3 ± 0.67 SE, and managed plots; 21.0 ± .68 SE).


Trophic diversity in two grassland ecosystems.

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

Shannon-Weiner Index (H’) (A), species richness (B), and abundance (C) for each trophic guild. Asterisks (*) indicate significant differences between management types (P1,79 < 0.0001). Grey bars = managed; black bars = unmanaged.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

i1536-2442-6-25-1-f02: Shannon-Weiner Index (H’) (A), species richness (B), and abundance (C) for each trophic guild. Asterisks (*) indicate significant differences between management types (P1,79 < 0.0001). Grey bars = managed; black bars = unmanaged.
Mentions: For both field types, the highest species richness was found in Hymenoptera, Diptera, Hemiptera, and Coleoptera, respectively. For the managed fields, the ranked order of dominance, based on abundance (not including Collembolans) was: Hemiptera, Thysanoptera, Diptera, Hymenoptera and Coleoptera, while for the unmanaged fields, the ranked order of dominance was: Thysanoptera, Hemiptera, Araneae, Hymenoptera and Diptera (Table 1). Managed fields had significantly higher plant abundance (F[1,79] = 50.3, P < 0.0001; r2 = 0.39) and richness (F[1,79] = 9.5, P = 0.003; r2 = 0.11) as well as overall arthropod abundance (F[1,79] = 25.0, P < 0.0001; r2 = 0.25) and richness (F[1,79] = 29.6, P < 0.0001; r2 = 0.28; Table 2 and 3). Managed fields were generally more diverse (except plant and herbivore diversity), had higher species richness and had greater abundance of all trophic groups, except predators (Fig 2) (spiders, the dominant predator, had very low abundance in managed fields). Overlap of shared species between managed versus unmanaged plot was low (Jaccard’s Similarity Index for all plots was 14.7 ± 0.47 SE, for unmanaged plots; 15.3 ± 0.67 SE, and managed plots; 21.0 ± .68 SE).

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