Other Trophic Levels (other + trophic_level)

Distribution by Scientific Domains

Selected Abstracts

Top-down and bottom-up diversity cascades in detrital vs. living food webs

Lee A. Dyer
Abstract Apex predators and plant resources are both critical for maintaining diversity in biotic communities, but the indirect (,cascading') effects of top-down and bottom-up forces on diversity at different trophic levels are not well resolved in terrestrial systems. Manipulations of predators or resources can cause direct changes of diversity at one trophic level, which in turn can affect diversity at other trophic levels. The indirect diversity effects of resource and consumer variation should be strongest in aquatic systems, moderate in terrestrial systems, and weakest in decomposer food webs. We measured effects of top predators and plant resources on the diversity of endophytic animals in an understorey shrub Piper cenocladum (Piperaceae). Predators and resource availability had significant direct and indirect effects on the diversity of the endophytic animal community, but the effects were not interactive, nor were they consistent between living vs. detrital food webs. The addition of fourth trophic level beetle predators increased diversity of consumers supported by living plant tissue, whereas balanced plant resources (light and nutrients) increased the diversity of primary through tertiary consumers in the detrital resources food web. These results support the hypotheses that top-down and bottom-up diversity cascades occur in terrestrial systems, and that diversity is affected by different factors in living vs. detrital food webs. [source]

Climate change in the Arctic: using plant functional types in a meta-analysis of field experiments

C. F. Dormann
Summary 1,The effects of global climate change are predicted to be strongest in the Arctic. This, as well as the suitability of tundra as a simple model ecosystem, has led to many field experiments investigating consequences of simulated environmental change. 2,On the basis of 36 experiments reviewed here, minor light attenuation by clouds, small changes in precipitation, and increases in UV-B radiation and atmospheric CO2 concentrations will not affect arctic plants in the short term. However, temperature elevation, increases in nutrient availability and major decreases in light availability will cause an immediate plant-growth response and alter nutrient cycling, possibly creating positive feedbacks on plant biomass. The driver of future change in arctic vegetation is likely to be increased nutrient availability, arising for example from temperature-induced increases in mineralization. 3,Arctic plant species differ widely in their response to environmental manipulations. Classification into plant functional types proved largely unsatisfactory for generalization of responses and predictions of effects. 4,Nevertheless, a few generalizations and consistent differences between PFTs were detected. Responses to fertilization were the strongest, particularly in grasses. Shrubs and grasses were most responsive to elevated temperature. 5,Future studies should focus on interactive effects of environmental factors, investigate long-term responses to manipulations, and incorporate interactions with other trophic levels. With respect to plant functional types, a new approach is advocated, which groups species according to their responses to environmental manipulations. [source]

Mechanisms linking plant species richness to foraging of a large herbivore

Ling Wang
Summary 1.,There is general concern that local loss of plant diversity will adversely impact net primary productivity and other ecosystem properties. However, mechanisms linking plant diversity with other trophic levels, especially for large herbivores, are poorly understood. 2.,We examine the responses of foraging sheep to changes in plant species richness in an indoor cafeteria experiment involving six plant species richness levels (1, 2, 4, 6, 8 and 11 species) and three plant functional group compositions within each level, and in a field experiment involving three plant species richness levels (1, 4,6 or >8 species). 3.,Sheep preferred a diverse diet over a single diet even when palatable species were in the diet. Voluntary daily intake steadily rose with increases in plant species richness in both cafeteria and field experiments. The overall nutrient intake (i.e. daily energy and protein intakes) of sheep in the cafeteria also rose significantly with increased plant species richness until it reached a plateau at eight species. The quality of the diet selected by sheep was also significantly affected by plant species richness, but the variation of dietary quality was small and variable. 4.,High nutrient acquisition by the sheep depended on selecting those palatable species with high nutrient content from the plant forage on offer together with the complementary effects of plant species richness, especially for plant functional group richness. 5.,Synthesis and applications. Our experiments demonstrate an asymptotic relationship between plant species richness and voluntary intake by sheep. Increases in plant species richness from a low level led to increased daily nutrient intake, and presumably performance of the sheep. Natural grasslands are generally low in nutritional quality and so plant species richness will critically influence herbivore food intake and nutrition. The asymptotic relationship indicates that the maintenance of plant species richness in rangelands will benefit both domestic herbivore production and the conservation of biodiversity. [source]

Linking physiological traits to impacts on community structure and function: the role of root hemiparasitic Orobanchaceae (ex-Scrophulariaceae)

Summary 1The hemiparasitic Orobanchaceae (ex-Scrophulariaceae) are characterized by a distinctive suite of ecophysiological traits. These traits have important impacts on host plants and non-host plants, and influence interactions with other trophic levels. Ultimately, they can affect community structure and functioning. Here, we review these physiological traits and discuss their ecological consequences. 2The root hemiparasitic Orobanchaceae form a convenient subset of the parasitic angiosperms for study because: they are the most numerous and most widely distributed group of parasitic angiosperms; their physiological characteristics have been well studied; they are important in both agricultural and (semi)natural communities; and they are tractable as experimental organisms. 3Key traits include: high transpiration rates; competition with the host for nutrients and haustorial metabolism of host-derived solutes; uptake of host-derived secondary metabolites; dual autotrophic and heterotrophic carbon nutrition; distinct carbohydrate biochemistry; high nutrient concentrations in green leaf tissue and leaf litter; and small (often hairless and non-mycorrhizal) roots. 4Impacts on the host are detrimental, which can alter competitive balances between hosts and non-hosts and thus result in community change. Further impacts may result from effects on the abiotic environment, including soil water status, nutrient cycling and leaf/canopy temperatures. 5However, for non-host species and for organisms that interact with these (e.g. herbivores and pollinators) or for those that benefit from changes in the abiotic environment, the parasites may have an overall positive effect, suggesting that at the community level, hemiparasites may also be considered as mutualists. 6It is clear that through their distinctive suite of physiological traits hemiparasitic Orobanchaceae, have considerable impacts on community structure and function, can have both competitive and positive interactions with other plants, and can impact on other trophic levels. Many community level effects of parasitic plants can be considered analogous to those of other parasites, predators or herbivores. [source]

Disturbance frequency and functional identity mediate ecosystem processes in prairie streams

OIKOS, Issue 6 2009
Katie N. Bertrand
A major consequence of climate change will be the alteration of precipitation patterns and concomitant changes in the flood frequencies in streams. Species losses or introductions will accompany these changes, which necessitates understanding the interactions between altered disturbance regimes and consumer functional identity to predict dynamics of streams. We used experimental mesocosms and field enclosures to test the interactive effects of flood frequency and two fishes from distinct consumer groups (benthic grazers and water-column minnows) on recovery of stream ecosystem properties (algal form and biomass, invertebrate densities, metabolism and nutrient uptake rates). Our results generally suggest that periphyton communities under nutrient limitation are likely to recover more quickly when grazing and water-column minnows are present and these effects can diminish or reverse with time since the disturbance. We hypothesized that increased periphyton production and biomass was the result of increased nutrient turnover, but decreased light limitation and indirect effects on other trophic levels are alternative explanations. Recovery of stream ecosystem properties after a natural flood differed from mesocosms (e.g. lower algal biomass and no long algal filaments present) and species manipulations did not explain recovery of ecosystem properties; rather, ecosystem processes varied along a downstream gradient of increasing temperature and nutrient concentrations. Different results between field enclosures and experimental mesocosms are attributable to a number of factors including differences in algal and invertebrate communities in the natural stream and relatively short enclosure lengths (mean area=35.8 m2) compared with recirculating water in the experimental mesocosms. These differences may provide insight into conditions necessary to elicit a strong interaction between consumers and ecosystem properties. [source]