Habitat complexity: approaches and future directions

Population and ecosystem approaches in ecology -- The maintenance and functional consequences of species diversity -- Biodiversity and ecosystem functioning -- Food webs, interaction webs, and ecosystem functioning -- Stability and complexity of ecosystems: new perspectives on an old debate -- Material cycling and the overall functioning of ecosystems -- Spatial dynamics of biodiversity and ecosystem functioning: metacommunities and meta-ecosystems -- Evolution of ecosystems and ecosystem properties -- Postface: toward an integrated, predictive ecology.

Using functional responses to quantify notonectid predatory impacts across increasingly complex environments

Relationships between functional diversity and ecosystem functioning: A review

Species diversity is important to ecosystems because of the increased probability of including species that are strong interactors and/or because multiple-species communities are more efficient at using resources due to synergisms and resource partitioning. Genetic diversity also contributes to ecosystem function through effects on primary productivity, community structure and resilience, and modulating energy and nutrient fluxes. Lacking are studies investigating the relationship between ecosystem function and diversity where hierarchical levels of biological diversity are systematically varied during experimentation. In this experiment, we manipulated both species and genotypic diversity of two Daphnia species in microcosms initially seeded with Chlamydomonas and measured community- and ecosystem-level properties to determine which level of diversity was most important for explaining variation in the property. Our results show that species diversity alters bacterial community composition while high genotypic diversity reduces bacterial richness and primary productivity. In addition, the highest levels of genotypic and species richness appear to increase community and ecosystem stability. These findings reveal that species and genotypic diversity are significant drivers of community and ecosystem properties and stability.

Theoretical studies of the relationship between ecosystem complexity and stability usually conclude that systems with more species, more interspecific interactions per species (connectance), or stronger interactions are not as likely to be stable as systems with fewer of these attributes (Gardner and Ashby 1970; May 1972, 1974, 1979; DeAngelis 1975; Gilpin 1975; Pimm 1979a, 1979b, 1980). Yet, in one of the few empirical investigations of this problem, McNaughton (1977) concluded that increased complexity stabilized certain ecosystem properties; more precisely, that a large mammalian grazer changed total green plant biomass less in more diverse than in less diverse grassland plots. We try to resolve this apparent contradiction between theory and empiricism by investigating, in model grazing systems, the relationship between complexity and the lack of change in plant biomass (which we call biomass stability) following the removal of an herbivore. We established a set of structured food web models composed of one herbivore and n plant species. The models were based on the familiar Lotka-Volterra equations, and we selected their parameters over intervals designed to be biologically sensible and also to reflect the pattern of interactions in the food web. Only those models with a locally stable equilibrium involving species with positive biomasses were retained for further analysis. From each model of this subset, the herbivore was removed and the resultant change in total plant biomass followed until a new stable equilibrium was achieved. Relative biomass stability was calculated from the relative change in the total plant biomasses of the two equilibria. Clearly, a ratio near unity indicates biomass stability, while a large ratio indicates that biomass has increased considerably, following removal of the herbivore. We modeled webs of varying complexity as measured by: (1) the number of species; (2) the number of competitive interactions between plant species; and (3) species diversity (a measure combining the number of species and their relative abundances), and related these features to biomass stability. Our conclusion is that increased complexity can enhance biomass stability, even

With the rapid accumulation of plant trait data, major opportunities have arisen for the integration of these data into predicting ecosystem primary productivity across a range of spatial extents. Traditionally, traits have been used to explain physiological productivity at cell, organ, or plant scales, but scaling up to the ecosystem scale has remained challenging. Here, we show the need to combine measures of community-level traits and environmental factors to predict ecosystem productivity at landscape or biogeographic scales. We show how theory can extend the production ecology equation to enormous potential for integrating traits into ecological models that estimate productivity-related ecosystem functions across ecological scales and to anticipate the response of terrestrial ecosystems to global change.

Using network ecology to understand and mitigate long‐term insect declines

Abstract. Structural complexity in ecosystems creates an assortment of microhabitat types and has been shown to support greater diversity and abundance of associated organisms. The 3D structure of an environment also directly affects important ecological parameters such as habitat provisioning and light availability and can therefore strongly influence ecosystem function. Coral reefs are architecturally complex 3D habitats, whose structure is intrinsically linked to the ecosystem biodiversity, productivity, and function. The field of coral ecology has, however, been primarily limited to using 2-dimensional (2D) planar survey techniques for studying the physical structure of reefs. This conventional approach fails to capture or quantify the intricate structural complexity of corals that influences habitat facilitation and biodiversity. A 3-dimensional (3D) approach can obtain accurate measurements of architectural complexity, topography, rugosity, volume, and other structural characteristics that affect biodiversity and abundance of reef organisms. Structurefrom- Motion (SfM) photogrammetry is an emerging computer vision technology that provides a simple and cost-effective method for 3D reconstruction of natural environments. SfM has been used in several studies to investigate the relationship between habitat complexity and ecological processes in coral reef ecosystems. This study compared two commercial SfM software packages, Agisoft Photoscan Pro and Pix4Dmapper Pro 3.1, in order to assess the cpaability and spatial accuracy of these programs for conducting 3D modeling of coral reef habitats at three spatial scales.

Prey refuges are an important mechanism by which habitat structure affects ecological communities. In freshwater fish communities, most research has focused on aquatic vegetation and neglected alternative habitats. We explored the interactions between predator foraging modes of two common littoral piscivores (Muskellunge Esox masquinongy and Largemouth Bass Micropterus salmoides), and antipredator behaviors of two common prey species (Golden Shiner Notemigonus crysoleucas and Bluegill Lepomis macrochirus) across a gradient of coarse woody habitat (CWH) complexity in a mesocosm setting. We hypothesized that experiments employing a generalist predator (Largemouth Bass) and behaviorally flexible prey (Bluegills) would show a stronger refuging effect of CWH than would a less gbehaviorally flexible prey (Golden Shiners) and an obligate ambush predator (Muskellunge). Predator–prey interactions were observed in laboratory pools containing coniferous deadfalls. A refuging effect of coarse wood was not supported under our experimental conditions. Golden Shiners experienced an increase in mortality rate with increasing coarse wood complexity when preyed upon by Largemouth Bass. Both prey species reduced activity rates with increasing CWH complexity when preyed upon by Largemouth Bass but exhibited different response patterns for changes in shoal size, number of isolated individuals, and proximity to predators, which may explain differences in vulnerability across the habitat gradient. Increasing CWH complexity was associated with changes in Largemouth Bass behaviors, including reductions in activity rates and reduced capture efficiency at intermediate complexities, but the changes depended on the prey species. Habitat complexity did not strongly affect foraging success or behavior of Muskellunge. Our results reinforce the importance of species‐specific behavioral traits in determining influences of physical habitat on predator–prey relationships in freshwater fish communities.

Effects of Subordinate Plant Species in Plant and Soil Community Structure and Ecosystem Functioning

We evaluate the empirical and theoretical support for the hypothesis that a large proportion of native species richness is required to maximize ecosystem stability and sustain function. This assessment is important for conservation strategies because sustenance of ecosystem functions has been used as an argument for the conservation of species. If ecosystem functions are sustained at relatively low species richness, then arguing for the conservation of ecosystem function, no matter how important in its own right, does not strongly argue for the conservation of species. Additionally, for this to be a strong conservation argument the link between species diversity and ecosystem functions of value to the human community must be clear. We review the empirical literature to quantify the support for two hypotheses: (1) species richness is positively correlated with ecosystem function, and (2) ecosystem functions do not saturate at low species richness relative to the observed or experimental diversity. Few empirical studies demonstrate improved function at high levels of species richness. Second, we analyze recent theoretical models in order to estimate the level of species richness required to maintain ecosystem function. Again we find that, within a single trophic level, most mathematical models predict saturation of ecosystem function at a low proportion of local species richness. We also analyze a theoretical model linking species number to ecosystem stability. This model predicts that species richness beyond the first few species does not typically increase ecosystem stability. One reason that high species richness may not contribute significantly to function or stability is that most communities are characterized by strong dominance such that a few species provide the vast majority of the community biomass. Rapid turnover of species may rescue the concept that diversity leads to maximum function and stability. The role of turnover in ecosystem function and stability has not been investigated. Despite the recent rush to embrace the linkage between biodiversity and ecosystem function, we find little support for the hypothesis that there is a strong dependence of ecosystem function on the full complement of diversity within sites. Given this observation, the conservation community should take a cautious view of endorsing this linkage as a model to promote conservation goals.

We examined the role of habitat complexity in influencing predator–prey interactions between fish and tadpoles. Tadpoles of the Squirrel Treefrog (Hyla squirella) and the Eastern Narrow-Mouth Toad (Gastrophryne carolinensis) were exposed to Eastern Mosquitofish (Gambusia holbrooki) under different degrees of habitat complexity (no cover, low cover, and high cover) in a randomized block, replicated, controlled experiment using wading pools. This study indicates that Gambusia can quickly and dramatically impact tadpole populations even at low predator densities and can forage effectively in vegetated areas that might normally serve as prey refugia from larger predatory fish (e.g., Lepomis spp.). Moreover, the influence of habitat complexity on predator-prey interactions may be species-specific. The number of H. squirella tadpoles consumed was not affected significantly by the degree of habitat complexity; however, consumption of G. carolinensis by Gambusia decreased with increasing habitat complexity. We attribute this finding to the observation that G. carolinensis are less active than H. squirella and, therefore, more difficult for Gambusia to detect with increasing habitat complexity.

Habitat complexity, dispersal and metapopulations: Macroscopic study of a predator–prey system

In this paper, the effects of aquatic vegetation on fish species interactions has been reviewed. Predator-prey interaction between largemouth bass (LMB) (Micropterus salmoides) and bluegill (BLG) (Lepomis macrochirus) has been as an excellent example of understanding the effects of aquatic vegetation on the predator-prey interactions. So the focus has been given on the interactions between those species in order to evaluate a general pattern of aquatic vegetation effects on predator-prey interactions of most fish species. Predatory success of largemouth bass on bluegill can vary with complex habitat, predator and prey body size. Complex habitat affects bluegill distribution and largemouth bass predatory' success. Bluegill can avoid predation risk by hiding itself in complex habitat. Most of the authors agreed that largemouth bass predatory success declined as habitat complexity increased. Thus it can be concluded that aquatic vegetation should be kept an intermediate density so that both interacting species can benefit.

A test of the subsidy–stability hypothesis: the effects of terrestrial carbon in aquatic ecosystems