Invasions by exotic species represent both threats to ecosystems as well as opportunities to learn more about them. Among the invaders that will have the largest impacts are those that directly ...modify ecosystems and thus have cascading effects for resident biota. Exotics can affect ecosystems by altering system-level flows, availability, or quality of nutrients, food, and physical resources (e.g. living space, water, heat or light). The invader-mediated control of physical resources, typically achieved through the modification of habitats, has received limited attention in invasion biology. This reflects a general trend in ecology, and only recently has the concept of ecosystem engineering been developed to account for the role of species that shape habitats. Plants and animals in terrestrial and aquatic systems can both create and destroy structure. When introduced into ecosystems, these exotic engineers cause physical state changes with effects that ramify throughout the system. Although the consequences of these modifications are varied and complex, insight gained from general ecological principles offers an opportunity to predict what invaders will do upon their integration into systems. Examples from the literature suggest that introduced ecosystem engineers that increase habitat complexity or heterogeneity tend to cause abundances and/or species richness to rise, while those that decrease complexity tend to have the reverse effect. In assessing such patterns, however, it is critical to also consider spatial scales and the life habits of resident organisms. In addition to providing predictive power, recognition of engineering as a major means by which invasive species affect ecosystems provides a unifying theme for invasion biology and offers a chance to consider more fully the general role of species in ecosystems.
Ecosystem engineering in space and time Hastings, Alan; Byers, James E; Crooks, Jeffrey A ...
Ecology letters,
February 2007, Letnik:
10, Številka:
2
Journal Article
Recenzirano
The ecosystem engineering concept focuses on how organisms physically change the abiotic environment and how this feeds back to the biota. While the concept was formally introduced a little more than ...10 years ago, the underpinning of the concept can be traced back to more than a century to the early work of Darwin. The formal application of the idea is yielding new insights into the role of species in ecosystems and many other areas of basic and applied ecology. Here we focus on how temporal, spatial and organizational scales usefully inform the roles played by ecosystem engineers and their incorporation into broader ecological contexts. Two particular, distinguishing features of ecosystem engineers are that they affect the physical space in which other species live and their direct effects can last longer than the lifetime of the organism - engineering can in essence outlive the engineer. Together, these factors identify critical considerations that need to be included in models, experimental and observational work. The ecosystem engineering concept holds particular promise in the area of ecological applications, where influence over abiotic variables and their consequent effects on biotic communities may facilitate ecological restoration and counterbalance anthropogenic influences.
Small low-inflow intermittently closed estuaries are common in Mediterranean climates worldwide; however, despite their important contributions to ecosystem services and coastal resilience, their ...dynamics have been less well studied relative to classical (i.e., deeper, persistent freshwater inflow) estuaries. It is known that infragravity wave propagation into these estuaries can induce strong currents and that closures lead to stagnating flows and declining water quality; however, how the estuarine circulation (tidal and subtidal) dynamically drives and responds to these conditions remains largely unknown. Here we analyze over 4 years of hydrodynamic observations in Los Peñasquitos Lagoon, a low-inflow, intermittently closed estuary in Southern California, to examine wave propagation into the estuary, sill accretion, and the estuarine circulation response over tidal, fortnightly, seasonal, and interannual time scales, providing an unprecedented view as to how these systems respond to changing forcing. Wave observations near the estuary inlet show that wave energy inside the inlet, which contributes to sill accretion, is dependent on water level relative to the sill height and has a tidal variation due to wave-current interactions. Tidal phase averages of conditions during open, pre-closure, spring, neap, and closed conditions highlight the large dynamic range that these estuaries experience. During open, low sill conditions, circulation and stratification are consistent with stratification-induced periodic straining and subtidal exchange varies with the fortnightly cycle as observed in many classical estuaries. However, as the sill grows, tidal circulation weakens and becomes strongly sheared and the subtidal exchange no longer scales with a classical theoretical pressure-friction balance.
The impacts of changing climate regimes on emergent processes controlling the assembly of ecological communities remain poorly understood. Human alterations to the water cycle in the western United ...States have resulted in greater interannual variability and more frequent and severe extremes in freshwater flow. The specific mechanisms through which such extremes and climate regime shifts may alter ecological communities have rarely been demonstrated, and baseline information on current impacts of environmental variation is widely lacking for many habitats and communities. Here, we used observations and experiments to show that interannual variation in winter salinity levels in San Francisco Bay controls the mechanisms determining sessile invertebrate community composition during the following summer. We found consistent community changes in response to decadal‐scale dry and wet extremes during a 13‐year period, producing strikingly different communities. Our results match theoretical predictions of major shifts in species composition in response to environmental forcing up to a threshold, beyond which we observed mass mortality and wholesale replacement of the former community. These results provide a window into potential future community changes, with environmental forcing altering communities by shifting the relative influences of the mechanisms controlling species distributions and abundances. We place these results in the context of historical and projected future environmental variation in the San Francisco Bay Estuary.
Human alterations to the water cycle in the western United States have resulted in greater interannual variability and more frequent and severe freshwater flow extremes. We used observations and experiments to show that in San Francisco Bay, such interannual flow variation controls the mechanisms determining sessile invertebrate community composition. Dry and wet extremes during a 13‐year period produced strikingly different communities. These results provide a window into potential future community changes, with environmental forcing altering communities by shifting the relative influences of the mechanisms controlling species distributions and abundances.
The southern California coastline hosts low-inflow estuaries that have mouths that periodically close. Low-inflow estuaries can become hypoxic and are then often opened mechanically. The consequences ...of mouth closure and hypoxia (< 2 mg L
−1
O
2
) on macrobenthic densities, species richness, diversity, composition, and biological traits were evaluated for legacy data generated by the Pacific Estuarine Research Lab for Los Peñasquitos Lagoon (LPL) (1991–2006) and Tijuana Estuary (TJE) (1988–2004). LPL closed at least annually and TJE remained open during the study period. Effects were moderated by zone within the estuary (relative to the mouth) and season. Periodic closure in LPL was associated with raised macrofaunal density and diversity, especially at the mouth, and with suppressed seasonality. Closure favored soft-bodied (non-calcified) non-bioturbating, mobile, epifaunal taxa in LPL with planktotrophic development, large branchiae, and no vision. There were more spionid and capitellid polychaetes,
Traskorchestia traskiana
,
Cerithideopsis californica
,
Tagelus californianus
, and phoronids during closure. In contrast, hypoxia (< 2 mg L
−1
) measured during faunal sampling was associated with lower densities in LPL and different taxonomic composition, but no difference in taxon richness or diversity. There were more corophiid amphipods, small snails, tubificid oligochaetes,
Palaemon macrodactylus
(shrimp), and
Trichorixa reticulata
(insects) under hypoxic conditions, and retention of taxa with very large or small bodies and with vision. TJE densities were nearly double those of LPL; taxon richness and diversity (H’) were also higher in TJE. TJE hosted more burrowing, large-bodied, highly calcified taxa with planktotrophic development and no vision than LPL. Differences in composition and traits between the two estuaries disappeared in the middle and upper reaches, where ocean flushing was more limited. Historical long-term monitoring data for benthos, such as the data set analyzed here, offer a valuable baseline for evaluating ecosystem response to changes induced by climate, infrastructure development, contamination, or restoration.
A combination of historical bivalve surveys spanning 30-50 years and contemporary sampling were used to document the changes in bivalve community structure over time at four southern California and ...one northern Baja California estuaries. While there are limitations to the interpretation of historic data, we observed generally similar trends of reduced total bivalve species richness, losses of relatively large and/or deeper-dwelling natives, and gains of relatively small, surface dwelling introduced species across the southern California estuaries, despite fairly distinct bivalve communities. A nearly 50-year absence of bivalves from two wetlands surveyed in a Baja California estuary continued. A combination of site history and current characteristics (e.g., location, depth) likely contributes to maintenance of distinct communities, and both episodic and gradual environmental changes likely contribute to within-estuary temporal shifts (or absences). We highlight future research needed to determine mechanisms underlying patterns so that we can better predict responses of bivalve communities to future scenarios, including climate change and restoration.
The generality of ecological patterns depends inextricably on the scale at which they are examined. We investigated patterns of crab distribution and the relationship between crabs and vegetation in ...salt marshes at multiple scales. By using consistent monitoring protocols across 15 U.S. National Estuarine Research Reserves, we were able to synthesize patterns from the scale of quadrats to the entire marsh landscape to regional and national scales. Some generalities emerged across marshes from our overall models, and these are useful for informing broad coastal management policy. We found that crab burrow distribution within a marsh could be predicted by marsh elevation, distance to creek and soil compressibility. While these physical factors also affected marsh vegetation cover, we did not find a strong or consistent overall effect of crabs at a broad scale in our multivariate model, though regressions conducted separately for each site revealed that crab burrows were negatively correlated with vegetation cover at 4 out of 15 sites. This contrasts with recent smaller-scale studies and meta-analyses synthesizing such studies that detected strong negative effects of crabs on marshes, likely because we sampled across the entire marsh landscape, while targeted studies are typically limited to low-lying areas near creeks, where crab burrow densities are highest. Our results suggest that sea-level rise generally poses a bigger threat to marshes than crabs, but there will likely be interactions between these physical and biological factors. Beyond these generalities across marshes, we detected some regional differences in crab community composition, richness, and abundance. However, we found striking differences among sites within regions, and within sites, in terms of crab abundance and relationships to marsh integrity. Although generalities are broadly useful, our findings indicate that local managers cannot rely on data from other nearby systems, but rather need local information for developing salt marsh management strategies.
Although individual ecosystems vary greatly in the degree to which they have been invaded by exotic species, it has remained difficult to isolate mechanisms influencing invader success. One largely ...anecdotal observation is that polluted or degraded areas will accumulate more invaders than less-impacted sites. However, the role of abiotic factors alone in influencing invisibility has been difficult to isolate, often because the supply of potential invaders is confounded with conditions thought to increase vulnerability to invasion. Here, we conducted a field experiment to test how the assemblages of exotic versus native marine invertebrates changed during community assembly under different exposure levels of a common pollutant, copper. The experiment was conducted by deploying fouling panels in a Randomized Block Design in San Francisco Bay. Panels were periodically removed, placed into buckets with differing copper concentrations, and returned to the field after 3 days. This design allowed propagule availability to the plates to be statistically independent of short-term copper exposure. The results demonstrate that copper caused significant differences in community structure. Average native species richness was significantly affected by copper exposure, but average exotic richness was not. The total native species pool within treatments exhibited a greater than 40% decline within increasing copper, while the exotic species pool did not change significantly. These results confirm that anthropogenic alteration of abiotic factors influences invader success, indicating that management strategies to reduce invader impacts should include both efforts to improve environmental conditions as well as reduce invader supply.
Ecosystem engineers affect other organisms by creating, modifying, maintaining or destroying habitats. Despite widespread recognition of these often important effects, the ecosystem engineering ...concept has yet to be widely used in ecological applications. Here, we present a conceptual framework that shows how consideration of ecosystem engineers can be used to assess the likelihood of restoration of a system to a desired state, the type of changes necessary for successful restoration and how restoration efforts can be most effectively partitioned between direct human intervention and natural ecosystem engineers.
PDF
