Do PAHs Pose Unacceptable Ecological Risks to Terrestrial Receptors at Hazardous Waste Sites?

Polycyclic aromatic hydrocarbons (PAHs) are identified as Constituents of Potential Concern (CoPC) at many hazardous waste sites because of disposal, spills, leaking storage tanks, and incineration. The Superfund Public Information System (SPIS) RODs and CERCLIS Information database covering the period fiscal years 1996–1998 were queried for information on PAHs in soils. Forty-five sites were identified that had PAHs in soil. Predominantly, the sites were munitions facilities or military bases. Of the 45 sites, only two concluded that adverse ecological effects were occurring from PAHs. At both sites, the conclusions were based on Hazard Quotients (HQs) exceeding 1.0. For 29 sites, PAHs were characterized “as not posing an adverse effect” to plants or invertebrates. PAHs appeared not to pose an adverse effect at five other sites, but the information was equivocal. At another five sites, there “was too little information to evaluate possible PAH effects,” though PAHs did not figure in the remediation options. Empirical evidence indicates that wildlife exposures via food are mostly from foliar deposition, which tends to be low away from urban areas. To date, there is no evidence that PAHs in soils at hazardous waste sites result in adverse effects to plants, invertebrates, or wildlife.     

Grazing management influences the subsidy of terrestrial prey to trout in central Rocky Mountain streams (USA)

1. Research in forest and grassland ecosystems indicates that terrestrial invertebrates that fall into streams can be an important prey resource for fish, providing about 50% of their annual energy and having strong effects on growth and abundance. However, the indirect effects of land uses like cattle grazing on this important prey subsidy for stream salmonids are unclear. 2. During summer 2007, we compared the effects of three commonly used grazing systems on terrestrial invertebrate inputs to streams in northern Colorado and their use by trout. Cattle graze individual pastures for about 120 days under traditional season‐long grazing (SLG), about 35–45 days under simple rotational grazing and 10–20 days under intensive rotational grazing in this region. We also compared these effects to a fourth group of sites grazed only by wildlife (i.e. no livestock use). 3. Overall, rotational grazing management (either simple or intensive), resulted in more riparian vegetation, greater inputs of terrestrial invertebrates, greater biomass of terrestrial invertebrate prey in trout diets, a higher input compared to trout metabolic demand and more trout biomass than SLG. However, these differences were frequently not statistically significant owing to high variability, especially for trout diets and biomass. 4. Despite the inherent variability, riparian vegetation and terrestrial invertebrates entering streams and in trout diets at sites managed for rotational grazing were similar to sites managed for wildlife grazing only. 5. These results indicate that rotational grazing systems can be effective for maintaining levels of terrestrial invertebrate subsidies to streams necessary to support robust trout populations. However, factors influencing the effect of riparian grazing on stream subsidies are both spatially variable and complex, owing to differences in microclimate, invertebrate and plant populations and the efforts of ranchers to tailor grazing systems to specific riparian pastures.     

Nitrogen and phosphorus enrichment cause declines in invertebrate populations: a global meta-analysis

Human-driven changes in nitrogen (N) and phosphorus (P) inputs are modifying biogeochemical cycles and the trophic state of many habitats worldwide. These alterations are predicted to continue to increase, with the potential for a wide range of impacts on invertebrates, key players in ecosystem-level processes. Here, we present a meta-analysis of 1679 cases from 207 studies reporting the effects of N, P, and combined N + P enrichment on the abundance, biomass, and richness of aquatic and terrestrial invertebrates. Nitrogen and phosphorus additions decreased invertebrate abundance in terrestrial and aquatic ecosystems, with stronger impacts under combined N + P additions. Likewise, N and N + P additions had stronger negative impacts on the abundance of tropical than temperate invertebrates. Overall, the effects of nutrient enrichment did not differ significantly among major invertebrate taxonomic groups, suggesting that changes in biogeochemical cycles are a pervasive threat to invertebrate populations across ecosystems. The effects of N and P additions differed significantly among invertebrate trophic groups but N + P addition had a consistent negative effect on invertebrates. Nutrient additions had weaker or inconclusive impacts on invertebrate biomass and richness, possibly due to the low number of case studies for these community responses. Our findings suggest that N and P enrichment affect invertebrate community structure mainly by decreasing invertebrate abundance, and these effects are dependent on the habitat and trophic identity of the invertebrates. These results highlight the important effects of human-driven nutrient enrichment on ecological systems and suggest a potential driver for the global invertebrate decline documented in recent years.     

Woody debris and terrestrial invertebrates – effects on prey resources for brown trout (Salmo trutta) in a boreal stream

Intensive forestry and other activities that alter riparian vegetation may disrupt the connectivity and the flux of energy between terrestrial and aquatic habitats and have large effects on biota, especially in small streams. We manipulated the amount of in-stream wood and the flux of terrestrial invertebrate subsidies to determine how these factors affected potential food resources for drift-feeding brown trout (Salmo trutta ) in a boreal Swedish forest stream. Specifically, we followed the effects on the abundance of aquatic and terrestrial invertebrate fauna from June to August 2007. The treatments were 1) addition of wood, unmanipulated terrestrial invertebrate inputs, 2) reduction of terrestrial invertebrate inputs (using canopy covers), no addition of wood, 3) unmanipulated ambient conditions, 4) simultaneous addition of wood and reduction of terrestrial invertebrate inputs. Added wood resulted in greater biomass of aquatic invertebrate biomass, and both input and drift of terrestrial invertebrates were reduced by canopy covers. In terms of total potential prey biomass, the addition of wood with ambient levels of terrestrial invertebrate inputs had the highest standing crop of benthic, wood-living and terrestrial invertebrates combined, whereas the treatment with reduced terrestrial input and no wood added had the lowest standing crop. Our study indicates that forest practices that both reduce the recruitment of wood and the input of terrestrial invertebrates to small streams have negative effects on prey availability for drift-feeding brown trout. The positive effects of wood addition on biomass of aquatic macroinvertebrates may partly compensate for the negative effects of reduced terrestrial invertebrate subsidies.     

Importance of terrestrial subsidies for native brook trout in Appalachian intermittent streams

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What predicts the use by brook trout (Salvelinus fontinalis) of terrestrial invertebrate subsidies in headwater streams?

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Herbivory on Acacia seedlings in an East African savanna

Trees critically affect the functioning of savanna ecosystems through their effects on nutrient cycling, water availability, and patterns of space use by wildlife. Therefore, whatever factors influence successful recruitment of tree seedlings are important filters controlling savanna ecosystem function. In African savannas, large mammals have been considered the most important agents of mortality for adult trees, but their impacts on tree seedlings are not well‐known. Similarly, the effects of rodents and invertebrates as seedling predators are largely unstudied in Africa. To assess the relative roles of large mammals, rodents, and invertebrates as predators of Acacia seedlings in an African savanna, we conducted two experiments in which we exposed Acacia drepanolobium seedlings to different guilds of herbivores. In the first experiment, seedlings exposed to rodent and invertebrate herbivores did not suffer greater damage than did seedlings exposed only to invertebrates, suggesting that invertebrates caused most of the damage to the seedlings. In the second experiment, 63% of seedlings exposed to all herbivores (large mammals, rodents, and invertebrates) suffered major damage or mortality in 14 days. Seedlings exposed to only rodents and invertebrates, however, suffered damage at a faster rate than did seedlings exposed to rodents, invertebrates, and large mammals, suggesting that small herbivores (rodents and invertebrates) might be compensating for the removal of large herbivores. Certain specific types of damage, such as cotyledon removal, were significantly more common in areas from which large mammals had been excluded, suggesting that the invertebrate herbivore community may differ between areas with and without large mammals. Overall, invertebrates caused the greatest damage to seedlings while rodents had relatively little effect and no seedlings were consumed or trampled by large mammals. Our results indicate that invertebrates can have a pronounced influence on seedling survival for a dominant savanna tree, which in turn may influence tree recruitment and ecosystem function.     

Conservation of Southern Ocean Islands: invertebrates as exemplars

The Southern Ocean Islands (SOI) have an exceptionally high conservation status, and human activity on the islands is low by comparison with more tropical islands. In consequence, overexploitation, pollution and habitat destruction have had little influence on the invertebrate biotas of the islands, although overexploitation of pelagic species has the potential for an indirect influence via reduction of nutrient inputs to the terrestrial systems. By contrast, invasive alien species, the local effects of global climate change, and interactions between them are having large impacts on invertebrate populations and, as a consequence, on ecosystem functioning. Climate change is not only having direct impacts on indigenous invertebrates, but also seems to be promoting the ease of establishment of new alien invertebrate species. It is also contributing to population increases of invertebrate alien species already on the islands, sometimes with pronounced negative consequences for indigenous species and ecosystem functioning. Moreover, alien plants and mammals are also affecting indigenous invertebrate populations, often with climate change expected to exacerbate the impacts. Although the conservation requirements are reasonably well-understood for terrestrial systems, knowledge of freshwater and marine near-shore systems is inadequate. Nonetheless, what is known for terrestrial, freshwater and marine systems suggests that ongoing conservation of SOI invertebrates requires intervention from the highest political levels internationally, to slow climate change, to local improvements of quarantine measures to reduce the rates and impacts of biological invasions.     

Effect of riparian land use on contributions of terrestrial invertebrates to streams

Since terrestrial invertebrates are often consumed by stream fishes, land-use practices that influence the input of terrestrial invertebrates to streams are predicted to have consequences for fish production. We studied the effect of riparian land-use regime on terrestrial invertebrate inputs by estimating the biomass, abundance and taxonomic richness of terrestrial invertebrate drift from 15 streams draining catchments with three different riparian land-use regimes and vegetation types: intensive grazing — exotic pasture grasses (4 streams), extensive grazing — native tussock grasses (6 streams), reserve — native forest (5 streams). Terrestrial invertebrate drift was sampled from replicated stream reaches enclosed by two 1 mm mesh drift nets that spanned the entire channel. The mean biomass of terrestrial invertebrates that entered tussock grassland (12 mg ash-free dry mass m^–2 d^–1) and forest streams (6 mg AFDM m^–2 d^–1) was not significantly different (p > 0.05). However, biomass estimated for tussock grassland and forest streams was significantly higher than biomass that entered pasture streams (1 mg AFDM m^–2 d^–1). Mean abundance and richness of drifting terrestrial invertebrates was not significantly different among land-use types. Winged insects contributed more biomass than wingless invertebrates to both pasture and tussock grassland streams. Winged and wingless invertebrates contributed equally to biomass entering forest streams. Land use was a useful variable explaining landscape-level patterns of terrestrial invertebrate input for New Zealand streams. Evidence from this study suggests that riparian land-use regime will have important influences on the availability of terrestrial invertebrates to stream fishes.     

Aquatic and terrestrial invertebrate drift in southern Appalachian Mountain streams: implications for trout food resources

1. We characterised aquatic and terrestrial invertebrate drift in six south‐western North Carolina streams and their implications for trout production. Streams of this region typically have low standing stock and production of trout because of low benthic productivity. However, little is known about the contribution of terrestrial invertebrates entering drift, the factors that affect these inputs (including season, diel period and riparian cover type), or the energetic contribution of drift to trout. 2. Eight sites were sampled in streams with four riparian cover types. Drift samples were collected at sunrise, midday and sunset; and in spring, early summer, late summer and autumn. The importance of drift for trout production was assessed using literature estimates of annual benthic production in the southern Appalachians, ecotrophic coefficients and food conversion efficiencies. 3. Abundance and biomass of terrestrial invertebrate inputs and drifting aquatic larvae were typically highest in spring and early summer. Aquatic larval abundances were greater than terrestrial invertebrates during these seasons and terrestrial invertebrate biomass was greater than aquatic larval biomass in the autumn. Drift rates of aquatic larval abundance and biomass were greatest at sunset. Inputs of terrestrial invertebrate biomass were greater than aquatic larvae at midday. Terrestrial invertebrate abundances were highest in streams with open canopies and streams adjacent to pasture with limited forest canopy. 4. We estimate the combination of benthic invertebrate production and terrestrial invertebrate inputs can support 3.3–18.2 g (wet weight) m⁻² year⁻¹ of trout, which is generally lower than values considered productive [10.0–30.0 g (wet weight) m⁻² year⁻¹]. 5. Our results indicate terrestrial invertebrates can be an important energy source for trout in these streams, but trout production is still low. Any management activities that attempt to increase trout production should assess trout food resources and ensure their availability.     

Contribution of paddock trees to the conservation of terrestrial invertebrate biodiversity within grazed native pastures

Abstract: Paddock trees are a common feature in the agricultural landscapes of Australia. Recent studies have demonstrated the value of scattered paddock trees for soil fertility, native pasture plants and arboreal faunas; however, the degree to which scattered paddock trees contribute to the conservation of terrestrial invertebrate biodiversity within grazed landscapes remains unknown. We ask three questions: (i) Is there a difference between the terrestrial invertebrate assemblages found under paddock trees compared with surrounding grazed native pastures? (ii) Can gradients in soil and litter variables from the base of trees explain patterns in invertebrate assemblages? and (iii) Does the presence of scattered paddock trees have implications for the conservation of terrestrial invertebrate biodiversity within grazed native pastures? We used pitfall trapping and extraction from soil cores to sample the invertebrate assemblages under six New England Peppermint trees (Eucalyptus nova‐anglica Deane and Maiden) and compared them with assemblages sampled from the open paddock. Formicidae and Collembola univariate and multivariate data were analysed along with a range of soil and litter variables. We found (i) significant differences in the assemblages of invertebrates under trees compared with surrounding grazed pastures; (ii) that most soil and litter variables revealed gradients away from tree bases and these variables explained significant variation in invertebrate assemblages; and (iii) more native invertebrates and more species of invertebrates were found under trees compared with the surrounding pastures. We discuss the relationships between paddock trees, the ground and soil environments and the invertebrate communities that inhabit these environments, and conclude with a discussion of the future for paddock trees and the biota supported by them.     

Terrestrial wildlife responses to logging and fire in a Bolivian tropical humid forest

Logging and wildfire are significant anthropogenic disturbance agents in tropical forests. We compared the abundance and species richness of selected terrestrial wildlife taxa including small mammals, amphibians, reptiles, and terrestrial invertebrates in areas burned by wildfire and then logged and in adjacent undisturbed areas of a tropical humid forest in Bolivia. Disturbed areas had 24% less canopy cover than undisturbed areas but had 2.6 times the cover of large woody debris. Understory cover did not differ between disturbed and undisturbed areas. Small mammal abundance and species richness in disturbed areas were 43 and 70% higher, respectively, than in adjacent undisturbed areas. Herpetofaunal abundance did not differ significantly among disturbed and undisturbed areas, but trends for higher abundance were observed for both reptiles and amphibians in disturbed areas. Herpetofaunal species richness was significantly higher in disturbed compared to undisturbed areas. Total terrestrial invertebrate abundance, as estimated by pitfall traps, was significantly higher in undisturbed compared to disturbed areas mostly due to higher abundances of Formicidae and Blattidae. However, two invertebrate groups, Orthoptera and Lepidoptera (larvae) were more abundant in disturbed areas. Wildlife conservation strategies for areas where logging or wildfire occur should take into account species- or guild-specific responses to these disturbance agents.     

A critical analysis of the biological impacts of plasticizers on wildlife

This review provides a critical analysis of the biological effects of the most widely used plasticizers, including dibutyl phthalate, diethylhexyl phthalate, dimethyl phthalate, butyl benzyl phthalate and bisphenol A (BPA), on wildlife, with a focus on annelids (both aquatic and terrestrial), molluscs, crustaceans, insects, fish and amphibians. Moreover, the paper provides novel data on the biological effects of some of these plasticizers in invertebrates, fish and amphibians. Phthalates and BPA have been shown to affect reproduction in all studied animal groups, to impair development in crustaceans and amphibians and to induce genetic aberrations. Molluscs, crustaceans and amphibians appear to be especially sensitive to these compounds, and biological effects are observed at environmentally relevant exposures in the low ng l⁻¹ to µg l⁻¹ range. In contrast, most effects in fish (except for disturbance in spermatogenesis) occur at higher concentrations. Most plasticizers appear to act by interfering with the functioning of various hormone systems, but some phthalates have wider pathways of disruption. Effect concentrations of plasticizers in laboratory experiments coincide with measured environmental concentrations, and thus there is a very real potential for effects of these chemicals on some wildlife populations. The most striking gaps in our current knowledge on the impacts of plasticizers on wildlife are the lack of data for long-term exposures to environmentally relevant concentrations and their ecotoxicity when part of complex mixtures. Furthermore, the hazard of plasticizers has been investigated in annelids, molluscs and arthropods only, and given the sensitivity of some invertebrates, effects assessments are warranted in other invertebrate phyla.     

Montane refuges and topographic complexity generate and maintain invertebrate biodiversity: recurring themes across space and time

If a common set of landscape characteristics seem to predict spatial patterns of biodiversity in several regions with different biogeographic histories and community compositions, these could inform conservation. Two papers recently published in Journal of Insect Conservation provided evidence that topographic heterogeneity can play a major role in harbouring invertebrate community biodiversity, and that upland areas potentially function as refugia from infrequent but severe climatic conditions that occur over ecological timescales. Similar findings are being echoed in the growing body of phylogeographic literature on terrestrial invertebrates from montane landscape settings. The purpose of this short communication is to place the two recently published papers into a broader context. Phylogeographic studies usually focus on genetic diversity within and among populations, and at relatively deep evolutionary timescales. The parallels that appear to be emerging across different levels of biological organisation and temporal spectra suggest that (1) microevolutionary processes operating at the level of populations may ‘scale-up’ to macroevolutionary processes operating at the level of species or higher, and (2) certain landscape features—particularly topography—may be particularly important when formulating strategies to protect terrestrial invertebrate biodiversity.     

Enhanced invertebrate prey production following estuarine restoration supports foraging for multiple species of juvenile salmonids (Oncorhynchus spp.)

Estuaries provide crucial foraging resources and nursery habitat for threatened populations of anadromous salmon. As such, there has been a global undertaking to restore habitat and tidal processes in modified estuaries. The foraging capacity of these ecosystems to support various species of out‐migrating juvenile salmon can be quantified by monitoring benthic, terrestrial, and pelagic invertebrate prey communities. Here, we present notable trends in the availability of invertebrate prey at several sites within a restoring large river delta in Puget Sound, Washington, U.S.A. Three years after the system was returned to tidal influence, we observed substantial additions to amphipod, copepod, and cumacean abundances in newly accessible marsh channels (from 0 to roughly 5,000–75,000 individuals/m²). In the restoration area, terrestrial invertebrate colonization was dependent upon vegetative cover, with dipteran and hymenopteran biomass increasing 3‐fold between 1 and 3 years post‐restoration. While the overall biodiversity within the restoration area was lower than in the reference marsh, estimated biomass was comparable to or greater than that found within the other study sites. This additional prey biomass likely provided foraging benefits for juvenile Chinook, chum, and coho salmon. Primary physical drivers differed for benthic, terrestrial, and pelagic invertebrates, and these invertebrate communities are expected to respond differentially depending on organic matter exchange and vegetative colonization. Restoring estuaries may take decades to meet certain success criteria, but our study demonstrates rapid enhancements in foraging resources understood to be used for estuary‐dependent wildlife.     

The synergism between hydrocarbon pollutants and UV radiation: a potential link between coastal pollution and larval mortality

Coastal, benthic invertebrates with complex life history strategies are exposed to stage- and habitat-specific selective forces. In the coastal environment, benthic adults are exposed to polycyclic aromatic hydrocarbon pollutants (PAHs) due to their proximity to human activities (shipping, urbanization, and industrialization). Benthic invertebrates produce lipid-rich eggs or larvae that absorb PAHs from polluted estuaries and coastal waters. The larvae of many coastal invertebrates move offshore following release from benthic adults. During development in offshore waters, larvae of some species are exposed to relatively high levels of ultraviolet (UV) radiation. Marine organisms vary in their tolerance to PAHs and UV radiation. The purpose of this study was to examine the effects of the sequential exposure of the larvae of marine crabs to PAHs and UV radiation.Using laboratory experiments, the larvae of four crab species were exposed to PAHs and UV radiation. There was a significant synergistic effect of exposure to PAH (fluoranthene or pyrene) and UV radiation on larvae of the spider crab (Libinia dubia), the stone crab (Menippe adina) and the mud crab (Panopeus herbstii). Larvae of blue crabs (Callinectes sapidus) were exposed to PAHs and UV radiation in both laboratory and solar UV experiments. Significantly higher mortality occurred for C. sapidus larvae using either type of UV-artificial or solar.Larvae of coastal invertebrates with complex life history strategies are susceptible to the combined effects of PAHs and UV radiation. In this study, the exposure of crab larvae to PAHs and UV radiation resulted in mortality to crab larvae using laboratory and solar UV experiments. There were no effects on larval crab mortality due to PAH or UV radiation independently but mortality was as high as 100% when both factors were present.     

Responses of invertebrates to herbicide in Salix cinerea invaded wetlands: Restoration implications

The use of herbicides to control weeds, particularly large invasions, has now become an essential management tool in many ecological restoration projects. The herbicide glyphosate is routinely used to control the invasive weed, Grey Willow (Salix cinerea), within New Zealand wetlands. However, little is known about the effects of glyphosate on invertebrates. We determine the short‐term effects of glyphosate on the abundance and composition of the nontarget canopy invertebrate community in wetlands invaded by Grey Willow in New Zealand. Initially, the application of glyphosate and a surfactant showed no detectable effect on the canopy invertebrates examined in this study. However, 27 days after herbicide application, significant Grey Willow canopy loss caused dramatic decreases in the abundance of invertebrates in the glyphosate‐treated plots compared with the unsprayed plots. Invertebrates appeared to be sensitive to changes in vegetation structure, such as canopy loss. These results agree with previous studies that have shown that the negative impacts of glyphosate on invertebrate communities are related to indirect effects via habitat modification as the herbicide‐treated vegetation dies. From a terrestrial invertebrate perspective, this study suggests that the use of glyphosate herbicide is suitable for the control of invasive weeds within wetland restoration projects as it appears to have negligible impact on the canopy invertebrate assemblage.     

Risk Assessment as a Decision-Making Tool for Treatment of Emissions at a New Aluminum Smelter in Iceland: 3. Ecological Assessment

Predictive ecological risk assessment was used to determine whether any risk-reduction benefit would result from the installation and operation of wet scrubbers at an aluminum smelter in East Iceland. Sulfur dioxide and hydrogen fluoride exposure will not result in any appreciable risk to mosses, lichens, lodgepole pine, and heather/heath grassland communities beyond the dilution zone without scrubbers. With scrubbers, exceedances of plant criteria may occur beyond the dilution zone. Critical concentrations of polycyclic aromatic hydrocarbons (PAHs) and hydrogen fluoride (HF) in terrestrial wildlife food items were converted to critical air concentrations, which were then compared to modeled air concentrations. Terrestrial wildlife species are not expected to be exposed to PAH concentrations that result in appreciable risk. If wildlife species are assumed to consume only grasses, predicted HF exposures will not result in exceedance of toxicity thresholds. However, if wildlife species are assumed to consume only heather, thresholds are exceeded at some locations for the rock ptarmigan and wood mouse. Results of population modeling indicate no potential for population impacts to rock ptarmigan outside the facility boundary. Impacts to wood mouse carrying capacity are expected to extend beyond the dilution zone with scrubbers, but not without.     

Environmental Quality and Aquatic Invertebrate Metrics Relationships at Patagonian Wetlands Subjected to Livestock Grazing Pressures

Livestock grazing can compromise the biotic integrity and health of wetlands, especially in remotes areas like Patagonia, which provide habitat for several endemic terrestrial and aquatic species. Understanding the effects of these land use practices on invertebrate communities can help prevent the deterioration of wetlands and provide insights for restoration. In this contribution, we assessed the responses of 36 metrics based on the structural and functional attributes of invertebrates (130 taxa) at 30 Patagonian wetlands that were subject to different levels of livestock grazing intensity. These levels were categorized as low, medium and high based on eight features (livestock stock densities plus seven wetland measurements). Significant changes in environmental features were detected across the gradient of wetlands, mainly related to pH, conductivity, and nutrient values. Regardless of rainfall gradient, symptoms of eutrophication were remarkable at some highly disturbed sites. Seven invertebrate metrics consistently and accurately responded to livestock grazing on wetlands. All of them were negatively related to increased levels of grazing disturbance, with the number of insect families appearing as the most robust measure. A multivariate approach (RDA) revealed that invertebrate metrics were significantly affected by environmental variables related to water quality: in particular, pH, conductivity, dissolved oxygen, nutrient concentrations, and the richness and coverage of aquatic plants. Our results suggest that the seven aforementioned metrics could be used to assess ecological quality in the arid and semi-arid wetlands of Patagonia, helping to ensure the creation of protected areas and their associated ecological services.     

A new look at evolution in the Galápagos: evidence from the late Cenozoic marine molluscan fauna

Endemism is not as common in the marine invertebrate fauna of the Galápagos Islands region as in the adjacent terrestrial biota. Marine invertebrates in the Galápagos are largely cosmopolitan species from the Panamic, Indo-Pacific, Californian, or Peruvian faunal provinces. However, an endemic component is also present in the fauna. The observed pattern among marine invertebrate organisms can be accounted for by at least two processes: (1) genetic continuity between mainland and island populations mediated through planktonic larvae; and (2) lower rates of intrinsic evolutionary change. The evolutionary scenario standardly applied to terrestrial organisms in the Galápagos, namely, adaptive radiation and speciation in reproductive isolation from mainland source populations, does not apply to all marine invertebrates. Evidence in support of the alternative scenario for marine invertebrates comes from both published records of species occurring in the islands and recent studies of fossil-bearing deposits on several islands in the archipelago. Two misconceptions–considering the islands and sedimentary deposits to be older than now thought, and equating the rate of evolution of the terrestrial biota with the marine biota–can lead to an incorrect interpretation of evolution in the Galápagos Contrasts between marine invertebrate and terrestrial organisms serve to illustrate some fundamental differences which have important evolutionary implications. Some of these are: endemism; dispersal; taxonomic relationships; island definitions; rates of evolutionary change; and age of fossils. In terms of Darwin's evolutionary scenario, terrestrial organisms represent the paradigm and marine organisms represent the paradox.