Foraging ecology, fluctuating food availability and energetics of wintering brent geese

Changing energy requirements and dramatic shifts in food availability are major factors driving behaviour and distribution of herbivores. We investigate this in wintering East Canadian High Arctic light-bellied brent geese Branta bernicla hrota in Northern Ireland. They followed a sequential pattern of habitat use, feeding on intertidal Zostera spp. in autumn and early winter before moving to predominantly saltmarsh and farmland in late winter and early spring. Night-time feeding occurred throughout and made a considerable contribution to the birds' daily energy budget, at times accounting for > 50% of energy intake. Nocturnal feeding, however, is limited to the intertidal, possibly because of predation risk on terrestrial habitat, and increases with moonlight. The amount of Zostera spp., declined dramatically after the arrival of birds, predominantly, but not entirely, due to consumption by the birds. Birds gained fat reserves in the first 2 months but then this was dramatically lost as their major food source collapsed and their daily energy intake declined. Single birds consistently fared worse than paired birds and pairs with juveniles fared better than those without suggesting a benefit of having a family to compete for food. Many birds leave the Lough at this time of reduced Zostera spp. for other sea inlets in Ireland but some remain. Body condition of the latter gradually improved in early spring and reflected a heavy reliance on terrestrial habitats, particularly farmland, to meet the birds' daily energy requirements. However, even in the period immediately before migration to the breeding ground, the birds did not regain the amount of abdominal fatness observed in November. The dramatic changes in available food and requirements of the birds drive the major changes seen in foraging behaviour as the birds evade starvation in the wintering period.

Direct and indirect effects of species displacements; an invading freshwater amphipod can disrupt leaf litter processing and shredder efficiency

Invasive species may threaten the fundamental role played by native macroinvertebrate shredders in determining energy flow and the trophic dynamics of freshwater ecosystems. Functionally, amphipods have long been regarded as mainly shredders, but they are increasingly recognized as major predators of other macroinvertebrate taxa. Furthermore, intraguild predation (IGP) between native and invasive amphipods underlies many species displacements. We used laboratory mesocosms to investigate what might happen to shredders and leaf-litter processing in water bodies invaded by the highly predatory Ponto-Caspian amphipod Dikerogammarus villosus, which is spreading rapidly throughout Europe and may soon invade the North American Great Lakes. The leaf-shredding efficiency of D. villosus was significantly lower than that of 3 Gammarus species (2 native and 1 invasive) that D. villosus has either already displaced or may be currently displacing in The Netherlands. In addition, D. villosus was a major predator of all of these native and invasive amphipod shredders and of a common isopod shredder Asellus aquaticus. Leaf processing in Gammarus and Asellus mesocosms declined rapidly in the presence of D. villosus and ceased altogether within 4 d because by then, all potential shredders had been killed and consumed. Furthermore, the shredding efficiency of surviving amphipods and isopods declined significantly within 2 d of the release of D. villosus, a result indicating that predator-avoidance behavior may override leaf processing. We discuss the implications of these direct and indirect effects of D. villosus invasions and species displacements on community structure and litter processing in aquatic ecosystems. © 2011 The North American Benthological Society.


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European hare (Lepus europaeus) invasion ecology: Implication for the conservation of the endemic Irish hare (Lepus timidus hibernicus)

European hare Lepus europaeus populations have undergone recent declines but the species has successfully naturalised in many countries outside its native range. It was introduced to Ireland during the mid-late nineteenth century for field sport and is now well established in Northern Ireland. The native Irish hare Lepus timidus hibernicus is an endemic subspecies of mountain hare L. timidus and has attracted major conservation concern following a long-term population decline during the twentieth century and is one of the highest priority species for conservation action in Ireland. Little is known about the European hare in Ireland or whether it poses a significant threat to the native mountain hare subspecies by compromising its ecological security or genetic integrity. We review the invasion ecology of the European hare and examine evidence for interspecific competition with the mountain hare for habitat space and food resources, interspecific hybridisation, disease and parasite transmission and possible impacts of climate change. We also examine the impact that introduced hares can have on native non-lagomorph species. We conclude that the European hare is an emerging and significant threat to the conservation status of the native Irish hare. Invasive mammal species have been successfully eradicated from Ireland before and immediate action is often the only opportunity for cost-effective eradication. An urgent call is issued for further research whilst the need for a European hare invasive Species Action Plan (iSAP) and Eradication strategy are discussed.

Rapid sympatric ecological differentiation of crater lake cichlid fishes within historic times

Background: After a volcano erupts, a lake may form in the cooled crater and become an isolated aquatic ecosystem. This makes fishes in crater lakes informative for understanding sympatric evolution and ecological diversification in barren environments. From a geological and limnological perspective, such research offers insight about the process of crater lake ecosystem establishment and speciation. In the present study we use genetic and coalescence approaches to infer the colonization history of Midas cichlid fishes (Amphilophus cf. citrinellus) that inhabit a very young crater lake in Nicaragua-the ca. 1800 year-old Lake Apoyeque. This lake holds two sympatric, endemic morphs of Midas cichlid: one with large, hypertrophied lips (~20% of the total population) and another with thin lips. Here we test the associated ecological, morphological and genetic diversification of these two morphs and their potential to represent incipient speciation.
Results: Gene coalescence analyses [11 microsatellite loci and mitochondrial DNA (mtDNA) sequences] suggest that crater lake Apoyeque was colonized in a single event from the large neighbouring great lake Managua only about 100 years ago. This founding in historic times is also reflected in the extremely low nuclear and mitochondrial genetic diversity in Apoyeque. We found that sympatric adult thin- and thick-lipped fishes occupy distinct ecological trophic niches. Diet, body shape, head width, pharyngeal jaw size and shape and stable isotope values all differ significantly between the two lip-morphs. The eco-morphological features pharyngeal jaw shape, body shape, stomach contents and stable isotopes (d15N) all show a bimodal distribution of traits, which is compatible with the expectations of an initial stage of ecological speciation under disruptive selection. Genetic differentiation between the thin- and thick-lipped population is weak at mtDNA sequence (FST = 0.018) and absent at nuclear microsatellite loci (FST < 0.001).
Conclusions: This study provides empirical evidence of eco-morphological differentiation occurring very quickly after the colonization of a new and vacant habitat. Exceptionally low levels of neutral genetic diversity and inference from coalescence indicates that the Midas cichlid population in Apoyeque is much younger (ca. 100 years or generations old) than the crater itself (ca. 1 800 years old). This suggests either that the crater remained empty for many hundreds of years after its formation or that remnant volcanic activity prevented the establishment of a stable fish population during the early life of the crater lake. Based on our findings of eco-morphological variation in the Apoyeque Midas cichlids, and known patterns of adaptation in Midas cichlids in general, we suggest that this population may be in a very early stage of speciation (incipient species), promoted by disruptive selection and ecological diversification.

delta C-13 and delta N-15 reveal significant differences in the coastal foodwebs of the seas surrounding Trinidad and Tobago

This study assessed nearshore, marine ecosystem function around Trinidad and Tobago (TT). The coastline of TT is highly complex, bordered by the Atlantic Ocean, the Caribbean Sea, the Gulf of Paria and the Columbus Channel, and subject to local terrestrial runoff and regional riverine inputs (e.g. the Orinoco and Amazon rivers). Coastal organisms can assimilate energy from allochthonous and autochthonous Sources, We assessed whether stable isotopes delta C-13 and delta N-15 Could be used to provide a rapid assessment of trophic interactions in primary consumers around the islands. Filter-feeding (bivalves and barnacles) and grazing organisms (gastropods and chitons) were collected from 40 marine sites during the wet season. The flesh of organisms was analysed for delta C-13 and delta N-15. Results indicate significant variation in primary consumers (by feeding guild and sampling zone). This variation was linked to different energy Sources being assimilated by consumers. Results suggest that offshore production is fuelling intertidal foodwebs; for example, a depleted delta C-13 signature in grazers from the Gulf of Paria, Columbus Channel and the Caribbean and Atlantic coastline of 9 Tobago indicates that carbon with an offshore origin (e.g. phytoplankton and dissolved organic matter) is more important than benthic or littoral algae (luring the wet season. Results also confirm findings from other studies indicating that much of the coastline is subject to Cultural eutrophication. This Study revealed that ecosystem function is spatially variable around the coastline of TT, This has clear implications for marine resource management, as a single management approach is unlikely to be successful at a national level.

Biodiversity loss and ecosystem functioning: Distinguishing between number and identity of species

Given currently high rates of extinction, it is critical to be able to predict how ecosystems will respond to loss of species and consequent changes in community structure. Much previous research in this area has been based on terrestrial systems, using synthetically assembled communities. There has beer! much less research on inter-trophic effects in different systems, using in situ removal experiments. Problems with the design of early experiments have made it difficult to determine whether reductions in ecosystem functioning in low diversity treatments were due to the number of species present or merely to the reduced likelihood of including particular (

Simulated predator extinctions: Predator identity affects survival and recruitment of oysters

The rate of species loss is increasing at a global scale, and human-induced extinctions are biased toward predator species. We examined the effects of predator extinctions on a foundation species, the eastern oyster (Crassostrea virginica). We performed a factorial experiment manipulating the presence and abundance of three of the most common predatory crabs, the blue crab (Callinectes sapidus), stone crab (Menippe mercenaria), and mud crab (Panopeus herbstii) in estuaries in the eastern United States. We tested the effects of species richness and identity of predators on juvenile oyster survival, oyster recruitment, and organic matter content of sediment. We also manipulated the density of each of the predators and controlled for the loss of biomass of species by maintaining a constant mass of predators in one set of treatments and simultaneously using an additive design. This design allowed us to test the density dependence of our results and test for functional compensation by other species. The identity of predator species, but not richness, affected oyster populations. The loss of blue crabs, alone or in combination with either of the other species, affected the survival rate of juvenile oysters. Blue crabs and stone crabs both affected oyster recruitment and sediment organic matter negatively. Mud crabs at higher than ambient densities, however, could fulfill some of the functions of blue and stone crabs, suggesting a level of ecological redundancy. Importantly, the strong effects of blue crabs in all processes measured no longer occurred when individuals were present at higher-than-ambient densities. Their role as dominant predator is, therefore, dependent on their density within the system and the density of other species within their guild (e.g., mud crabs). Our findings support the hypothesis that the effects of species loss at higher trophic levels are determined by predator identity and are subject to complex intraguild interactions that are largely density dependent. Understanding the role of biodiversity in ecosystem functioning or addressing practical concerns, such as loss of predators owing to overharvesting, remains complicated because accurate predictions require detailed knowledge of the system and should be drawn from sound experimental evidence, not based on observations or generalized models.