Seasonal Abundance and Species Richness of Birds in Common Reed Habitats in Lake Erie

Abstract: Common reed (Phragmites australis) forms dense stands with deep layers of residual organic matter that negatively affects plant diversity and possibly habitat use by wetland birds. We sought to determine whether seasonal relative abundance and species richness of birds varied among 3 habitat types in Great Lakes coastal wetland complexes recently invaded by common reed. We used fixed-distance point counts to determine species relative abundances and species richness in edge and interior locales within common reed, cattail (Typha spp.), and meadow marsh habitats of various sizes during 2 summers (2001 and 2002) and 1 autumn (2001) at Long Point, Lake Erie, Ontario, Canada. We found that total relative abundance and species richness of birds were greater in common reed habitat compared to cattail or meadow marsh habitats. However, we also found that relative abundance of marsh-nesting birds was greater in meadow marsh habitat than in cattail and common reed during summer. Lastly, we found that, irrespective of habitat type, habitat edges had higher total relative abundance and species richness of birds than did habitat interiors. Our results show that common reed provides suitable habitat for a diversity of landbirds during summer and autumn but only limited habitat for many marsh-nesting birds during summer. Based on these results, we recommend restoration of meadow marsh habitat through reduction of common reed in Great Lakes wetlands where providing habitat for breeding marsh-nesting birds is an objective. Managers also might consider reducing the size of nonnative common reed stands to increase edge effect and use by birds, possibly including wetland birds.     

Habitat Use by Fishes in Coral Reefs,Seagrass Beds and Mangrove Habitats in the Philippines

Understanding the interconnectivity of organisms among different habitats is a key requirement for generating effective management plans in coastal ecosystems, particularly when determining component habitat structures in marine protected areas. To elucidate the patterns of habitat use by fishes among coral, seagrass, and mangrove habitats, and between natural and transplanted mangroves, visual censuses were conducted semiannually at two sites in the Philippines during September and March 2010–2012. In total, 265 species and 15,930 individuals were recorded. Species richness and abundance of fishes were significantly higher in coral reefs (234 species, 12,306 individuals) than in seagrass (38 species, 1,198 individuals) and mangrove (47 species, 2,426 individuals) habitats. Similarity tests revealed a highly significant difference among the three habitats. Fishes exhibited two different strategies for habitat use, inhabiting either a single (85.6% of recorded species) or several habitats (14.4%). Some fish that utilized multiple habitats, such as Lutjanus monostigma and Parupeneus barberinus, showed possible ontogenetic habitat shifts from mangroves and/or seagrass habitats to coral reefs. Moreover, over 20% of commercial fish species used multiple habitats, highlighting the importance of including different habitat types within marine protected areas to achieve efficient and effective resource management. Neither species richness nor abundance of fishes significantly differed between natural and transplanted mangroves. In addition, 14 fish species were recorded in a 20-year-old transplanted mangrove area, and over 90% of these species used multiple habitats, further demonstrating the key role of transplanted mangroves as a reef fish habitat in this region.     

Dumpsters and other anthropogenic structures as habitat for invasive African rock agama lizards in Florida

Invasive species often use habitat differently than native species and can benefit by occupying underutilized habitats during the invasion process. The Peter’s Rock Agama (Agama picticauda)—native to savannahs of sub-Saharan Africa—is successfully invading urban habitats in Florida, USA. During a field trip in urban southern Florida, we observed apparently high A. picticauda abundance around dumpsters used for human refuse, potentially because dumpsters provide refuge, thermoregulatory opportunities, abundant arthropod prey, and harbor few competitors. In this study, we surveyed abundance and built resource selection functions to better understand habitat use of A. picticauda in urban southern Florida. We tested whether hypothesized habitat features predictably influenced the abundance and occupancy of A. picticauda among sites and whether individuals used specific habitat features within sites. Across sites, we found A. picticauda abundance was positively correlated with the number of dumpsters, and, within sites, dumpsters were preferentially selected as habitat. Similarly, we also found two other anthropogenic structures, building crevices and electrical units, were positively selected habitats at population and individual scales. We hypothesize that dumpsters, crevices, and electrical units are selected resources because they are underutilized habitats by other species and they provide refuge, beneficial thermoregulatory opportunities, and in the case of dumpsters, foraging opportunities. Our study provides the first quantitative assessment of urban habitat use by non-native A. picticauda, and supports the importance of human structures as habitat. Our results suggest the intriguing possibility that the A. picticauda invasion in Florida may be exploiting a vacant niche in urban habitats during the invasion process.

     

Local Movement as a Measure of Habitat Quality in Stream Salmonids

Habitat assessments are often based on the premise that spatial variation in population density arises from, and accurately reflects, underlying differences in quality among habitats. Nonetheless, this premise has been criticized on both theoretical and empirical grounds. Habitat quality perhaps is best evaluated by examining behavioural processes which directly influence habitat use. We present an approach based on the assumption that measures of local movement, such as habitat-specific immigration and loss rates, provide useful indicators of habitat quality. A dynamic turnover model was used in conjunction with mark-recapture techniques to estimate movement parameters for brook charr, Salvelinus fontinalis, and Atlantic salmon, Salmo salar, in different stream habitats during the summer. Immigration and loss rates were derived from mark-recapture experiments covering short periods of time (6 days). Movement-based rankings of habitat quality for both charr (pools glides > riffles) and salmon (riffles > glides > pools) were in agreement with results from earlier studies. Over evaluation periods of up to 65 days, observed abundances were highly variable in time and fluctuated about the equilibrium abundances calculated from movement parameters in the short-term experiments, suggesting that movement-based parameters may be more stable than measures of abundance for evaluating salmonid habitat. Because the approach based on movement behaviour focuses on immigration and loss, two processes that directly generate density differentials between habitats, it provides a more reliable mechanistic basis for understanding habitat selection than do traditional approaches based on density–quality relationships.     

Density‐dependent habitat selection predicts fitness and abundance in a small lizard

Density‐dependent habitat selection has been used to predict and explain patterns of abundance of species between habitats. Thermal quality, a density‐independent component of habitat suitability, is often the most important factor for habitat selection in ectotherms which comprise the vast majority of animal species. Ectotherms may reach high densities such that individual fitness is reduced in a habitat due to increased competition for finite resources. Therefore, density and thermal quality may present conflicting information about which habitat will provide the highest fitness reward and ectotherm habitat selection may be density‐independent. Using ornate tree lizards Urosaurus ornatus at 10 sites each straddling two adjacent habitats (wash and upland), we tested the hypothesis that habitat selection is density‐dependent even when thermal quality differs between habitats. We first tested that fitness proxies decline with density in each habitat, indicating density‐dependent effects on habitat suitability. We also confirmed that the two habitats vary in suitability (quantified by food abundance and thermal quality). Next, we tested the predictions that habitat selection depends on density with isodar analyses and that fitness proxies are equal in the two habitats within a site. We found that monthly survival rates decreased with density, and that the wash habitat had more prey and higher thermal quality than the upland habitat. Lizards preferred the habitat with more food and higher thermal quality, lizard densities in the two habitats were positively correlated, and fitness proxies of lizards did not differ between habitats. These patterns are consistent with density‐dependent habitat selection, despite differences in thermal quality between habitats. We expect that density‐dependent habitat selection is widespread in terrestrial ectotherms when densities are high and temperatures are close to their optimal performance range. In areas where thermal quality is low, however, we expect that depletable resources, such as food, become less limiting because assimilating resources is more difficult.     

Assessing the quality of four inshore habitats used by post yolk‐sac Alosa sapidissima (Wilson 1811) in the Hudson River: a prelude to restoration

Habitat restoration within large rivers to enhance early life stages of fish is an emerging field. Prior to restoration, assessment of what constitutes “good” habitat is needed. We exemplify this with a study of larval Alosa sapidissima (American shad) in the Hudson River estuary in New York State, United States, which examines the quality of four main shallow water habitat types that have been reduced greatly by dredging activities. The larval stage has been identified as a sensitive period in need of mortality reduction. Habitats were examined as nursery habitat by comparing ambient conditions to known suitability indexes and by comparing relative abundance, loss rate, daily growth, and relative condition among habitats. Areas of lower velocity had greater abundances of shad ≤15.0 mm in length and shad growth was significantly higher. As shad became larger, those in areas of higher velocity had significantly higher relative condition, suggesting a shift in habitat use as larvae metamorphose into the juvenile stage. Contiguous backwater and secondary channel habitats had reduced loss rates during 2011 when there was high river discharge. No single habitat type examined in this study was found to be overall poor quality, and it is recommended that restoration sites be examined on an individual basis. More broadly, habitat diversity appears needed both for within‐year ontogeny as well as for longer‐term resiliency in the face of disturbance, such as storm‐driven high flows.     

Local species immigration,extinction, and turnover of butterflies in relation to habitat area and habitat isolation

Temporal dynamics of insect communities in terrestrial habitat fragments have been rarely studied. Here it was tested whether immigration, extinction, and turnover of butterfly species change with area and isolation of 31 calcareous grasslands. The area ranged from 0.03 to 5.14 ha, the isolation index from 2,100 to 86,000 (edge-to-edge distance 55–1,894 m). In both study years (1996, 2000), the total number of individuals (16,466, 15,101) and species (60, 54) sampled across all sites were similar and number of species increased with area in both years indicating an equilibrium. Rates of extinction (38% for habitat specialists vs. 20% for generalists) and turnover (51% vs. 35%) were higher, and rates of immigration (11% vs. 30%) were lower for habitat specialists than for generalists. Extinction and turnover rates decreased with increasing fragment size for both specialist (n =25 species) and generalist (n =36) butterflies, but specialists showed a significantly steeper decrease with increasing fragment size than generalists. Immigration rates increased with area. As a result, species number of habitat specialists declined in small habitats but not in large habitats between 1996 and 2000. No significant impact of habitat isolation on the butterfly community was found. The data suggest that large habitat fragments are of special importance for the conservation of the specialized, most endangered butterfly species. Habitat isolation appears to be less important, as butterflies can cope with the habitat mosaic in our study region.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Are urban habitats ecological traps for a native songbird? Season‐long productivity,apparent survival,and site fidelity in urban and rural habitats

The northern mockingbird Mimus polyglottos is a native species that is more abundant in urban than non‐urban habitats (i.e. an urban‐positive species). Abundance alone, however, is not an accurate index of habitat quality because urban habitats could represent ecological traps (attractive sink habitat) for urban‐positive species. We compared mockingbird nesting productivity, apparent survival, and decision rules governing site fidelity in urban and rural habitats. If the higher abundance of mockingbirds in urban habitats is driven by higher quality urban habitat, then we predicted that productivity of urban mockingbirds would exceed the estimated source‐sink threshold and productivity of non‐urban mockingbirds. If, on the other hand, urban habitats act as ecological traps, productivity would be lower in urban habitats and would fall below the estimated source‐sink threshold. Productivity of urban pairs exceeded that of non‐urban pairs and more than offset estimated adult mortality, which makes urban habitat a likely source habitat. Apparent adult survival was higher in urban habitats than in non‐urban habitats, although this could be driven by dispersal more than mortality. Decision rules also appeared to differ between urban and non‐urban populations. Females in urban habitats with successful nests were more likely to return than those with unsuccessful nests, whereas return rates of females in nonurban habitats were unrelated to nesting success and may be more related to nesting habitat availability. We conclude that urban habitats do not act as ecological traps that lure mockingbirds into sink habitat and that increased breeding productivity contributes to their success in urban habitats.     

Seasonal habitat selection by adult female polar bears in western Hudson Bay

Individual variation in habitat selection has emerged as an important component necessary for understanding population ecology. For threatened species, where habitat loss and alteration affect population trends, understanding habitat use provides insight into mechanisms of population change. Polar bears, Ursus maritimus, in the Western Hudson Bay subpopulation have experienced declines in body condition, survival, and abundance associated with delayed freeze-up and earlier break-up of sea ice due to climate change. Although this subpopulation has been intensively studied, sea ice habitat selection remains poorly understood. We developed a habitat selection model using a mixed conditional logistic regression to determine habitat selection across seasons (freeze-up, early winter, late winter, break-up) and assess individual variation in habitat selection. We used 8487 locations collected between 2004 and 2010 from 64 GPS satellite linked radio-collars on adult females to compare habitat selected to habitat available. Selection changed across seasons and varied the most among individuals during the freeze-up and break-up seasons. During later winter, there was less variation in habitat selection among individuals and bears showed the least amount of selection in habitat use. Distance to the denning area, a core terrestrial refuge habitat, was the top-ranked covariate in all seasons suggesting site fidelity plays a role in habitat selection. Some individual variation may have been due to reproductive status, though we could not account for this directly. Recognizing individual differences, especially in a rapidly changing environment, allows managers to identify critical habitats instead of simply average resources, and may lead to more successful efforts to protect habitats.     

Abundance and night-time habitat use patterns of Ponto-Caspian gobiid species (Pisces, Gobiidae) in the littoral zone of the River Danube, Hungary

We examined the abundance and meso‐habitat use of gobiid species during both day and night along 43 stretches (500‐m long) of the littoral zone at five locations of the Middle Danube, Hungary, in spring and in summer 2004. Electro‐fishing catch per unit effort sampling revealed significantly higher relative densities at night than during the day. Gobiids occupied all the available habitats encountered during sampling. Habitat‐abundance relationships from night‐time samples revealed that the two most abundant species, round goby Neogobius melanostomus and bighead goby Neogobius kessleri, were found in highest relative density along gravel beach and artificial rip‐rap habitats; these species were in relatively low density in sandy areas. Monkey goby Neogobius fluviatilis was more abundant in natural shorelines than in rip‐rap habitats and dispersed more consistently between sandy and gravel beaches. Tubenose goby Proterorhinus marmoratus demonstrated great plasticity in meso‐habitat use. In conclusion, Ponto‐Caspian gobies occurred rather consistently along the Hungarian section of the Danube, occupying all available habitats examined. Abundance‐habitat relations suggest plasticity in meso‐habitat use but partial segregation between species. Further studies are required at multiple spatial scales to assess how micro‐ and meso‐habitat use varies with fluctuating population densities.     

Effects of exotic <Emphasis Type="Italic">Spartina alterniflora</Emphasis> on the habitat patch associations of breeding saltmarsh birds at Chongming Dongtan in the Yangtze River estuary,China

Smooth cordgrass (Spartina alterniflora) is one of the most invasive exotic plants of saltmarshes worldwide. To understand the effects of smooth cordgrass invasion on the habitat use and selection by breeding saltmarsh birds, we compared species number and abundance of breeding birds in native reed (Phragmites australis) and smooth cordgrass-invaded habitats (reed-cordgrass mixed habitats and cordgrass monocultures) at Chongming Dongtan in the Yangtze River estuary, China. We further examined the similarity of bird communities in different habitats and habitat selection by dominant bird species. For saltmarsh generalists, species number and abundance did not differ among the habitats. For saltmarsh specialists, species number and abundance did not differ in reed monocultures and reed-cordgrass mixed habitats but were significantly lower in cordgrass monocultures than in reed monocultures and reed-cordgrass mixed habitats. ANOSIM indicated that the difference in bird communities was larger between cordgrass monocultures and the habitats with reed than between the habitats with reed. The saltmarsh specialists preferred reed monocultures, while saltmarsh generalists avoided reed monocultures. Most species indicated no selection (neither preferred nor avoided) on reed-cordgrass mixed habitats, and no species preferred the cordgrass monocultures. The use of cordgrass monocultures by the common saltmarsh birds was negatively related to their body size. This study suggests that the spread of exotic smooth cordgrass has greatly affected the species composition and structure of local bird communities and has been especially disadvantageous to the saltmarsh specialists.     

Establishment of Epiphytic Bromeliads in Successional Tropical Premontane Forests in Costa Rica

Plant community composition is the combined result of species-specific competitive abilities and the availability of propagules. For epiphytic plants, current hypotheses consider that dispersal-related factors are most important. By controlling seed dispersal constraints, we experimentally examined whether the community composition of epiphytic bromeliads in a tropical premontane area is determined during early phases of seedling recruitment. Also, we tested whether establishment success was related to eco-physiological traits of the species. A total of 7200 seeds were artificially affixed on several host trees in two secondary forest patches and in a mature forest stand. Four bromeliad species with differing physiological characteristics (CAM, C₃-CAM, and C₃) and habitat preference (secondary vs. primary forest) were selected. We found that differences in seed germination probability among habitats and species were not likely to influence community assembly. After 2 yr, seedling survival and plant development were relatively higher in the early-successional forest. Seedling establishment success was not associated with specific physiological and morphological adaptations or habitat preference of the studied species. Our results were not consistent with the described community composition and rates of population recruitment of the studied species in the same successional habitats. The results support the hypothesis that chance and historic events related to seed dispersal have an important influence on community assembly of epiphytic plants. In addition, differences in growth rates and reproductive turnover among species are expected to influence the relative abundance and recruitment rates in a particular habitat.     

The scale of resource specialization and the distribution and abundance of lycaenid butterflies

Numerous hypotheses have been proposed for the commonly observed, positive relationship between local abundance and geographic distribution in groups of closely related species. Here I consider how hostplant specialization and abundance affect the relative abundance and distribution of lycaenid butterflies (Lepidoptera: Lycaenidae). I first discuss three components of specialization: local specialization, turnover of specialization across a species’ range, and the minimum number of resources (or habitats) required by a species. Within this framework, I then consider one dimension of a lycaenid species’ niche, larval hostplant specialization. In a subalpine region of Colorado, I surveyed 11 lycaenid species and their hostplants at 17 sites. I compare this local information to continental hostplant use and large-scale distributions of the lycaenids and their hostplants. Local abundance of a lycaenid species is positively correlated with its local distribution (the number of sites occupied), but not with its regional or continental distribution. Neither local specialization (the number of hostplants used within one habitat) nor continental specialization (the number of hostplants used across many habitats) is correlated with local lycaenid abundance. Continental specialization is positively correlated with a species’ continental distribution, however. Finally, while generalist butterflies tend to have more hostplant available to them, differences in resource availability do not explain the differences in butterfly abundance. Although local abundance is correlated only with local distribution, I suggest that abundance-distribution relationships might emerge at regional and continental scales if local abundance were averaged across many habitat types. Consideration of the scale of a species’ resource specialization (within or among habitats) appears to be key to understanding the relationships between resource specialization, resource availability, and a species’ abundance and distribution. Received: 1 September 1999 / Accepted: 12 December 1999     

Habitat preferences,seasonal abundance and diets of rodents in Alage,Southern Ethiopia

To understand habitat preferences, seasonal abundance and diets of rodents in wet and dry season surveys were conducted in Alage, Southern Ethiopia. Sherman and snap traps were used to capture rodents from the four habitats: bushland, Acacia woodland, maize and wheat farmlands. A total of 3312 trap nights, from the four trapping habitats, yielded 776 individuals that represented 11 species of rodents. The distribution of rodents varied between habitats and seasons. Wet season rodent abundance was 52.3% while in the dry season it was 47.7%. Seasonal differences in species abundance were insignificant. Bushland habitat had high wet and dry season abundances with 137 and 211 individuals, respectively. Abundance was low in maize farm (57 individuals) in the wet season and wheat farm (10 individuals) in the dry season. Stomach content composition analysis of snap‐trapped rodents from different habitats showed differences between species and across seasons. Six rodent species were recorded as pests on the farmlands in this study area. In conclusion, variation in habitat preferences and diet of rodents in different habitats and across seasons might be due to the role of ground cover and food sources.     

Leaf-cutting ants negatively impact the regeneration of the Caatinga dry forest across abandoned pastures

The mechanisms affecting forest regeneration in human-modified landscapes are attracting increasing attention as tropical forests have been recognized as key habitats for biodiversity conservation, provision of ecosystem services, and human well-being. Here we investigate the effect of the leaf-cutting ants (LCA) Atta opaciceps on regenerating plant assemblages in Caatinga dry forest. Our study encompassed 15 Atta opaciceps colonies located in landscape patches with a gradient of forest cover from 8.7% to 87.8%, where we monitored regenerating individuals (seedlings and saplings of woody and herbaceous plants) in different habitats (nests, foraging areas, and control areas) over one year. We recorded 2,977 regenerating plant individuals, distributed among 55 species from 23 families. Herbaceous plants represented 82.1% and 58.2% of the total number of individuals and species, respectively. Species richness of both the whole and herbaceous plant assemblages increased along the forest cover gradient, but without difference between the habitats. Total plant abundance was highest in control areas followed by foraging areas and nests and this pattern held for both woody and herbaceous plants. Although forest cover did not influence the abundance of herbaceous plants and the whole plant assemblage, it positively affects woody plant abundance across control areas. Forest cover and habitat changed species composition of both the entire regenerating and the herbaceous assemblages. These results together indicate that LCA negatively impact regenerating plant assemblages, particularly in those sites with increased forest cover. As LCA proliferate in human-modified landscapes, they may prevent plant regeneration of disturbed areas.     

Habitat use by singing voles and tundra voles in the southern Yukon

Summary We investigated how far competitive interactions influence the use of habitats and relative abundance of two species of Microtus in the southwestern Yukon. We worked in the ecotone between alpine tundra and subalpine shrub tundra where populations of singing voles (Microtus miurus) and tundra voles (M. oeconomus) overlap little.We removed tundra voles from shrub tundra on one live-trapping area to look at the effect on the contiguous population of singing voles in alpine tundra. The removal of tundra voles did not affect the distribution or relative abundance of singing voles. The spatial distribution of these species and their movements within habitats suggest that they have a strong habitat preference.Populations of small mammals in the area are extremely dynamic and the relative importance of competitive interactions may change as density varies. At present we have no evidence that competition affects habitat use in M. miurus.     

Differential Habitat Use and Niche Partitioning by <Emphasis Type="Italic">Pseudomonas</Emphasis> Species in Human Homes

Many species of Pseudomonas have the ability to use a variety of resources and habitats, and as a result Pseudomonas are often characterized as having broad fundamental niches. We questioned whether actual habitat use by Pseudomonas species is equally broad. To do this, we sampled extensively to describe the biogeography of Pseudomonas within the human home, which presents a wide variety of habitats for microbes that live in close proximity to humans but are not part of the human flora, and for microbes that are opportunistic pathogens, such as Pseudomonas aeruginosa. From 960 samples taken in 20 homes, we obtained 163 Pseudomonas isolates. The most prevalent based on identification using the SepsiTest BLAST analysis of 16S rRNA () were Pseudomonas monteilii (42 isolates), Pseudomonas plecoglossicida, Pseudomonas fulva, and P. aeruginosa (approximately 25 each). Of these, all but P. fulva differed in recovery rates among evaluated habitat types (drains, soils, water, internal vertebrate sites, vertebrate skin, inanimate surfaces, and garbage/compost) and all four species also differed in recovery rates among subcategories of habitat types (e.g., types of soils or drains). We also found that at both levels of habitat resolution, each of these six most common species (the four above plus Pseudomonas putida and Pseudomonas oryzihabitans) were over- or under-represented in some habitats relative to their contributions to the total Pseudomonas collected across all habitats. This pattern is consistent with niche partitioning. These results suggest that, whereas Pseudomonas are often characterized as generalists with broad fundamental niches, these species in fact have more restricted realized niches. Furthermore, niche partitioning driven by competition among Pseudomonas species may be contributing to the observed variability in habitat use by Pseudomonas in this system.     

Lizard assemblages in the Vizcaino Biosphere Reserve, Mexico

Lizard assemblages were surveyed in eight selected habitats in the Vizcaino Biosphere Reserve in Baja California Sur, Mexico. We compared the species composition and relative abundance among habitats, considering habitat characteristics, such as vegetation type, vegetation ground coverage, and soil types. Thirteen lizard species were recorded. The most abundant species in almost all habitats was Uta stansburiana, accounting for 59% of all observations. Cnemidophorus tigris was the second most abundant species, accounting for 12% of all observations. The richest habitat was the rocky lower elevations of the Sierra de San Francisco (nine species). However, the habitat with the highest diversity value was Scammon's dunes. Implications of our findings for lizard conservation in this biosphere reserve are discussed.     

Processes regulating early post-settlement habitat use in a subtidal assemblage of brachyuran decapods

In highly mobile animals post-settlement dispersion of juveniles can strongly influence the observed patterns of abundance and distribution. To explore the relative importance of factors regulating the use of habitat by crabs we performed a multi-species manipulative experiment in a subtidal environment of the central Chilean coast. First, demographic patterns were established by performing a year-round crab survey in three discrete and well-known subtidal crab habitats: (1) algal turf, (2) cobbles and (3) shell hash. Second, habitat preferences were experimentally evaluated using concrete trays that were filled with different substrate types that simulate natural habitats. Settlement and recruitment rates were estimated from experimental trays that were left in the field and surveyed after 2 weeks (complete experiment was repeated 7 times throughout 1 year). Third, mortality, due to predation, was assessed by covering 50% of the trays with a 4-mm mesh-size screen that excluded large predators (i.e., fishes, shrimps). Fourth, habitat colonization rates were evaluated by quantifying the arrival, into open trays, of large juveniles (secondary dispersal). The most abundant species in this system (Paraxhantus barbiger, Cancer setosus, Taliepus dentatus and Pilumnoides perlatus) displayed clear habitat preferences at the time of settlement, evidenced by differences in density of recruits among habitats. Recruitment regulation by predation seemed to explain the observed patterns in only one case. For most species, however, evidence of ontogenetic change in the use of habitat, through active habitat redistribution by large juveniles, was detected. Thus, secondary dispersal among habitats seems to outweigh the influence of megalopae's habitat selection and post-settlement mortality as responsible for the observed demographic patterns.     

Low individual-level dietary plasticity in an island-invasive generalist forager

The ability of invasive mammals to adjust their diet in response to new or variable resources is often proposed to explain their invasion success on islands with differing environmental conditions, especially islands with strong spatiotemporal changes in the nature and abundance of their resources. In this study, we investigated how habitat heterogeneity and seasonal fluctuation in resource quality affect dietary breadth and plasticity in an island-invasive rodent, the black rat Rattus rattus, on a small Mediterranean island. We tested for dietary plasticity of rats at both the individual and population levels by using traditional dietary and stable isotope analyses at successively increasing time scales, coupled with a long-term study of individual rats in three habitats of close proximity. Dietary and movement analyses both indicated that R. rattus is able to exploit a wide range of resources and habitats. However, dietary plasticity and habitat breadth were far narrower at the individual level. Results revealed that rats exclusively used resources found in their local habitat, and very few individuals moved among adjacent habitats in pursuit of higher-quality resources, despite those resources being abundant in their immediate environment. This counterintuitive finding suggests that intraspecific interactions must restrict rat mobility. Our results suggest that even on small islands, accessibility of patchy and high-quality resources to individuals from the entire population is not systematic. This result has important implications when quantifying invasive rodent impacts on patchily distributed species, especially when studies use indirect methods such as dietary analyses as a substitute for direct observations of predatory behavior.