Habitat Separation Research Articles

Shifting mosaic in maintaining diversity of floodplain tree species in the northern temperate zone of Japan

We examined the relationships between floodplain forest structure and disturbance frequencies in bar-braided and incised-meandering channel sections of the Rekifune River, northern Japan. This was undertaken with special reference to the life history traits at seedling and reproductively mature stages of eight dominant species ( Chosenia arbutifolia, Populus maximowiczii, Toisusu urbaniana, Salix sachalinensis, Salix pet-susu, Alnus hirsuta, Ulmus japonica, and Fraxinus mandshurica var. japonica). These species were generally arranged along the flood frequency and intensity gradient represented by five geomorphic surface types: gravel bar, lower and upper floodplain, secondary channel, and terrace. However, habitat separation between seedlings and conspecific mature stands occurred with geomorphic surface type in four of the eight species, suggesting that these species require more than one geomorphic surface type to complete their life cycles. Comparisons of stand-replacement disturbances between the bar-braided and incised-meandering rivers suggested that the shifting mosaic pattern in association with the evolution of land surfaces plays a vital role in maintaining variety in regeneration habitats and development of riparian forests in a half-century time scale. We conclude that the key factors maintaining the diversity of floodplain tree species in the studied northern temperate forests are: (1) the development of diverse geomorphic surfaces providing regeneration and habitat niches, and (2) the timing of maturation and lifespan of early and mid-successional species consistent with the disturbance frequency.

Fish assemblage patterns in the littoral zone of a European reservoir

Summary1. Although reservoirs are common aquatic habitats in Europe, there is little quantitative information on the spatial organisation of fish assemblages inhabiting their littoral zones. Consequently, we characterised fish assemblage structure in the littoral zone of a reservoir (Lake Pareloup) in SW France during late spring, summer and early autumn (the growing season).2. We measured the relative abundance of fish weekly, from mid‐May to mid‐October, using point abundance sampling by electrofishing. We identified temporal patterns in assemblage structure using hierarchical cluster analysis, and then characterised the spatial distribution of 17 defined ecospecies using a Kohonen self‐organising map (SOM, an unsupervised Artificial Neural Network).3. Our analyses revealed three distinct faunal structures within the littoral zone. From mid‐May to mid‐July, adults and young‐of‐the‐year (0+) occupied separate habitats, with most 0+ fish in vegetated habitats and adults in open water. From mid‐July to late August, some 0+ co‐occurred with adults, but most 0+ fishes remained in vegetated areas. Finally, from late August to mid‐October, most fish (both 0+ and adults) left the vegetation for unvegetated littoral habitats, the exception being fish species known to be dependent on macrophytes.4. Contrary to patterns for adult fishes, the 0+ fish assemblage was dynamic. These dynamics were driven by ontogenetic species‐specific habitat changes. Consequently, there was little evidence of stable assemblages or strong assemblage–habitat relationships that would be expected of an ‘interactive’ assemblage. It is likely that the patterns observed are a result of species‐specific response to habitat availability in the lake.

Dietary Analysis of Sympatric Arctic Char and Brown Trout in Lough Muckross, South-Western Ireland

Stable isotope analysis was used to examine dietary separation between sympatric Arctic char (Salvelinus alpinus (L.)) and brown trout (Salmo trutta) in Lough Muckross, Co. Kerry, and to test the applicability of the interactive segregation hypothesis to observed trophic relationships. Gut contents showed both species fed seasonally on similar prey. Stable isotopes indicated the long-term nature of the similarity in feeding relationships, with results providing no support for the interactive segregation hypothesis as used to explain dietary differences between the species in Scandinavian lakes. Feeding and capture patterns indicative of differences in habitat use were consistent with the MacArthur niche compression hypothesis, with differences in temperature preferences for both species providing a plausible mechanism for observed habitat separation. IRELAND

DIETARY ANALYSIS OF SYMPATRIC ARCTIC CHAR AND BROWN TROUT IN LOUGH MUCKROSS, SOUTH-WESTERN IRELAND

Stable isotope analysis was used to examine dietary separation between sympatric Arctic char (Salvelinus alpinus (L.)) and brown trout (Salmo trutta) in Lough Muckross, Co. Kerry, and to test the applicability of the interactive segregation hypothesis to observed trophic relationships. Gut contents showed both species fed seasonally on similar prey. Stable isotopes indicated the long-term nature of the similarity in feeding relationships, with results providing no support for the interactive segregation hypothesis as used to explain dietary differences between the species in Scandinavian lakes. Feeding and capture patterns indicative of differences in habitat use were consistent with the MacArthur niche compression hypothesis, with differences in temperature preferences for both species providing a plausible mechanism for observed habitat separation.

CURSORIAL SPIDERS (ARACHNIDA: ARANEAE) IN THE CHIHUAHUAN DESERT OF WESTERN TEXAS, U.S.A

A pitfall trap survey of spiders was conducted on the Dalquest Research Site in the Trans-Pecos counties of Brewster and Presidio, Texas, within the northern Chihuahuan Desert, U.S.A. During 13.5 months 1,326 spiders were collected from two separate habitats. Sixty-six recognizable species representing 24 families and 46 genera were identified. The habitats, which were 800 m apart, had 20 shared species. The Sandy Canyon Site contained 29 unique species, whereas the Camp Site contained 17. Sites differed in vegetation, elevation, soil type, and availability of water.

Ontogenetic habitat shift and risk of cannibalism in the common chameleon (Chamaeleo chamaeleon)

Ontogenetic habitat shifts have been documented in numerous fish and amphibians and in some reptiles. Intraspecific competition together with differential predation, prey size, social interactions, size-related thermal requirements, and morphological constraints on movement are often implicated in this ontogenetic habitat separation. In the current study, we combined field observation with experiments in seminatural arenas to test various hypotheses regarding the ontogenetic habitat shift that we have documented in the common chameleon. Juveniles (mean, 1 g) occupied low grasses and the adults (mean, 35 g) were found on bushes and trees. Overlap in habitat use between these two age classes was minimal. Our field experiments showed that juveniles actively avoid the presence of adults by concealment or flight. Adults readily attacked and consumed juveniles, regardless of their own mass. These results suggest that the risk of cannibalism towards juveniles is an important selective force behind the ontogenetic habitat shift observed in the common chameleon and may be important in other species too.

Vertical zonation patterns of scavenging amphipods from the Hadal zone of the Tonga and Kermadec Trenches

Deep-sea trenches present an ideal system in which to study vertical zonation, though the difficulties inherent in studying these great depths have thus far deterred such research. Here, we present the first account of the structure and vertical zonation of the scavenging guild residing in the hadal habitat of the Tonga and Kermadec Trenches (SW Pacific Ocean). Four species of scavenging amphipod ( Eurythenes gryllus, Scopelocheirus schellenbergi, Hirondellea dubia, and Uristes sp. nov.) were captured with baited free-vehicle traps set 1 m above the seafloor and deployed to bottom depths between 5155 and 10,787 m. Each species occupied a distinct vertical zone of 3.5 km or less, and the scavenging amphipod assemblage vertically partitioned the hadal zone. Scavenging amphipod diversity and evenness sharply declined below 9 km. For S. schellenbergi and H. dubia, population structure was stratified ontogenetically. Early instars appeared to reside exclusively in the shallower depths of each species’ vertical zone, and were functionally missing from the median and deeper regions. We captured brooding Uristes sp. nov. females, documenting the first bait-attendance event of brooding amphipods in the hadal zone. Separation of habitat in conjunction with deviations in reproductive traits, behaviors, and nutritional strategies may facilitate the coexistence of these four related species in this harsh and confining habitat.

Comparison of arthritis characteristics in lowland Gorilla gorilla and mountain Gorilla beringei

Gorilla gorilla and the less-studied G. beringei occupy very different, geographically separate habitats. We studied the occurrence of various forms of arthritis to examine possible nature/nurture causality. The macerated skeletons of 38 G. beringei and 99 G. gorilla individuals were examined macroscopically for the presence of articular and osseous pathologies. Contrasting with only isolated osteoarthritis and infectious arthritis was the frequent occurrence of a form of erosive arthritis associated with joint fusion. Twenty-one percent of the G. beringei and 20% of G. gorilla specimens were afflicted, which are statistically indistinguishable frequencies. While both had prominent axial disease, they differed in patterns of peripheral arthritis. Whereas G. beringei showed a pauciarticular pattern, the pattern in G. gorilla was more often polyarticular. Susceptibility to spondyloarthropathy was apparently genetically imprinted before Gorilla separated into G. gorilla and G. beringei. However, the different patterns of peripheral joint involvement suggest a causality resulting from lifestyle (e.g., the presence/absence or extent of knuckle walking) or a habitat-related infectious agent.

Prey selection and dietary overlap of shortfinned (Anguilla australis) and longfinned (A. dieffenbachii) eels during summer in the Horokiwi Stream, New Zealand

Benthic macroinvertebrates were collected and the diets of shortfinned eels (Anguilla australis) and longfinned eels (Anguilla dieffenbachii) inhabiting a small coastal New Zealand stream were examined to investigate intraspecific and interspecific trophic partitioning and prey selection. Our results showed intraspecific segregation of preferred prey among three size classes of juvenile shortfinned eels, but there was significant overlap between different size classes of longfinned eels. All size classes of both species of eel fed nocturnally on similar prey, and so there was no indication of temporal or trophic segregation. Therefore, habitat separation is assumed to be the main mechanism to reduce interspecific competition in these two co‐occurring species of eels.

Do Habitat Actions Affect Juvenile Survival? An Information‐Theoretic Approach Applied to Endangered Snake River Chinook Salmon

AbstractWe used 11 years of parr‐to‐smolt survival estimates from 33 Snake River sites to demonstrate that despite a number of confounding factors higher numbers of past habitat remediation or enhancement actions are associated with higher parr‐to‐smolt survival of endangered wild Snake River spring−summer (stream‐type) Chinook salmon Oncorhynchus tshawytscha. Information‐theoretic weights were applied to help distinguish between statistical models based on their relative plausibility. In the models with the highest estimated weights, actions taken to improve fish habitat showed a positive association with increased parr‐to‐smolt survival. However, because the actions were not sited randomly on the landscape, and because the actions may also have influenced other potentially important covariates, it is difficult to separate habitat action effects from effects due to other important factors.

Habitat preferences of tree pipit (Anthus trivialis) and meadow pipit (A. pratensis) at sympatric and allopatric localities

Habitat preferences of the tree pipit (Anthus trivialis) and the meadow pipit (A. pratensis; Passeriformes: Motacillidae) were observed during the years 1998–1999 at three localities in the Czech Republic; two with one pipit species only, and a third with both species present. We investigated one of the possible mechanisms allowing syntopic coexistence—different habitat selection. We characterised territories of each pipit pair by the habitats present in the territory (defined by dominant plant composition) and by quantitative parameters (territory size, height and density of the vegetation, number of look-outs of different height categories, and proportion of wet ground). Tree pipits preferred significantly higher vegetation of lower density than meadow pipits, and there was generally a higher number of high look-outs in their territories. However, in some of the preferred territories at the allopatric locality of the tree pipit, steep hill slopes could well substitute for higher look-outs, which were almost absent. The two pipit species at the sympatric locality occupied very different habitats, which was also reflected in quantitative parameters of their territories. The available data of pipit habitat at different European localities show that the two species can occupy a much wider range of habitats. The habitat separation in sympatry might therefore be one of the mechanisms allowing syntopic coexistence of both species.

Experimental hybridization between two recently diverged species of tropical sea urchins, Echinometra mathaei and Echinometra oblonga

Summary Two species of tropical sea urchins, Echinometra mathaei and Echinometra oblonga, occur abundantly on Okinawan intertidal reefs; E. mathaei is found mainly on inshore reef flats while E. oblonga burrows in the offshore reef margins. The two species spawn during the same season, and hybrid embryos can be formed in the laboratory. We confirmed earlier experiments showing that fertilization rates are high between eggs of E. oblonga and sperm of E. mathaei, but significantly lower than those in homogametic crosses, whereas few eggs of E. mathaei are fertilized by sperm of E. oblonga, even at very high sperm concentrations. If they spawn together in the field, most or all ova of E. oblonga would be fertilized by conspecific sperm before encountering sperm of E. mathaei on the reef flat, so hybridization is partially minimized by habitat separation. However, many viable sperm of E. oblonga would still be available to fertilize ova of E. mathaei. Species-specific differences in sperm chemotaxis or gamete compatibility may provide prezygotic barriers that also would prevent hybridization, especially between ova of E. mathaei and sperm of E. oblonga. We found that homogametic crosses reach peak fertilization levels much sooner than heterogametic crosses, even between ova of E. oblonga and sperm of E. mathaei, indicating the presence of prezygotic barriers to hybridization in the gametes. Nevertheless, laboratory crosses between E. mathaei and E. oblonga in both directions produced viable hybrids that developed through larval and juvenile stages to sexually mature adults. Phenotypic color pattern of hybrids tended to be maternal while other characteristics were intermediate (test size, weight, spine length, growth, tubefoot and gonad spicule morphology, pedicellaria valve length, gamete size). Adult F1 hybrids from both combinations were completely fertile and exhibited high fertilization rates in backcrosses. On the other hand, intensive field surveys failed to find hybrids, showing the rarity or absence of natural hybridization. These results mirror those found with hybridization studies on other species of Echinometra on Okinawa. They further support the conclusion that prezygotic isolating mechanisms such as habitat segregation as well as species-specific sperm chemotaxis and/or gamete compatibility have a role in maintaining the genetic integrity of these species.

Separation of foraging habitat among breeding sites of a colonial marine predator, the northern fur seal (Callorhinus ursinus)

This study examines whether lactating northern fur seals (Callorhinus ursinus) from different breeding sites on the Pribilof Islands in the eastern Bering Sea forage in separate areas. Satellite transmitters were attached to 97 northern fur seal females from nine breeding areas for 119 complete foraging trips during the 1995 and 1996 breeding seasons. Females from St. Paul and St. George islands tended to travel in different directions relative to their breeding site in both years of the study. St. Paul Island females dispersed in all directions except to the southeast, where St. George Island females foraged. Habitat separation was also observed among breeding areas on northeastern and southwestern St. Paul Island and to a lesser degree on northern and southern St. George Island. Although foraging direction led to geographical separation among sites, the maximum distance traveled and the duration of foraging trips did not differ significantly among islands in either year. The results of this study document that lactating fur seals from the same site share a common foraging area and that females from different breeding sites tend to forage in separate areas and hydrographic domains.

Habitat separation in a species‐rich assemblage of jumping spiders (Araneae: Salticidae) in a suburban study site in Zimbabwe

AbstractA 40‐species assemblage of jumping spiders inhabiting a small (0.6 ha) tropical suburban study site in Zimbabwe was studied over 4 years. It was hypothesized that marked habitat separation is one of the critical factors permitting the close coexistence of so many species from the same family (Salticidae). The 25 most common salticids (i.e. species with 10 or more records) were found to occupy six primary habitat types: tree trunks (with three salticid species), tree leaves (two species), shrubs (five species), walls (three species), low herbaceous plants and grasses (three species) and ground and litter (six species). The remaining three species, termed habitat generalists, frequented three or more of these habitats. Finer‐scale microhabitat separation was also recorded in many species. The remaining 15 less common species (i.e. <10 records) could not be assigned to particular habitats with certainty. Twenty‐one (84%) of the 25 common salticids showed a significant association with a single primary habitat type. Three‐quarters of species were present for 3 or 4 years of this 4‐year study. It was concluded that the narrow spatial niches occupied by most species, combined with the numerous microhabitats within the site, were conducive to the highly diverse salticid assemblage. Attention is drawn to the problems of long‐term sampling of such a small area without undue disturbance to the fauna. The impacts of long‐term weather cycles on habitats, ephemeral niches, age‐dependent use of habitats, inter‐ and intraspecific associations of individuals within habitats, and the relationship between suburban and wild habitats are discussed. Suburban environments, by providing a wide range of microhabitats, can support a high diversity of salticid species and thus contribute to their conservation.

Endangered Species Constrained by Natural and Human Factors: the Case of Brown Bears in Northern Spain

Abstract: We developed a conceptual framework for classifying habitat quality that requires the construction of separate habitat models for each key demographic feature; the framework can be applied when the factors that determine different demographic processes differ substantially. For example, survival of large carnivores is mainly determined by human‐induced mortality, whereas nutritional condition determines reproductive rate. Hence, a two‐dimensional habitat model built for reproduction and survival yields five hypothetical habitat categories: matrix, with no reproduction and/or very high mortality; sink, with low reproduction and high mortality; refuge, with low reproduction and low mortality; attractive sink, with high reproduction and high mortality; and source, with high reproduction and low mortality. We applied this framework to two endangered brown bear ( Ursus arctos ) populations in the Cantabrian Mountains, Spain. Our aim was to generate working hypotheses about the quality and spatial arrangement of bear habitat to analyze the present conditions of the different population nuclei and to facilitate identification of core areas of high conservation value, conflictive areas, or areas with unoccupied potential habitat. We used a geographic information system and two spatial long‐term data sets on presence and reproduction and performed logistic regressions for building a two‐dimensional model. The analysis reveals that both populations exist under different suboptimal conditions: the eastern population mainly occupies areas of suboptimal natural habitat and relatively low human impact, whereas the western population is located mainly in areas with high human impact but otherwise good natural quality. To test hypotheses about demographic features of the obtained habitat categories, we classified data on historic extinction in northern Spain ( fourteenth to nineteenth centuries ) with the two‐dimensional model. Extinction probabilities within each habitat category confirmed the hypotheses: most extinctions occurred in matrix habitat, and the fewest occurred in source habitat.

Sexual difference in habitat use of Texas map turtles (Emydidae: Graptemys versa) and its relationship to size dimorphism and diet

Sexual differences in habitat use of map turtles (Graptemys spp.) have been attributed to differences in swimming ability as influenced by body size, because females are much larger than males, or to sexual differences in diet. Captures of young female Graptemys versa, which had body sizes similar to those of adult males but diet and trophic morphology more similar to those of larger females, allowed testing of these alternative hypotheses. A variety of single habitat variables measured at the sites of capture performed poorly in separating the three groups of turtles, but multivariate analysis and variables relating to position within the stream produced greater separation, indicating that complex combinations of factors probably influence habitat use. Young females were more similar in their habitat use to large females than to males, and their diet was also more similar to that of larger females, due primarily to the quantities of mollusks consumed. The data supported the hypothesis that habitat separation was the result of dietary rather than body size differences. While dietary differences are probably facilitated by sexual size dimorphism, they may not be the ultimate selective force that produced the size dimorphism.

Habitat Separation among Three Species of Water Snakes in Northwestern Kentucky

Historical records and recent studies indicate that populations of the Copperbellied Watersnake (Nerodia erythrogaster neglecta) are in decline. Reduction in range and fragmentation of populations are largely based on human activities, primarily through alteration of shallow wetlands. We conducted a comparative study of habitat use to determine why N. e neglecta may be more vulnerable to human-induced changes than sympatric congeners. Nerodia erythrogaster neglecta were observed primarily along shorelines with gentle slopes near very shallow water and often used herbaceous vegetation, logs, grasses, and sedges substrate categories. Nerodia sipedon pleuralis used habitat most similar to N. e. neglecta. Although N. s. pleuralis were observed to be more aquatic and were more often found in open water, they showed the same close association with shorelines and basking substrates as N. e. neglecta. Nerodia rhombifer is the least selective in habitat use of the three species and is the least similar in habitat use to N. e. neglecta in this study. As a whole, the results of this study support previous research that suggests N. e. neglecta is a seasonal habitat specialist. The extensive destruction of seasonal wetlands in the Midwest may thus have a greater impact on N. e. neglecta than their sympatric congeners.

Evidence of connectivity between juvenile and adult habitats for mobile marine fauna: an important component of nurseries

A critical link missing from our understanding of the nursery role of specific marine habitats is the evidence of connectivity between juvenile and adult habitats. This paper reviews and evaluates evidence of, and spatial scales for, movements from juvenile to adult habitats and it sum- marises the methods used to study movements. Examples include many fish families but few inverte- brate taxa, and most are species of economic importance for USA and Australia. The types of juvenile habitat range from the entire estuary or shallow open coastal waters to specific habitats within estu- aries or coastal waters; in some cases juvenile habitats include habitats not traditionally regarded as nursery areas (e.g. the surf zone). The duration of time spent in juvenile habitats averages 13 mo (range 8 d to 5 yr). The majority of organisms move distances of kilometres to hundreds of kilometres from juvenile to adult habitats, although the scale of movements ranged from metres to thousands of kilometres. Changes in abundance among separate habitats and the progression of size classes among separate habitats are the main methods used to infer movement and habitat connectivity. Spa- tial partitioning of stages of maturity, natural parasites, and a variety of artificial tagging methods have also been used. The latter will become more useful with continued developments in the minia- turisation of artificial tags. More recent studies have used natural tags (e.g. trace elements and stable isotopes) and these methods show great promise for determining movements from juvenile to adult habitats. Few studies provide good evidence for movement from specific juvenile habitats to adult habitats. Future studies need to focus on this movement to supplement data on density, growth and survival of organisms in putative nursery habitats. Such information will allow management and con- servation efforts to focus on those habitats that make the greatest contribution to adult populations.

Incorporating Landscape Attributes into Models for Migratory Grassland Bird Conservation

Abstract: We evaluated the influence of local and landscape attributes on the occurrence and density of seven passerine species in grasslands (n = 380) throughout eastern South Dakota ( U.S.A.). Landscape composition and land cover were quantified at three spatial scales: 400‐, 800‐, and 1600‐m radii from the transect center. Separate habitat models were generated for mixed‐grass and tallgrass prairie regions to depict the way birds respond to geographic variation in local and landscape structure. Sedge Wrens ( Cistothorus platensis) and Clay‐colored Sparrows ( Spizella pallida) in the mixed‐grass and tallgrass regions used both large and small patches if they were embedded in a landscape with a high proportion of grassland habitat. Occupancy rates for these species were higher in small patches within landscapes with high grassland abundance than in large patches within low grassland landscapes. Grasshopper Sparrows (Ammodramus savannarum) and Dickcissels ( Spiza americana) in the mixed‐grass region and Savannah Sparrows ( Passerculus sandwichensis) in the tallgrass region were area‐sensitive species that used large grassland patches regardless of landscape configuration. The occurrence of Savannah Sparrows in both regions and Sedge Wrens, Grasshopper Sparrows, and Western Meadowlarks ( Sturnella neglecta) in the mixed‐grass region was negatively associated with an increase in patch edges with trees. Explained variation in density estimates was associated only with local patch and vegetation variables. Individual species demonstrated scale‐dependent differences in the way they perceived habitat and in their response to regional landscape structure. These findings provide evidence that results from one region may not be extrapolated to others because they may vary with species distribution, vegetation structure, and landscape composition. Assessments of regional grassland bird habitat must be conducted at multiple scales because some species respond only to local conditions within grasslands, whereas others respond to habitat structure at landscape scales.

Development of an ecological mapping methodology for urban areas in New Zealand

At present there is no ecologically based mapping system designed for application to urban areas in New Zealand. New Zealand’s ecological structure is particularly interesting as it combines indigenous habitats comprising significant numbers of endemic species with a vibrant imported ecology comprising habitats characteristic of their primarily European and Australian origins. In New Zealand, the focus to date in habitat mapping has been on developing vegetation mapping techniques for application to predominantly indigenous habitats in rural areas. Thus, they omit reference to the type of mixed exotic-indigenous vegetation associated with habitats common to urban areas, such as cliff faces, disused quarries, private gardens and grounds, river and rail corridors. A project was undertaken in conjunction with the Dunedin City Council to develop a habitat map of the city. The aim was to produce a map that would accommodate the diverse highly modified habitats characteristic of Dunedin and that would incorporate all types of urban open space ranging from indigenous habitats, such as forest to exotic habitats such as lawns, and residential gardens. The project developed a land use and habitat classification hierarchy applicable to the New Zealand urban context, including a classification system for private gardens. This paper describes the classification system that was developed, its benefits, limitations and application. The map is the first attempt to record all natural land uses, including gardens in any New Zealand city at a detailed level, i.e. at a scale of 1:3000. In all 1100 separate habitat parcels were mapped. The map revealed that whilst Dunedin is a city rich in natural vegetation very little of this is indigenous or even predominantly indigenous vegetation. A Geographic Information System was used to map the urban habitats and store the habitat data. The habitat map and associated data will be used by the council in developing an open space strategy for the city.