Bare Habitats Research Articles

The foraging ecology of the gray rat snake (Elaphe obsoleta spiloides). II. Influence of habitat structural complexity when searching for arboreal avian prey

AbstractA predator's behavior and success when foraging can be compromised by a variety of environmental factors. We examined the effect of variation in habitat structural complexity on the predatory success of the semiarboreal gray rat snake (Elaphe obsoleta spiloides) foraging for arboreal bird nest contents. Individual snakes searched for nests in enclosures containing one of five levels of vegetation density that reflected the range of structural complexity measured at a field site where predator and prey species are common. Subjects were most proficient at locating prey in enclosures having low levels of structural complexity, and experienced decreased predatory success in barren or highly-complex habitats. Ten behaviors comprised over 95% of the trial durations, and four of these occurred more often than the other six regardless of variation in structural complexity within the enclosure. We suggest that low levels of structural complexity offer snakes concealment from predation while not obscuring their view of provisioning activity at the nest.

Influence of habitat on abundance and size structure of a large temperate-reef fish, Achoerodus viridis (Pisces: Labridae)

The relationship between densities of Achoerodus viridis (Pisces: Labridae) and reef habitats at various localities within New South Wales (NSW), Australia was examined. Types of habitats were quantified at inner, mid and outer estuarine locations in each of two estuaries (Botany Bay and Port Jackson) to determine whether purported patterns of movement from estuaries could be related to differences in habitat. Although the same types of habitat were generally found at all locations, differences in the proportion of habitat types were found between shallow and deep reefs and among inner, mid and outer estuarine locations for both estuaries. Shallow habitats were usually dominated by Ecklonia radiata, turf and/or fringe habitat in Botany Bay, whereas deep sites were generally dominated by urchin-grazed barrens habitat and, sometimes, sponge- and ascidian-dominated deep reef. Shallow sites in Port Jackson were dominated by a mixture of habitats, as were deep reefs at mid-estuarine locations. Other deep reefs in Port Jackson were dominated by E. radiata (inner estuarine) or barrens (outer estuarine) habitat. Thus, patterns of habitat cover were not consistent between estuaries and numbers of fish could not be related to proportional representation of habitat on reefs along estuarine gradients. Univariate and multivariate analyses showed that there was little evidence that any size class of fish was correlated with the proportional representation of a particular habitat or group of habitats. Counts of fish that focused on barrens and E. radiata forest habitats over a period of 10 yr showed that similar numbers and all sizes of fish were found in the two types of habitat. Greater numbers of small fish were, however, found in the E. radiata forest habitat than in the barrens habitat. Estimates of abundance along the coast of NSW (100s to 1000 km) in a range of habitats (e.g. ascidian-dominated reef, kelp forest, urchin-grazed barrens) showed that there was no indication that a particular habitat consistently had greater numbers of A. viridis than other habitats. Therefore, A. viridis of a range of sizes appears to be flexible in its use of habitats on reefs.

Assessing Land-Use Impacts on Natural Resources

/ Much information is available on changes that occur in natural resources from both spatially-explicit data on environmental conditions and models of the interactions of these conditions and resources with human activities. The strategy for assessing land-use impacts on natural resources developed in this paper provides a framework for using relevant data and models to address questions of how management practices can promote both use and protection of resources. This assessment strategy integrates spatially explicit environmental data using geographic information systems (GIS) with computer models that simulate changes in land cover in response to land-use impacts. The computer models also simulate susceptibility of species to changes in habitat suitability and landscape patterns. The approach is applied to management of limestone barrens on the Oak Ridge Reservation in East Tennessee. Potential limestone barrens habitats are identified by overlaying appropriate soils, geology, slope, and land-use/land-cover conditions. Their validity is tested against known sites containing rare species that occur in these habitats. The location of habitats at risk in the aftermath of human activities is determined by using an available area model that identifies the size and proximity of sites that particular types of species can no longer use as habitat. The resulting risk map can be used in land management planning. The approach uses readily available in situ and remotely sensed data and is applicable to a wide range of locations and land-use scenarios. This approach can be refined based on needs identified by land managers and on the sensitivity of the results to the resolution of available resource information.KEY WORDS: Land management; Assessment; Habitat characterization; Limestone barrens; Ecological modeling; Geographic information systems

Environmental Influences upon the Social Choices, Occupational Behaviours and Adaptedness of Zoo Chimpanzees: Relevance to Occupational Therapy

This study investigated adaptedness within an institutional setting with a captive chimpanzee model, asking the question: What is the relationship of environmental opportunities for occupation, of the lack thereof, to adaptation? Eleven group-living chimpanzees at the Los Angeles Zoo were studied across three common environmental conditions: new enrichment, in which materials were introduced into their habitat to support diverse occupations; old enrichment (days after new enrichment); and no enrichment (barren habitat). Shifts in social and occupational choices across conditions were analysed quantitatively and qualitatively. While the chimpanzees employed various adaptive strategies that favourably influenced their experiences of time's passage, their adaptive capacities were also environmentally overwhelmed. Time emerged as an environmental factor that created situations of occupational deprivation and also channelled behaviour into more constricted forms of expression. It is proposed that the findings here may be particularly germane to persons who frequently confront empty time (little availed by what there is in the environment to do) or, more seriously, occupational deprivation. Specific considerations for occupational therapists are developed with respect to three key constructs: environment, adaptation, and occupation.

Density dependent foraging of sea urchins in shallow subtidal reefs on the west coast of Italy (western Mediterranean)

The ecological role of the sea urchins Paracentrotus lividus and Arbacia lixula was examined in shallow subtidal reefs on the west coast of Italy from December 1994 to July 1996. The density of sea urchlns was manipulated experimentally in patches of vertical substrata without erect algae. The following propositions were examined: (1) that sea urchins were responsible for the persistence of patches of bare rock and encrusting coralhnes in shallow subtidal habitats, (2) that their effects were density dependent, and (3) that these effects were consistent in time. The experimental manipulations consisted of 3 replicate patches randomly assigned to one of the following treatments: ( l ) Ox (total ren~ovals), (2) 0 5 x (50% of the average density found in untouched patches), ( 3 ) l x (untouched patches), and (4) 2x (200% of the average density found in the untouched patches). The removal of sea urch~ns significantly increased the coverage of the filamentous and fleshy algae in permanent plots, and these effects were cons~stent over time. In contrast, grazing had no effect on the encrust~ng coralhnes, Peyssonnella spp. and invertebrates (barnacles, bryozoans and limpets) The response of the filamentous algae was proportional to the density of sea urchins, with percent cover values In the 0 5 x treatment being intermediate to those observed in the Ox and l x treatments. Conversely, the response of the fleshy algae was non-linear: only when sea urchins were totally removed d ~ d the coverage of these plants lncrease significantly. Doubling the density of sea urchins significantly increased the erosion of the margins of the patches, while their removal caused no change along the perimeter. In general, there was considerable variability from patch to patch in the abundance of most of the response vanables analysed, while temporal changes were less important. The results show that sea urchins can have significant but variable effects on vertical patches of barren habitat; alternative explanations are suggested to account for the persistence of these patches despite the removal of grazers.

Marine, Brackish, and Freshwater Fish Communities in the Vegetated and Bare Shallows of an Australian Coastal River

Fish communities found in the marine, brackish, and freshwater shallows of the Clarence River (New South Wales, Australia) were sampled over a 12-mo period to compare communities inhabiting bare and vegetated substrata. A total of 26,107 fish representing 57 species and 36 families was collected biomonthly suing a 6-mm mesh siene. Permanent residents (i.e., species found throughout the year) were primarily gobies (Gobiidae) and gudgeons (Eleotridae). Juveniles of many species found as adults in other parts of the river were seasonally abundant in the shallows. Most numerous was a small ambassid, the glassy perchlet (Ambassis jacksoniensis), the majority of which was collected from marine and brackish regions of the river. Firetail gudgeons (Hypseleotris compressus) were caught in highest numbers at the freshwater sites. Cluster analysis suggested that fish communities in widely separated vegetated sites were more similar to each other than to those in adjacent bare sites. Shallow vegetated (Zostera capricorni) habitats in the marine region of the river had greatest diversity and highest abundances of fish, particularly during recruitment periods. At these times, juveniles of many commercially important species were captured, including yellowfin bream (Acanthopagrus australis), sea mullet (Mugil cephalus), flat-tail mullet (Liza agentea), tarwhine (Rhabdosargus sarba), luderick (Girella tricuspidata), silver biddy (Gerres subfasciatus), and sand whiting (Sillago ciliata). The vegetated (Vallisneria gigantea) sites in the brackish region also had significantly more species and individuals during recruitment periods (spring) than bare sites. Although freshwater vegetated sites consistently had more individuals than freshwater bare sites, there were no significant differences in species richness between vegetated and bare habitats. The need to conservatively manage shallow-water fish habitats is stressed. *** DIRECT SUPPORT *** A01BY073 00004

Feeding ecology of the temperate marine fish Achoerodus viridis (Labridae): Size, seasonal and site-specific differences

Fish were collected from localities in the Sydney region, New South Wales, Australia, from March 1991 to September 1993. Achoerodus viridis is a benthic carnivore and consumes a wide variety of prey items. Size-specific differences in diet were found. The diet of recruits (17-26 mm SL) collected in seagrass environments was dominated by tanaids, whereas that of rocky reef recruits was dominated by harpacticoid copepods. The diet of rocky reef fish then shifted to gammarid amphipods and other crustaceans (fish 50-150 mm SL) and to mussels and urchins (fish >300 mm SL). Juvenile fish on rocky reefs (450 mm SL) foraged in shallow fringing habitat, whereas adult fish (>200 mm SL) foraged in deeper turf and barrens habitats, reflecting the depth distribution of the species. Feeding rate of larger fish tended to be less than that of smaller fish. Variations in diet and feeding rate were also detected over the year but the patterns were not consistent between years. Among sites, there were differences in diet but these were not related to the position of sites inside an estuary or on the open coast. The results of this study provide information on the feeding ecology of a large labrid fish; this information will aid in understanding the population dynamics of the species.

Survival of kelp adjacent to areas grazed by sea urchins in New South Wales, Australia

Abstract The sea urchin Centrostephanus rodgersii grazes areas of reef free of large brown algae (the barrens habitat). Survival of the kelp Ecklonia radiata adjacent to patches of barrens habitat was compared to that in the centre of kelp forests (centre) and edges of forests not adjacent to patches of barrens habitat (ungrazed). Estimates of rates of instantaneous mortality for tagged plants, as described by the slope of a negative exponential model (± 95% CI) were: barrens, 0.078 ± 0.004; centre, 0.051 ± 0.004 and ungrazed edge, 0.065 ± 0.007. Survival of plants was greatest in the middle of forests and least on the margins of patches of barrens habitat. A significant proportion of mortality in the barrens and centre positions was caused by herbivorous fish. When these plants were excluded from analysis there were no significant differences in survival between the barrens and ungrazed positions. It is concluded that C. rodgersii has little impact on the abundance of Ecklonia outside sharply defined boundaries.

Biotopval, populationsutveckling och häckningsbiologi hos skärpiplärka Anthus spinoletta littoralis i ett småländskt skärgårdsområde

A population of breeding Rock Pipit Anthus spinoletta littoralis was studied in 1979—1990 in the archipelago off Oskarshamn in southeastern Sweden. Between 9 and 31 pairs were found breeding in the study area, at densities of 0.04–0.13 pairs/hectare in the different years. Population density declined abruptly between 1984 and 1985, probably due to harsh winter conditions. Territory size was usually 1–3 hectares. Average clutch size was 5.29 eggs/ clutch and 4.53 chicks/clutch. For their breeding Rock Pipits preferred habitats with stones, seaweed on the shoreline and a rich cover of low vegetation, to more barren habitats. Breeding success was higher in the preferred habitat.

Spatial Heterogeneity, Sea Urchin Grazing, and Habitat Structure on Reefs in Temperate Australia

The sea urchin Centrostephanus rodgersii is important in determining biogenic habitat structure on rocky reefs in New South Wales. Individual C. rodgersii, in common with other diadematids, are found in shelters during the day, from which they emerge to forage at night and maintain patches of barrens habitat. The effect of availability of shelter on the foraging behavior of C. rodgersii, and on the abundance of benthic invertebrates and algae, was investigated by a field experiment. Physical heterogeneity in the form of large boulders were translocated between the barrens and Ecklonia forest habitats and arranged so as to either maximize or minimize shelter. The fauna and flora on translocated boulders became progressively similar to that found in the surrounding habitat. Most obvious of these changes were reductions in the density of foliose algae on boulders moved from Ecklonia forest to barrens and reductions in the density of limpets in the reverse translocation. C. rodgersii recruited to all treatments irrespective of where the boulders came from, where they were moved to, and the amount of shelter provided. The availability of shelter was clearly a sufficient condition for the creation of areas of barrens habitat. The reliance on shelter by these sea urchins makes their local distribution and, therefore, that of the barrens habitat, more predictable than in other temperate regions.

An Analytical Treatment of Root-to-Shoot Ratio and Plant Competition for Soil Nutrient and Light

By restricting biomass allocation to two compartments only-roots and leaves-we are able to treat plant resource competition analytically. We derive A*i, the optimum allocation strategy for invasion into a bare habitat, and A*f, the allocation strategy of the dominant species in an equilibrium habitat. Furthermore, we prove that in a given habitat succession proceeds from species A*i to species A*f, as long as enough intermediate species are present. Analysis of the relationship between A*i and A*f and the soil nutrient supply and disturbance rates of a habitat predicts that a dichotomy exists in succession. Low soil nutrient supply and disturbance rates favor successions from rooty to leafy species, and high soil nutrient supply and disturbance rates favor the converse. Experimental research is needed to determine whether this pattern exists in nature. Light "consumption" by plants is fundamentally different from soil nutrient consumption in our model. This difference in light and nutrient consumption makes all possible two-species equilibria unstable and leads to founder control. In our model founder control can result in arrested succession and contributes to community diversity.

Exploitation ecosystems in heterogeneous habitat complexes II: Impact of small-scale heterogeneity on predator-prey dynamics

The model of exploitation ecosystems was re-analysed, assuming that habitat patches are so small that they form only parts of the home range of an individual predator. For habitat complexes where productive patches abound, the results suggested that predation will strongly spill over from productive patches, which set the tune for population dynamics within the whole landscape, to barren ones. This result conforms to the one obtained by T. Oksanen by assuming despotic habitat choice and essentially larger patch sizes. For habitat complexes heavily dominated by the barren habitat, spillover predation was predicted to be weak, as was the case in her large patch model. Unlike in her analysis, however, predation pressure was substantially reduced also within the productive habitat. In habitat complexes where patches are so small that they are exploited in a fine-grained manner, predation pressure was always found to be more intense in the barren habitat, contrary to the predictions of the original model of exploitation ecosystems. This analysis thus suggests that their model is applicable mainly on the landscape level. On the level of individual habitats, the applicability of their results depends on the habitat configuration (at its best for the prevailing habitat of the landscape and for moderate-sized patches of an essentially more productive habitat) and generally decreases with decreasing patch sizes.

Patterns in shallow subtidal marine assemblages along the coast of New South Wales

AbstractShallow subtidal areas of rocky reefs in central and southern New South Wales may best be described as a mosaic of habitats, the distributions of which are seemingly related to depth, wave exposure and a number of biological processes, particularly herbivory. The Fringe habitat is generally found only in the most shallow waters. Forests of the laminarian alga Ecklonia radiata are often found at intermediate depths. In deeper, or more sheltered water, sponges, ascidians and red algae are more abundant and the abundances of sea urchins and other invertebrate grazers decline. Overlying this broad‐brush pattern are patches of crustose coralline algae (the Barrens habitat), the distributions of which are not clearly related to depth. Invertebrate herbivores, and sea urchins in particular, are abundant in the Barrens habitat. The Barrens habitat was most represented at the more southern locations. At the two most northern locations, reefs were shorter in length and dominated by ascidians (Pyura species).

Exploitation ecosystems in heterogeneous habitat complexes

When the model of exploitation ecosystems by Oksanenet al. (1981) is re-analysed, using similar consumer-victim differential equations, but allowing dispersal between habitats differing in primary productivity, the relation between trophic dynamics and primary productivity turns out to be strongly dependent on the abundance relationships between different habitat types. In habitat complexes where a relatively productive habitat abounds, exploitation tends to ‘spill over' to the barren habitat, whose trophic dynamics thus become to a high degree driven by the dynamics in the productive habitat and entirely different from the predictions of Oksanenet al. (1981). Conversely, in habitat complexes where the barren habitat overwhelmingly prevails, the ‘spillover exploitation’ becomes strongly diluted. Consequently, local trophic dynamics within both habitats will behave approximately as predicted by the model of Oksanenet al. (1981).

Nest-site characteristics of prairie shorebirds

Nest-site characteristics of eight shorebird species were studied during the period 1982–1984 at Last Mountain Lake National Wildlife Area in south central Saskatchewan. Plant species composition at nests varied significantly among species and was correlated with distance to bare ground and aquatic habitat. Flora at Wilson's phalarope (Phalaropus tricolor) nests was correlated with clutch initiation date, reflecting a seasonal shift in nesting habitat. Species differed significantly in cover types at nests. For American avocet (Recurvirostra americana), killdeer (Charadrius vociferus), and Wilson's phalarope, cover types differed between nests and random sites; cover types also differed between nest cups and the immediate surrounding habitat for killdeer and Wilson's phalarope. Interspecific differences in nest-site vegetation physiognomy were portrayed by the first two factors of a principal components analysis, which accounted for 73 and 22% of variance in the data, respectively. Principal components analysis assembled species on a habitat gradient that varied according to cover type, and vegetation density and heterogeneity.

Adaptation to cold: energy metabolism in an atypical lagomorph, the arctic hare (Lepus arcticus).

Unlike other lagomorphs or any other mammals living in a cold environment, the basal metabolic rate of the arctic hare, Lepus arcticus monstrabilis (0.36 cm3 O2/g per hour) was only 62–83% of the values predicted from its body weight. The minimum thermal conductance (0.010 cm3 O2/g per hour per degree centigrade) was also reduced to only 51–59% of its weight-specific value (0.019–0.017 cm3 O2/g per hour per degree centigrade). The normal body temperature (38.9C), however, was comparable to that of other lagomorphs. The daily energy consumption between ambient temperatures of −24 and 12.5C was between 262 and 133 kcal, which is 6–43% above the minimum resting values at corresponding ambient temperatures.It is concluded that the reduction of surface area to volume ratio and the effectiveness of its insulation are sufficient compensations so that the arctic hare can maintain a normal body temperature with a depressed basal metabolic rate. Such a reduction of metabolism is energetically adaptive for a species living exclusively in a cold and relatively barren habitat.