High Disturbance Sites Research Articles

Isolation by disturbance: a pattern of genetic structure of the coral Pocillopora grandis in the Gulf of California

Genetic differentiation within species can be influenced by the distance between populations (isolation by distance, IBD) or by differences in the habitats they occupy (isolation by environment, IBE). Understanding the population structure and dynamics that influence genetic diversity within small (<100 km2) multi-use marine protected areas (MPAs) and varying disturbances or protections is relevant to better designing and managing them. Pocillopora grandis communities were studied at 10 different sites in the Gulf of California, Mexico. The comparison between sites inside and outside an MPA or whether the population structure followed IBD or IBE was investigated with the genetic marker HSP70B. Environmental heterogeneity was used to test for IBE, and was measured by comparing the present benthic communities by site and through analysis of satellite images, while distance was used to test for IBD. Mantel tests found that the population of P. grandis did not follow IBD or IBE. Instead, cluster analysis grouped low (no-take zones) and high (crown-of-thorns starfish outbreaks and highly visited by tourists) disturbance sites together with the remaining sites within and outside of the MPA in another cluster (ΦRT = 0.082, p = 0.007). Furthermore, lower genetic diversity was found at sites with low and high disturbance. Our results suggest that instead of IBE or IBD influencing the population structure, the protection and disturbance levels could have a correlation with genetic patterns (i.e. isolation by disturbance, ID). These findings will be valuable for MPAs in terms of efficient management of genetic diversity objectives by considering the appropriate spacing and protections, depending on how vulnerable a species is to disturbance.

How landscape traits affect boreal mammal responses to anthropogenic disturbance

Understanding mammalian responses to anthropogenic disturbance is challenging, as ecological processes and the patterns arising therefrom notoriously change across spatial and temporal scales, and among different landscape contexts. Responses to local scale disturbances are likely influenced by landscape context (e.g., overall landscape-level disturbance, landscape-level productivity). Hierarchical approaches considering small-scale sampling sites as nested holons within larger-scale landscapes, which constrain processes in lower-level holons, can potentially explain differences in ecological processes between multiple locations. We tested hypotheses about mammal responses to disturbance and interactions among holons using collected images from 957 camera sites across 9 landscapes in Alberta from 2007 to 2020 and examined occurrence for 11 mammal species using generalized linear mixed models. White-tailed deer occurred more in higher disturbed sites within lower disturbed landscapes (β = −0.30 [−0.4 to −0.15]), whereas occurrence was greater in highly disturbed sites within highly disturbed landscapes for moose (β = 0.20 [0.09–0.31]), coyote (β = 0.20 [0.08–0.26]), and lynx (β = 0.20 [0.07–0.26]). High disturbance sites in high productivity landscapes had higher occurrence of black bears (β = −0.20 [−0.46 to −0.01]), lynx (β = −0.70 [−0.97 to −0.34]), and wolves (β = −0.50 [−0.73 to −0.21]). Conversely, we found higher probability of occurrence in low productivity landscapes with increasing site disturbance for mule deer (β = 0.80 [0.39–1.14]), and white-tailed deer (β = 0.20 [0.01–0.47]). We found the ecological context created by aggregate sums (high overall landscape disturbance), and by subcontinental hydrogeological processes in which that landscape is embedded (high landscape productivity), alter mammalian responses to anthropogenic disturbance at local scales. These responses also vary by species, which has implications for large-scale conservation planning. Management interventions must consider large-scale geoclimatic processes and geographic location of a landscape when assessing wildlife responses to disturbance.

Population Structure and Regeneration Status of Woody Plants in Relation to the Human Interventions, Arasbaran Biosphere Reserve, Iran

Proper understanding of the diversity and natural structure of woody species and the impacts of human interventions are prerequisites for maintaining the remaining forests as well as restoration of deforested and degraded areas. This research was conducted to document the impact of human interventions on the population structure and the species diversity in the Arasbaran biosphere reserve in Iran due to the limited research and insufficient knowledge. The study area was divided into three adjacent sampling areas of low, medium, and high destruction intensity. Thirty fixed area 0.1-hectare plots were sampled to evaluate the composition, diversity, and species richness. Oak (Quercus macranthera), hawthorn (Crataegus meyeri), and maple (Acer campestre) were the top three dominant tree species at all the sites. The relative dominance of the top three species comprised 87.8% of the basal area of all species. The relative abundance of the top three species accounted for 68.1% of the species. The mean density and basal areas per tree across all three destruction statuses were 145 ± 59 stems ha−1 and 0.01 ± 0.005 m2 ha−1, respectively. The mean height of trees was different at low and high disturbance sites (4.6 ± 0.96 m and 3.37 ± 1.74 m, respectively). Due to the impact of human interventions on forest structure, composition, and diversity, conservation programs are recommended for implementation and in collaboration with local communities to employ management aimed at providing services for local people while restoring these forests. Basic ecological studies such as this study are the foundation to begin developing policies and management that meet multiple ecological and social goals.

Jaguars and pumas exhibit distinct spatiotemporal responses to human disturbances in Colombia’s most imperiled ecoregion

Abstract Coexistence of sympatric felids is facilitated by mutual avoidance and the partitioning of habitats, prey, and time. Anthropogenic disturbances disrupt this coexistence in fragmented landscapes, potentially triggering cascading influences in ecological communities. We used photographic data from 8,717 trap nights (November 2014–June 2016) at 87 camera trap sites in Colombia’s middle Magdalena River basin to compare spatiotemporal overlap among jaguars (Panthera onca), pumas (Puma concolor), their prey, and humans, at sites of high and low disturbance, as determined by the human influence index. Human disturbance events (e.g., domestic dogs, livestock, and humans, including armed hunters) comprised 38% of all photographs at high disturbance sites and 29% of all photographs at low disturbance sites. Differential spatiotemporal overlaps were recorded between felids and their prey at high versus low disturbance sites, with jaguars exhibiting only 13% temporal overlap with humans at high disturbance sites. Among prey, temporal overlap was greater than spatial overlap for both felids across the study area. Compared to jaguars, pumas displayed more temporal overlap with all anthropogenic variables and more spatial overlap with most anthropogenic variables, suggesting lesser sensitivity to human disturbances. This study provides the first insights into the responses of a threatened large carnivore, jaguar, to camera trap-derived human disturbance variables in an unprotected landscape. It also highlights the importance of using multiple disturbance types for evaluating human impacts on large carnivores.

Access Matting Reduces Mixedgrass Prairie Soil and Vegetation Responses to Industrial Disturbance

Substantial interest exists in understanding the role of low-disturbance construction methods in mitigating industrial impacts to native grassland soils and vegetation. We assessed soil and vegetation responses to conventional high-disturbance sod-stripping and revegetation on sandy soils, and the alternative practice of low-disturbance access matting to provide a temporary work surface on sandy and loamy soils. Treatments were associated with high-voltage transmission tower construction during 2014 within the Mixedgrass Prairie. High-disturbance sites were hydroseeded in May of 2015, while low-disturbance sites recovered naturally. We assessed soil physical (bulk density, water infiltration) and chemical properties (organic matter, pH, and electrical conductivity) after construction and herbage biomass for three growing seasons. Sod-stripping led to 53% greater soil bulk density and 51% less organic matter than nondisturbed controls, while water infiltration increased by 32% in these high-sand (>80%) soils. In contrast, access matting led to minimal soil property changes regardless of the texture. While total herbage biomass was unaffected by all construction treatments, sod-stripping reduced grass biomass by 80% during the first growing season, which coincided with a 119% increase in forb mass. Root biomass (0-15 cm) also declined 77% with sod-stripping. Vegetation biomass on sites with access matting remained largely unaffected by the disturbance. Overall, low-disturbance construction methods using access matting were more effective than sod-stripping in mitigating the negative impacts of industrial development on Mixedgrass soil properties, as well as vegetation biomass, and are recommended as a best management practice during industrial disturbance.

High human disturbance decreases individual variability in skink escape behavior.

Animals living around people may modify their antipredator behavior as a function of proximity to humans, and this response has profound implications for whether or not a population can coexist with humans. We asked whether inland blue-tailed skinks Emoia impar modified their individual antipredator behavior as a function of differential exposure to humans. We conducted multiple consecutive flushes and recorded 2 measures of antipredator response: flight initiation distance (FID), the distance from a threatening stimulus at which an individual flees, and distance fled, the distance an individual fled after a flush. We used a multiple model comparison approach to quantify variation in individual escape behavior across multiple approaches and to test for differences in between-individual variation among populations. We found that individuals tolerated closer approach and fled shorter distances at locations with relatively less human disturbance than at locations with medium and high human disturbance, respectively. In addition, skinks living at high human disturbance sites had less variable FIDs than at low human disturbance sites. Two theories may explain these results. Selection against less favorable phenotypes has reduced behavioral variation in urban habitats and behavioral plasticity allows individuals to flexibly adjust their behavioral patterns in response to human disturbance. These results highlight the importance of studying variation within populations, at the individual level, which may better elucidate the impact that human disturbance has on the behavioral composition of populations.

Behavioural tendencies associated with microhabitat use in a clonal gecko species living in the wild

Individual differences in behavioural traits influence habitat choice, and in turn, differences in used habitats shape different behavioural tendencies through plasticity. Here, I investigated the relationship between personality and microhabitat use in a free-living population of the clonal gecko Lepidodactylus lugubris. The study site is a small beachfront forest facing two environments with contrasting levels of human disturbance. I conducted a mark-recapture survey to assess the geckos’ spacing pattern and evaluated their boldness and exploration scores in the laboratory. The geckos exhibited a small range of movement and a high consistency in their perch height. Boldness was related to two microhabitat features, but exploration was not. Relatively shy geckos were found in trees near the roadside and on low branches, whereas relatively bold geckos were found on both the beachside and the roadside and on low to high branches. These patterns suggest that geckos in high-disturbance microhabitats may have frequently experienced artificial stimuli and become shy. However, the present results cannot exclude the possibility that individual differences are caused by other factors and that different personality types prefer and settle in different microhabitats. Although the actual mechanisms are unclear, my findings highlight that behaviour-related habitat use emerges even in clonal animals. Individuals within conspecifics show different spacing patterns and different behavioural tendencies. If clonal animals live in a spatially diverse environment, it is predicted that different microhabitats may gradually shape different personality types through developmental plasticity. Here, I investigated the association between the personality of clonal geckos and their microhabitat use in different levels of human disturbance. In contrast to the prediction, both juveniles and adults showed a similar pattern of boldness-related microhabitats; relatively shy individuals were found in putatively high-disturbance sites. This result suggests that the association between boldness and microhabitats is not gradually formed through a long-time scale but is likely generated within their early ontogenetic stage.

Variable interaction outcomes of local disturbance and El Niño-induced heat stress on coral microbiome alpha and beta diversity

Emerging evidence indicates that individual stressors can modify the coral microbiome; however, few studies have examined the impacts of multiple stressors through natural climatic events. During periods of low and high heat stress associated with the 2015–2016 El Nino, we tracked the microbiomes of two coral species (Porites lobata and Montipora aequituberculata) across sites on Kiritimati (Christmas) Island with different levels of local disturbance (i.e. subsistence fishing, pollution, dredging). At low heat stress, local disturbance was associated with increased microbial alpha diversity (i.e. number of microbial OTUs and their relative abundance) in both species and increased beta diversity (i.e. coral to coral variation in microbial community composition) in P. lobata. High levels of thermal stress subsequently elevated microbial beta diversity in both species at the low disturbance sites up to the level experienced at the high disturbance sites under low heat stress, illustrating that each stressor can destabilize the coral microbiome. However, with high heat stress microbial alpha diversity was no longer significantly different between disturbance levels for either species. Survival of P. lobata throughout the entire El Nino event was greater at low disturbance sites than high ones (40% vs. 15%), suggesting that protection from local stressors may enhance survival of stress-tolerant corals. However, no M. aequituberculata tracked in this study survived the thermal anomaly. Whether enhanced survivorship can be directly attributed to lower microbial diversity, however, remains to be tested. Overall, we found that, rather than acting synergistically, multiple stressors either acted antagonistically to one another (alpha diversity for both coral species, beta diversity for P. lobata) or exhibited dominance (beta diversity for M. aequituberculata), suggesting that multiple stressors cause various interaction outcomes on the coral microbiome and highlighting the need for future research to evaluate these interactions and their consequences for coral resilience.

Anthropogenic disturbance homogenizes seagrass fish communities.

Anthropogenic activities have led to the biotic homogenization of many ecological communities, yet in coastal systems this phenomenon remains understudied. In particular, activities that locally affect marine habitat-forming foundation species may perturb habitat and promote species with generalist, opportunistic traits, in turn affecting spatial patterns of biodiversity. Here, we quantified fish diversity in seagrass communities across 89 sites spanning 6° latitude along the Pacific coast of Canada, to test the hypothesis that anthropogenic disturbances homogenize (i.e., lower beta-diversity) assemblages within coastal ecosystems. We test for patterns of biotic homogenization at sites within different anthropogenic disturbance categories (low, medium, and high) at two spatial scales (within and across regions) using both abundance- and incidence-based beta-diversity metrics. Our models provide clear evidence that fish communities in high anthropogenic disturbance seagrass areas are homogenized relative to those in low disturbance areas. These results were consistent across within-region comparisons using abundance- and incidence-based measures of beta-diversity, and in across-region comparisons using incidence-based measures. Physical and biotic characteristics of seagrass meadows also influenced fish beta-diversity. Biotic habitat characteristics including seagrass biomass and shoot density were more differentiated among high disturbance sites, potentially indicative of a perturbed environment. Indicator species and trait analyses revealed fishes associated with low disturbance sites had characteristics including stenotopy, lower swimming ability, and egg guarding behavior. Our study is the first to show biotic homogenization of fishes across seagrass meadows within areas of relatively high human impact. These results support the importance of targeting conservation efforts in low anthropogenic disturbance areas across land- and seascapes, as well as managing anthropogenic impacts in high activity areas.

Development of a plant based riparian index of biotic integrity (RIBI) for assessing the ecological condition of highland streams in East Africa

The study of riparian plant communities along running streams offers information on the state of habitat and can help increase our knowledge on the use of bioindicators. We developed a riparian index of biotic integrity (RIBI) to evaluate the conditions of highland streams in response to anthropogenic disturbances in the southwest Ethiopian highland. To construct RIBI, we evaluated 22 potential plant metrics. Disturbance was quantified for each site using information on canopy openness, ground area without vegetation and exposed mineral soil. Five core metrics (floristic quality indexes, average C, native tree/shrub species, riparian status species and Shannon diversity index) were found to respond to anthropogenic disturbances. These metrics were significantly differentiated among sample sites categorized as low and high disturbance sites (p < .001). The core metrics and RIBI scores for this data set were also significantly correlated with environmental variables including riparian buffer width, dissolved oxygen, water temperature, turbidity, total suspended sediment, nitrate and orthophosphate. These findings provide support for the continued use of plants as indicators of highland stream condition in the East Africa, providing that the responses of plant based metrics to disturbances. Thus, the RIBI could be useful tool for the assessment and monitoring of stream ecosystems and evaluating the effect of stream restoration in the East African highland in the future.

Effects of Boreal Well Site Reclamation Practices on Long-Term Planted Spruce and Deciduous Tree Regeneration

Well site development associated with oil sands exploration is common in boreal mixedwood forests of northern Alberta, Canada, and necessitates reforestation to accommodate other land uses. Little is known about the impact of soil and debris handling strategies during well site construction on long-term forest regeneration. This study addresses the impact of soil disturbance intensity, debris treatment, soil storage, and planting on the reforestation of 33 well sites reclaimed prior to 2006. Data on the survival and growth of planted white spruce (Picea glauca (Moench) Voss) and the regeneration density of deciduous trees, including trembling aspen (Populus tremuloides Michx), are presented from 2014 to 2015. The survival of planted spruce increased from 81% to 88% at well sites with a high relative to low soil disturbance. The total tree densities were lower in most treatments (≤2.69 stems m−2) than those in clear cuts (5.17 stems m−2), with the exception of root salvage areas where clear cuts had greater balsam poplar (Populus balsamifera L.) densities (2.05 stems m−2 vs. &lt;0.71 stems m−2 on all other treatments). Aspen densities were up to five times greater at well sites with low disturbance when compared to those with high disturbance, and this was further aided by shallow mulch at low disturbance sites. Spruce growth did not respond to well site treatments. Aspen growth (diameter and height) remained similar between well site disturbance regimes; aspen exposed to high disturbance underperformed relative to low disturbance well sites and clear cut controls. With high disturbance, progressive soil piling led to increases in the density of aspen and birch (Betula papyrifera Marshall). Few long-term changes in soil were found due to well site development, with a greater soil pH in high disturbance sites compared to low disturbance sites. Overall, these results indicate that the nature of well site construction, including the extent of soil removal, soil piling, and debris treatment, may collectively alter forest re-establishment, with associated implications for forest management.

Intraspecific interactions shift from competitive to facilitative across a low to high disturbance gradient in a salt marsh

Disturbances are ubiquitous among salt marshes, and disturbances such as litter removal may form stressful environmental conditions. The stress-gradient hypothesis (SGH) predicts that the relative importance of facilitation and competition between species will vary inversely to each other across abiotic stress gradients. However, how intraspecific interactions vary across disturbance levels, and whether they follow the SGH has not been investigated. To test the SGH with intraspecific interactions within Suaeda salsa individuals, we assessed individual survival in established fully mapped salt marsh plots with two treatments, disturbed, litter removal and control, undisturbed plots. Recently developed spatial statistics were applied to distinguish between random processes, intraspecific facilitation, scramble competition, and contest competition underlying the spatial patterns at different spatial scales, growth stages, and disturbance levels. We found evidence that intraspecific interactions among S. salsa individuals across disturbance levels tended to support the SGH, but this support depended on time and space. Intraspecific interactions were more likely to show positive density dependence in disturbed plots, particularly at the seedling period and when individuals were separated by < 9 cm. However, positive density dependence was not detected in undisturbed plots. The protective effects of litter on seedlings, which were lost in undisturbed sites, may have been at least partly simulated at high seedling densities. Mortality in disturbed sites was not random, and facilitation had a more important influence than competition on population dynamics in high disturbance sites. However, the influence of competition on population dynamics, specifically scramble competition was also clearly important.

HUMAN DISTURBANCE AND THE PHYSIOLOGICAL RESPONSE OF ELK IN EASTERN WASHINGTON

Stress hormone measures have proven useful for assessing effects of human disturbance on wildlife populations. However, most studies are of short duration or limited geographic scope (i.e., without spatial replication), leading to concerns about confounding effects of biotic conditions. Previous research correlated fecal glucocorticoid metabolites (FGMs) of elk (Cervus elaphus) with human disturbance, but this factor also co-varied with seasonal climatic conditions, making it difficult to make broader inference regarding the role of human disturbance. In this study we attempted to simultaneously evaluate the effects of climatic conditions and human disturbance by comparing the year-round physiological stress response of elk to varying levels of human disturbance at three study sites in south-central Washington State. FGMs were consistently elevated throughout the year at the study site receiving the greatest amount of human disturbance. We observed support for a positive effect of precipitation and increasing temperature on FGMs at the low-disturbance site, but less support for importance of climatic variables in explaining FGMs at the high-disturbance sites - suggesting that climatic variables were likely of secondary importance compared to anthropogenic stressors in elk at those sites. Collectively, while we were unable to disentangle the effects of site- specific stressors, our findings suggest that in this environment, humans were a dominant stressor influencing FGM levels. Therefore, interpreting results of physiological studies requires that researchers account for a broad combination of biotic and abiotic stressors at a particular study location. We particularly encourage future investigators to account for the potential confounding effect of human disturbance that could override other stressors.

The strength of cross‐taxon congruence in species composition varies with the size of regional species pools and the intensity of human disturbance

AbstractAimOur aims were to determine whether cross‐taxon congruence of species composition patterns varies across regions and human disturbance levels and to infer whether these patterns relate to the size of the regional species pool and the sorting of species along a gradient of human disturbance.LocationAlberta's Boreal and Grassland Natural Regions, Canada.MethodWe compiled presence–absence data of four biological groups (birds, vascular plants, bryophytes and mites) from low and high disturbance sites in upland habitat. The cross‐taxon congruence across ecoregion and disturbance levels was analysed using Mantel and Procrustes tests. We applied resampling without replacement to generate confidence intervals to test for significant differences in strength of congruency between disturbance levels and ecoregions. We performed indicator species analysis to highlight how the species‐level response to high and low disturbance influences the pattern in community‐level cross‐taxon congruence.ResultsCross‐taxon congruence was stronger when all sites were considered than when high and low disturbance sites were considered separately. Congruency was relatively stronger in high than low disturbance sites in the Boreal ecoregion, but the pattern was reversed in the Grassland ecoregion. More species were indicators of undisturbed habitat than of highly disturbed habitats for all biological groups except for birds. Overall, biological groups that were poorly represented in a region and/or with few characteristic indicator species showed weak congruence in those sites.Main conclusionsWe conclude that a longer disturbance gradient can promote cross‐taxon congruence by increasing the species pool characteristic of low or high disturbance levels. Moreover, regional context can influence (or even reverse) the relative strength of cross‐taxon congruence in high and low disturbance sites, which may explain the inconsistent strength of cross‐taxon congruence along the disturbance gradient. To use biodiversity surrogates across biogeographical regions, it is therefore important to account for the regional and disturbance‐level dependence of cross‐taxon congruence.

Nest survival of Woodpigeons (Columba palumbus) in North African forests

Capsule The nesting success of the Woodpigeon Columba palumbus in oak forests in Morocco is affected by human disturbance and nest-site characteristics. Aims To determine factors affecting the nesting success of Woodpigeons subject to two levels of disturbance in a holm oak Middle Atlas forest. Methods Woodpigeon nests were monitored in highly disturbed (n = 30) and less-disturbed sites (n = 60) over two years (2010–11). Logistic-exposure models were used to estimate daily nest-survival rate and evaluate mechanisms (altitude, temporal factors, nest location, nest-site habitat and degree of human influence) affecting nest survival. Results Daily nest-survival rate was higher in less-disturbed sites (0.987; 95% CL: 0.980–0.991) than in high-disturbance sites (0.967; 95% CL: 0.949–0.978). Increasing density of trees surrounding nest sites and distance from the nest tree to the closest track increased daily nest-survival rate. Conclusions Less-disturbed sites confer better nesting conditions than highly disturbed ones. Management measures should control the access of vehicles, especially trucks, in the forest of the Middle Atlas and introduce a grazing regime that will allow the forest regeneration, which would improve Woodpigeon nesting success by increasing the density of holm oak trees.

Niche contraction of American chestnut in response to chestnut blight

Invasive pathogens can cause native population declines and change native species distributions, but the spatial limitations posed by disease are rarely explored. This study explored spatiotemporal variation in American chestnut ( Castanea dentata (Marsh.) Borkh.) survival over an 80-year period in response to the introduction of an invasive pathogen, chestnut blight ( Cryphonectria parasitica (Murrill) Barr), and identified changes in its current realized niche compared with its original niche. A study area in southwestern Virginia, USA, sampled historically for chestnut abundance before blight invasion, was resampled and measured for topography, soil chemistry, and forest composition. Pre-blight chestnut abundance was not significantly correlated to current chestnut abundance, suggesting that chestnut survival rate was not constant across stands. Results indicated that chestnut’s niche has shifted toward dry, high disturbance sites on southern- to western-facing slopes. This study provides evidence that chestnut is being constrained to a portion of its former niche following chestnut blight introduction because of spatial heterogeneity in survival rate.

Impact of long-term benthic trawl disturbance on sediment sorting and biogeochemistry in the southern North Sea

Benthic trawling has a recognised impact on sediment whole organism communities, yet little is known about its impact on sediment biogeochemistry. On 2 cruises in October 2001 and July 2002, we measured sediment characteristics (particle size distribution, porosity and organic matter (OM)) and sediment metabolism (oxygen uptake, denitrification, sulphate reduction and sediment- water nutrient exchange) along gradients of trawling activity at 14 sites in 2 regions of the southern North Sea: one with low tidal disturbance but high trawling disturbance (Outer Silver Pit, OSP), the other with high tidal disturbance but lower trawling disturbance (Thames). There was no measurable impact of trawling activity on oxygen uptake, denitrification or nutrient exchange in either region. In contrast, at the high trawling disturbance sites in the OSP only, there was both a shift in particle size distribution (towards fines) and a greater rate of sulphate reduction (volume specific rates 0.83 and 0.49 nmol SO4 2- cm -3 h -1 at high and low impact sites, respectively), but not in the Thames. In addi- tion, areal rates of sulphate reduction were positively correlated with both silt content (i.e. associated with organics) and long-term trawling in the OSP but not in the Thames. Biogeochemical processes in the upper layers of sediment, both oxic and suboxic, seemed unaffected by trawling in the long- term. In deeper anoxic sediment, however, mineralisation via sulphate reduction may be stimulated by the extra disturbance, at least in areas where tidal energy is slight.

Epilithic boulder communities of Lough Hyne, Ireland: the influences of water movement and sediment

The Marine Nature Reserve of Lough Hyne (south-west Ireland) encompasses an extremely wide range of marine conditions within a small area. A total of 378 boulders were collected from a range of depths at five sites subjected to very different degrees of water movement and sedimentation. Encrusting biota were identified and the communities compared between sites and upper and lower surfaces. In all, 114 taxa were identified. Alpha diversity was generally found to be higher for lower surfaces at sites with intermediate flow/disturbance. Sites with high water flow had much greater space occupation, predominantly cheilostomatid bryozoans. Multivariate analyses divided the samples into six groupings. Similarity percentage analysis (SIMPER) was used to indicate particular species characteristic of each group. Equations for the species-area curves generated tended to indicate communities at equilibrium except at sites subjected to stresses such as high sediment load or high disturbance. For high disturbance sites it was apparent that number of species cm−2 was significantly negatively correlated with surface area of rock implying non-random distribution.

Community attributes of atlantic white cedar (Chamaecyparis thyoides) swamps in disturbed and undisturbed Pinelands watersheds

We assessed the effect of regional watershed conditions on plant community attributes, scedbed and seedling density, and environmental conditions in New Jersey Pinelands Atlantic white cedar (Chamaecyparis thyoides) swamps under three disturbance regimes (high, moderate, and low). High regional watershed disturbance, defined by the percentage basin cover of combined residential and agricultural development, was associated with elevated pH, specific conductance, and nutrient concentrations in surface waters adjacent to our study sites. High disturbance sites generally had lower understory species richness and differed from other sites in overall understory species composition. High canopy red maple (Acer rubrum) cover and high canopy closure were also associated with swamps in high disturbance basins. Because other environmental variables did not differ significantly between disturbance types and red maple is a common associate, of cedar throughout the Pinelands, differences in species richness and composition may be related to canopy conditions rather than the effects of watershed disturbance. Regional differences in biogeography may also be a factor. We found no exotic species in our study sites. Only one species considered uncharacteristic of the Pinelands was associated with high disturbance basin sites. Unlike previous, similar studies in the Pinelands, the high disturbance sites did not support a unique group of plants. AlthoughSphagnum cover (typically, associated with optimal cedar seedbed conditions) was lowest in disturbed basin sites, there were no significant differences in overall seedbed conditions and cedar seedling density. Cedar swamps located a distance from upgradient watershed disturbances and not affected by overbank flooding seem to be buffered from the impacts of these regional disturbances.

The Effects of Habitat Fragmentation and Livestock-Grazing on Animal Communities in Remnants of Gimlet Eucalyptus salubris Woodland in the Western Australian Wheatbelt. I. Arthropods

The effects of habitat fragmentation (remnant biogeographic characteristics) and livestock activity (grazing, trampling) on arthropod communities were examined within 26 remnants of gimlet Eucalyptus salubris woodland in the central wheatbelt of Western Australia. Significant correlations between remnant biogeographic variables were between remnant area and connectivity (+ ve, P < 0001), and between connectivity and distance from the study remnant to the nearest patch of native vegetation (- ve, P < 0.001). Remnant disturbance indices (sheep faecal pellet density, percentage cover of weeds) were significantly correlated with remnant biogeographic characteristics (P < 0.01). Small and poorly connected remnants showed significantly higher intensities of disturbance than larger and better connected remnants. When disturbance indices were used to categorize study remnants into groups with high, moderate or low disturbance, remnants with high intensities of disturbance had significantly less lichen, litter and shrub cover. Highly disturbed remnants were associated with : fewer scorpion species, lower termite and ant diversity (Shannon-Wiener); a lower abundance of scorpions, termites and mygalomorph spiders; more beetle species and higher beetle diversity, and greater abundance of earwigs and beetles. Cockroach, earwig and ant species richness showed no significant response to disturbance. Species richness of termites, and the abundance of lycosid and idiopid (mygalomorph) spiders, isopods, cockroaches and ants, was highest under moderate disturbance. Significant biogeographic covariates were area (abundance of araneaomorph spiders, 'associated subordinate' and 'opportunistic' ants; richness of carabid, scarabid and 'other' beetle species, subordinate and opportunistic ants), connectivity (richness of termites, scarabid beetles) and distance to the nearest native vegetation (richness of 'dominant' ants). When disturbance and biogeographic effects were combined, total termite richness, and the richness of termite functional groups, declined markedly in highly disturbed, small and poorly connected remnants. Termite communities in relatively undisturbed remnants were more similar in species composition to communities in moderately disturbed quadrats than to communities in highly disturbed quadrats. Community similarity values for ants and beetles were similar across the study quadrats with different degrees of disturbance. Arthropod communities were also examined by canonical variate analyses across remnants with different degrees of disturbance, using total abundance and richness, and abundance and richness of predators (scorpions, spiders, carabid beetles, ants) and detritivores/herbivores (termites, isopods, earwigs, cockroaches, weevil and scarab beetles). Effective site separation into the three disturbance categories was found for abundance and richness of all arthropods, and for predators alone. Abundance and richness of detritivores/herbivores separated into two groups of sites: high disturbance sites, and sites with low or moderate disturbance with no separation. In stepwise regression analyses, lichen cover, weed cover and sheep faecal pellet density were the most significant indicators of faunal abundance, richness and diversity. Remnant biogeographic variables explained a low percentage of variation in faunal characteristics. Habitat disturbance was the major influence on the arthropod communities, with remnant biogeographic factors consistently explaining low variations in the abundance or diversity of the fauna. The implications of our findings for the management of remnant vegetation are discussed.