Effects Of Habitat Modification Research Articles

Community assembly of comammox Nitrospira in coastal wetlands across southeastern China.

Complete ammonia oxidizers (comammox Nitrospira) are ubiquitous in coastal wetland sediments and play an important role in nitrification. Our study examined the impact of habitat modifications on comammox Nitrospira communities in coastal wetland sediments across tropical and subtropical regions of southeastern China. Samples were collected from 21 coastal wetlands in five provinces where native mudflats were invaded by Spartina alterniflora and subsequently converted to aquaculture ponds. The results showed that comammox Nitrospira abundances were mainly influenced by sediment grain size rather than by habitat modifications. Compared to S. alterniflora marshes and native mudflats, aquaculture pond sediments had lower comammox Nitrospira diversity, lower clade A.1 abundance, and higher clade A.2 abundance. Sulfate concentration was the most important factor controlling the diversity of comammox Nitrospira. The response of comammox Nitrospira community to habitat change varied significantly by location, and environmental variables accounted for only 11.2% of the variations in community structure across all sites. In all three habitat types, dispersal limitation largely controlled the comammox Nitrospira community assembly process, indicating the stochastic nature of these sediment communities in coastal wetlands. IMPORTANCE Comammox Nitrospira have recently gained attention for their potential role in nitrification and nitrous oxide (N2O) emissions in soil and sediment. However, their distribution and assembly in impacted coastal wetland are poorly understood, particularly on a large spatial scale. Our study provides novel evidence that the effects of habitat modification on comammox Nitrospira communities are dependent on the location of the wetland. We also found that the assembly of comammox Nitrospira communities in coastal wetlands was mainly governed by stochastic processes. Nevertheless, sediment grain size and sulfate concentration were identified as key variables affecting comammox Nitrospira abundance and diversity in coastal sediments. These findings are significant as they advance our understanding of the environmental adaptation of comammox Nitrospira and how future landscape modifications may impact their abundance and diversity in coastal wetlands.

Habitat alteration facilitates the dominance of invasive species through disrupting niche partitioning in floodplain wetlands

AbstractAimExotic species invasion often leads to declines in local and regional biodiversity, particularly in freshwater ecosystems. This biodiversity loss is generally facilitated by human activities such as land cover change and hydrological alternation. Recent advances in stable isotope analysis (SIA) have been highlighted in many studies addressing fundamental issues in invasion ecology, especially in quantifying competition for resources between native and exotic species. However, how anthropogenic disturbance influences trophic relationships among invasive and native species remains poorly understood.LocationMiddle‐lower Yangtze River Region, China.MethodsTo investigate the effects of human disturbance on interspecific trophic interactions, this study compared isotopic niche space and overlap of the introduced red swamp crayfish (Procambarus clarkii) and the native oriental river shrimp (Macrobrachium nipponense) and freshwater snail (Bellamya aeruginosa) in natural and modified wetlands.ResultsBased on carbon and nitrogen SIA, we found ubiquitous niche shifts in macroinvertebrates with increased competition, which might lead to significant niche contraction in modified habitats at both community and population scales. Moreover, the isotopic niche width of the exotic crayfish was twice as larger as that of natives at both habitats, suggesting that the exotic P. clarkii had great competitive superiority over the native species. However, the effects of habitat modification on niche overlap were inconsistent. While the niche overlap between crayfish and shrimp was significantly higher in modified habitats than in natural open waters, niche overlap between crayfish and the snail was significantly reduced.Main conclusionsCollectively, our findings highlight that the competitive outcomes of interspecific trophic interactions can be dependent on the prey availability and diversity, which embraces both the classic optimal foraging theory and competition theory to understand how environmental change, such as habitat alternation, affects the biological invasion processes.

Effects of habitat modifications on the movement behavior of animals: the case study of Fish Aggregating Devices (FADs) and tropical tunas

BackgroundAggregation sites represent important sources of environmental heterogeneity and can modify the movement behavior of animals. When these sites are artificially established through anthropogenic actions, the consequent alterations to animal movements may impact their ecology with potential implications for their fitness. Floating objects represent important sources of habitat heterogeneity for tropical tunas, beneath which these species naturally aggregate in large numbers. Man-made floating objects, called Fish Aggregating Devices (FAD), are used by fishers on a massive scale to facilitate fishing operations. In addition to the direct impacts that fishing with FADs has on tuna populations, assessing the effects of increasing the numbers of FADs on the ecology of tuna is key for generating sound management and conservation measures.MethodsThis study investigates the effects of increasing numbers of FADs (aggregation sites) on the movements of tunas, through the comparison of electronic tagging data recorded from 146 individuals tunas (yellowfin tuna, Thunnus albacares, and skipjack tuna, Katsuwonus pelamis) tagged in three instrumented anchored FAD arrays (Mauritius, Oahu-Hawaii and Maldives), that differed according to their distances among neighboring FADs. The effect of increasing inter-FAD distances is studied considering a set of indices (residence times at FADs and absence (travel) times between two visits at FADs) and their trends.ResultsWhen inter-FAD distances decrease, tuna visit more FADs (higher connectivity between FADs), spend less time travelling between FADs and more time associated with them. The trends observed for the absence (travel) times appear to be compatible with a random-search component in the movement behaviour of tunas. Conversely, FAD residence times showed opposite trends, which could be a result of social behavior and/or prey availability.ConclusionOur results provide the first evidence of changes in tuna associative behavior for increasing FAD densities. More generally, they highlight the need for comparing animal movements in heterogeneous habitats in order to improve understanding of the impacts of anthropogenic habitat modifications on the ecology of wild animals.

Influence of the edge-core gradient on the scorpion assemblage (Arachnida, Scorpiones) in a Brazilian Atlantic forest

Habitat structure plays a major role in the distribution of species in a given area. Edge-core gradients may be useful for examining the effects of habitat modifications, as they represent changes in habitat structure at a small spatial scale. Here, we analyzed how scorpion assemblages were affected by variations in habitat structure along an edge-core gradient in a Brazilian Atlantic forest fragment. Scorpions were collected during 20 months (May 2007 – December 2008) in 112 pitfall traps, arranged from the fragment edge to 500 m inside the forest interior. All pitfall traps were checked in each two days with all scorpions found being collected. We also measured eight environmental variables along the edge-core gradient: canopy cover, leaf litter depth, diameter at breast height (DBH), plus the densities of fallen logs, stones, trees, shrubs, and bromeliads. We collected a total of 767 scorpions, all within the Buthidae family, and five species were identified (Ananteris mauryi, Tityus brazilae, T. neglectus, T. pusillus, and T. stigmurus). The abundance of these arachnids was positively influenced by habitat structure, with more individuals occurring in areas with trees having higher DBH values. However, species richness and composition were not affected by any of the environmental variables. Our results suggest that, at small spatial scales, scorpion assemblage (i.e. abundance) is sensitive to changes in habitat structure. Here, we have highlighted the importance of habitat structure for the maintenance of scorpion assemblages in their habitats.

Growth Performance and Adaptive Strategy of Early Seedlings of Three Savanna Woody Species in Pots as Feedback to the Soil of Macrotermes Subhyalinus Mound

Heterogeneous physiognomy and observed diversity of woody vegetation in savanna are considered as specific responses of seedling species during their growth to the given site characteristics changeable with time. Consequently, understanding early plant attitude using different growth soil is an important indicator in choosing species to introduce or to assist natural or artificial regeneration to the extent that establishment and productivity of plant species are not solely controlled by the effects of habitat modification and/or environmental resource availability but mostly by seedling quality. This study focused on comparative assessment of growth performance and adaptive traits of early seedlings of Balanites aegyptiaca, Diospyros mespiliformis and Tamarindus indica three multipurpose species between of Macrotermes subhyalinus mound and surrounding area in order to understand the attitudes of woody species hosted by termite mounds. Seedlings of similar age per species were grown in plastic bags as pots containing composite soils sampled till a depth of 30 cm on mounds and surrounding area in Tiogo state forest and of which the amount of retained water, carbon (C), nitrogen (N), calcium (Ca), magnesium (Mg), assimilable phosphorus (ass. P) and potassium (K) were quantified prior to growth experiment. Height and collar diameter of seedling stems, final length and diameter of the main root were measured; the total dry biomass of root and shoot and, root to shoot ratio were evaluated for seedlings up to 5 months relating to the soil origin. Mean values of retained water and selected nutrients were higher for mound soil than for surrounding soil. Besides, the studied parameters of T. indica seedlings were significantly higher for mound soil than those recorded for surrounding soil (P<0.05) whereas seedlings of B. aegyptiaca and D. mespiliformis exhibited an increase final stem collar diameter and main root length on mound soil (P=0.039 and 0.028 respectively). Root to shoot ratio of B. aegyptiaca seedlings was positively correlated with great N content and that of D. mespiliformis seedlings with great concentration of Ca. Growth performance and adaptive traits of early seedlings of B. aegyptiaca, D. mespiliformis and T. indica were remarkable on M. subhyalinus mound soil compared to surrounding soil relating to the great level ofsoil fertility. Therefore, understanding the attitude of woody seedlings of local or exotic species is an important key in global plantation programs or assisting natural regeneration for biodiversity management and conservation.

Potential effect of habitat disturbance on reproduction of the critically endangered harlequin frog Atelopus varius in Las Tablas, Costa Rica

We studied a population of Atelopus varius in Las Tablas Protected Zone in southwest Costa Rica, where we estimated occupancy rates of tadpoles along the Cotón River. In addition, we report the first tadpoles observed in the wild in 20 years. Tadpole rate of occupancy was greater in habitat containing native forest than in disturbed areas bordering cattle pasture. This same pattern was also reflected in adult hotspots, where encounter rates were higher for adults in habitat surrounded by forest versus pasture. We present evidence for the potential effect of habitat modification on the presence and reproduction of A. varius and suspect that over time this modification impacts the species’ demography. However, further study is necessary before we can confirm that habitat change alone was the key factor involved in patterns of decline for the species.

Effects of habitat modification on cotton rat population dynamics and rodent community structure

Concerns over climate change and finite fossil fuels have generated interest in biofuels. Switchgrass (Panicum virgatum), a biofuel feedstock, was planted in intensively managed loblolly pine (Pinus taeda) stands to investigate sustainability of this system for producing an alternative energy source. We hypothesized that changes in understory habitat conditions caused by intercropping switchgrass in pine stands would affect rodent population and community dynamics within three years. Therefore, we assessed effects of three treatments (control pine, switchgrass intercropped in pine, and switchgrass monocrop) on rodent population (abundance, survival, and recruitment) and community (diversity, richness, evenness, and community assemblages) measures. We conducted vegetation surveys and live-trapping during 2013–2015 summers in Kemper County, Mississippi, USA. We conducted 6 trapping sessions each summer (n=14,112 trap nights per year) and captured 1,733 cotton rats (Sigmodon hispidus), 102 Oryzomys palustris, 31 Mus musculus, 28 Reithrodontomys fulvescens, 22 Reithrodontomys humulis, 20 Peromyscus leucopus, 9 Microtus pinetorum, 9 Peromyscus gossypinus, and 2 Neotoma floridana. We found greater cotton rat abundance and lower recruitment in monocrop versus control plots. Rodent diversity was lower in monocrop than control plots. Intercropped plots had intermediate levels of cotton rat abundance and recruitment, and rodent diversity. More dispersal may have occurred in monocrop plots because of high population abundance and limited habitat availability. Cotton rat survival and rodent community assemblage were similar among treatments but differed among years. Although rodents responded negatively to monocrop plots, our results suggested intercropped plots would be an appropriate management practice in pine plantations to produce biofuel feedstocks while maintaining rodent diversity.

Ecosystem engineering by a gall‐forming wasp indirectly suppresses diversity and density of herbivores on oak trees

Ecosystem engineers, organisms that modify the physical environment, are generally thought to increase diversity by facilitating species that benefit from engineered habitats. Recent theoretical work, however, suggests that ecosystem engineering could initiate cascades of trophic interactions that shape community structure in unexpected ways, potentially having negative indirect effects on abundance and diversity in components of the community that do not directly interact with the habitat modifications. We tested the indirect effects of a gall-forming wasp on arthropod communities in surrounding unmodified foliage. We experimentally removed all senesced galls from entire trees during winter and sampled the arthropod community on foliage after budburst. Gall removal resulted in 59% greater herbivore density, 26% greater herbivore richness, and 27% greater arthropod density five weeks after budburst. Gall removal also reduced the differences in community composition among trees (i.e., reduced beta diversity), even when accounting for differences in richness. The community inside galls during winter and through the growing season was dominated by jumping spiders (Salticidae; 0.87 ± 0.12 spiders per gall). We suggest that senesced galls provided habitat for spiders, which suppressed herbivorous arthropods and increased beta diversity by facilitating assembly of unusual arthropod communities. Our results demonstrate that the effects of habitat modification by ecosystem engineers can extend beyond merely providing habitat for specialists; the effects can propagate far enough to influence the structure of communities that do not directly interact with habitat modifications.

Effect of Habitat Modifications on Predation Potential of &lt;i&gt;Anisops sardea&lt;/i&gt; (Hemiptera: Notonectidae) against Larvae of Culex vishnui, Vector of Japanease Encephalitis

To prevent emergence of insecticide resistance in vector population & biological magnification of toxic insecticides through food chain, more attention is now put on application of biological control system to reduce the population of vectors. Present study was carried out to assess the effect of habitat modifications on the predatory ability of Anisops sardea (Hemiptera: Notonectidae) against immature of Culex Vishnui (Diptera: Culicidae) group of mosquitoes in laboratory and semi-field bioassay.To study the effect of habitat modifications, laboratory based predatory experiments were carried with A. sardea as predator and Cx.vishnui group of mosquitoes as prey species. To determine prey preference of predator species, predatory experiment was done in presence of mosquitoes belongs to different genera. For a long-term study on predation rate, for 15 consecutive days, 10 adult individuals of A. sardea were kept in a plastic bucket of 20 L capacity in open natural condition and number of mosquito larvae consumed/per day was calculated.Result of single factor ANOVA analysis revealed that habitat modifications have significant effect on the predatory rate of A sardea as calculated F value (34.10) is significantly higher than table value (F crit =2.156). Pair wise ‘t test’ revealed significant variations in the predation rate when different habitat combinations were analyzed. Results of selectivity index, niche breadth and food breadth were also evaluated. Long term bioassay in semi-field condition revealed that predatory rates were almost similar throughout the study period.Considering the habitat specificity, prey preference and the rate of predation in semi field condition, it can be concluded that A. sardea can be used as potential biological control agent against Culex Vishnui group of mosquitoes.

Climate and land-use changes effects on the distribution of a regional endemism: Melanophryniscus sanmartini (Amphibia, Bufonidae)

ABSTRACT Amphibians are the most threatened vertebrate group according to the IUCN. Land-use and land cover change (LULCC) and climate change (CC) are two of the main factors related to declining amphibian populations. Given the vulnerability of threatened and rare species, the study of their response to these impacts is a conservation priority. The aim of this work was to analyze the combined impact of LULCC and CC on the regionally endemic species Melanophryniscus sanmartini Klappenbach, 1968. This species is currently categorized as near threatened by the IUCN, and previous studies suggest negative effects of projected changes in climate. Using maximum entropy methods we modeled the effects of CC on the current and mid-century distribution of M. sanmartini under two IPCC scenarios - A2 (severe) and B2 (moderate). The effects of LULCC were studied by superimposing the potential distribution with current land use, while future distribution models were evaluated under the scenario of maximum expansion of soybean and afforestation in Uruguay. The results suggest that M. sanmartini is distributed in eastern Uruguay and the south of Brazil, mainly related to hilly and grasslands systems. Currently more than 10% of this species' distribution is superimposed by agricultural crops and exotic forest plantations. Contrasting with a recent modelling study our models suggest an expansion of the distribution of M. sanmartini by mid-century under both climate scenarios. However, despite the rise in climatically suitable areas for the species in the future, LULCC projections indicate that the proportion of modified habitats will occupy up to 25% of the distribution of M. sanmartini. Future change in climate conditions could represent an opportunity for M. sanmartini, but management measures are needed to mitigate the effects of habitat modification in order to ensure its survival and allow the eventual expansion of its distribution.

Anthropogenic modification disrupts species co‐occurrence in stream invertebrates

The question of whether species co-occurrence is random or deterministic has received considerable attention, but little is known about how anthropogenic disturbance mediates the outcomes. By combining experiments, field surveys and analysis against null models, we tested the hypothesis that anthropogenic habitat modification disrupts species co-occurrence in stream invertebrates across spatial scales. Whereas communities in unmodified conditions were structured deterministically with significant species segregation, catchment-scale conversion to agriculture and sediment deposition at the patch- or micro-habitat scale apparently randomized species co-occurrences. This shift from non-random to random was mostly independent of species richness, abundance and spatial scale. Data on community-wide life-history traits (body size, dispersal ability and predatory habits) and beta-diversity indicated that anthropogenic modification disrupted community assembly by affecting biotic interactions and, to a lesser extent, altering habitat heterogeneity. These data illustrate that the balance between predictable and stochastic patterns in communities can reflect anthropogenic modifications that not only transcend scales but also change the relative forces that determine species coexistence. Research into the effects of habitat modification as a key to understanding global change should extend beyond species richness and composition to include species co-occurrence, species interactions and any functional consequences.

Patch shape alters spider community structure: links between microhabitat choice and sensitivity to increased edge habitat

Increased edge effects in fragmented habitats can affect the abundance of edge-dwelling organisms, but these impacts may depend on the biological attributes of species. Microhabitat choice, a species characteristic that reflects combinations of biological traits, may affect the ability of peripheral species to take advantage of increased edge habitat in the presence of edge effects. In this field study, we built artificial shrub modules designed to encourage web spiders to build webs on the periphery. While modules were identical in volume, they differed in shape (cubic and elongated), so that elongated modules had more edge habitat and were subject to enhanced edge effects. Given that the tangle-web spiders Theridion and Dictyna built webs on module edges and strongly differed in terms of concealment and substrate generalization, two habitat characteristics associated with lower vulnerability to habitat modification, we tested the hypothesis that Theridion, which built webs in more concealed locations and on a greater diversity of substrate configurations in the modules compared to Dictyna, would take better advantage of increased edge habitat. As predicted, Theridion was significantly more abundant on elongated modules whereas the abundance of Dictyna did not respond to shape, even though the change in module shape entailed a similar increase in favored substrate for both spider groups. Our results suggest that the microhabitat associations of organisms may be linked to their propensity to be sensitive to edges, and that a better understanding of these links can improve our ability to predict the effects of habitat modification on biodiversity.

Effects of habitat modification on coastal fish assemblages

The purpose of this study was to assess the influence of anthropogenic modification of coastal habitats on fish assemblages in Taiwan, comparing the abundance, species richness and taxonomic composition of fishes on natural v. artificial habitats. While there was no significant variation in the abundance or richness of fishes between natural and artificial habitats, the species composition of fishes in artificial habitats was significantly different from that of natural habitats. Natural reefs were characterized by greater abundance of Stethojulis spp. (Labridae), Abudefduf spp. (Pomacentridae) and Thalassoma spp. (Labridae), whereas anthropogenic habitats were dominated by Parupeneus indicus (Mullidae), Pempheris oualensis (Pempheridae) and Parapriacanthus ransonneti (Pempheridae). In general, it appears that specialist reef-associated species are being replaced with fishes that are much more generalist in their habitat-use. The loss of natural coastal habitats may threaten some species that cannot live in anthropogenically altered habitats, though the overall abundance and diversity of coastal fishes was not significantly different between natural and artificial habitats in Taiwan.

Impacts of Active Oil Pumps and Deer Feed Plots on Amphibian and Reptile Assemblages in a Floodplain

Abstract Floodplain forests are among the most threatened habitats in North America. We used the richness, abundance and diversity of amphibians and reptiles to assess the effects of habitat modifications at the Old Sabine Bottom Wildlife Management Area (OSBWMA) in Smith County, Texas, USA. Amphibians and reptiles were surveyed using artificial cover objects and minnow traps at nine ephemeral pools: three in undisturbed bottomland forest, three in deer food plots and three near active oil pumps. A total of 627 amphibians and reptiles representing 31 species was captured. Undisturbed forest plots sustained a higher amphibian richness compared to food and oil pump plots. Amphibian abundance differed significantly among habitats with food plots having the highest and oil pump plots the lowest. Reptile abundance was not significantly different among habitat types neither was reptile richness following rarefaction correction. Overall, each habitat type had similar Simpson's diversity indices, ranging from 0.8...

A national framework for research on trophic regulation by the Dingo in Australia

There is increasing evidence that the Dingo Canis lupus dingo plays an important ecological role as a trophic regulator in Australian ecosystems. However, there is sufficient remaining uncertainty about the nature of this role as to hinder the development of effective management policies. This review defines strategic directions for future research on the trophic role of Dingoes by developing a national Dingo research framework. The framework aims to increase our knowledge of the influence that Dingoes have on the maintenance of biodiversity, thereby encouraging Dingo conservation and the refinement of current land-use practices. The framework begins by identifying four major bioclimatic zones across Australia that pose different questions and challenges for Dingo research. For each zone we construct a model that identifies major interactions between Dingoes and key prey or competitor species, and then used the models to identify key research needs, the possible advantages of maintaining Dingo populations within each zone, and ways to tease out unstudied interactions. Important questions identified in the review include the effects of Dingoes on native marsupial populations, vegetation communities, herbivore diets, the use of structural refugia by mesopredators, predator and prey behaviour, and the effect of habitat modification on these interactions. We briefly review legislative constraints and other factors, such as the ongoing hybridization of Dingo populations with domestic dog breeds, that may impede future studies. If research activities follow this framework, we believe that policy and management will be better informed, benefiting both the Dingo and the natural ecosystems and production systems where it occurs.

Biomechanical warfare in ecology; negative interactions between species by habitat modification

Since the introduction of the term ecosystem engineering by Jones et al. many studies have focused on positive, facilitative interactions caused by ecosystem engineering. Much less emphasis has been placed on the role of ecosystem engineering in causing negative interactions between species. Here, we report on negative interactions between two well known ecosystem engineers occurring at the interface of salt marsh and intertidal flat (i.e. common cordgrass Spartina anglica and lugworms Arenicola marina), via modification of their joint habitat. A field survey indicated that, although both species share a common habitat, they rarely co-occur on small spatial scales (<1 m). Experiments in the field and in mesocosms reveal that establishment of small Spartina plants is inhibited in Arenicola-dominated patches because of low sediment stability induced by the lugworms. In turn, Arenicola establishment in Spartina-dominated patches is limited by high silt content, compactness and dense rooting of the sediment caused by Spartina presence. Our results show that negative interactions by modification of the environment can result in rapid mutual exclusion, particularly if adverse effects of habitat modification are strong and if both species exhibit positive feedbacks. This illustrates the potential for negative interactions via the environment to affect community composition.

Changes in size structure of macroinvertebrate assemblages with habitat modification by aggregations of caddisfly cases

AbstractWe conducted a field experiment to evaluate the effects of habitat modification by aggregations of the case-building caddisfly Goera japonica Banks (Trichoptera:Goeridae) on the size structure and composition of benthic macroinvertebrate assemblages in a Japanese stream. We compared macroinvertebrate assemblages between cobbles with (intact treatment) and without (removal treatment) case aggregations of G. japonica. The total biomass of macroinvertebrates and Margalef’s index did not differ between the treatments, but total abundance and taxon richness were higher in the intact treatment than in the removal treatment. Mean body length of macroinvertebrates was significantly smaller in the intact than in the removal treatment. Abundance of individuals in small ( 3.00 mm) size class did not differ between treatments. For 5 of the 9 ...

DIVERSITY, ECOSYSTEM FUNCTION, AND STABILITY OF PARASITOID–HOST INTERACTIONS ACROSS A TROPICAL HABITAT GRADIENT

Global biodiversity decline has prompted great interest in the effects of habitat modification and diversity on the functioning and stability of ecosystem processes. However, the applicability of previous modeled or mesocosm community studies to real diverse communities in different habitats remains ambiguous. We exposed standardized nesting resources for naturally occurring communities of cavity-nesting bees and wasps and their parasitoids in coastal Ecuador, to test the effects of host and parasitoid diversity on an ecosystem function (parasitism rates) and temporal variability in this function. In accordance with predictions of complementary host use, parasitism rates increased with increasing diversity, not simply abundance, of parasitoids. In contrast, parasitism decreased with increasing host diversity, possibly due to positive prey interactions or increased probability of selecting unpalatable species. Temporal variability in parasitism was lower in plots with high mean parasitoid diversity and higher in plots with temporally variable host and parasitoid diversity. These effects of diversity on parasitism and temporal stability in parasitism rates were sufficiently strong to be visible across five different habitat types, representing a gradient of increasing anthropogenic modification. Habitat type did not directly affect parasitism rates, but host and parasitoid diversity and abundance were higher in highly modified habitats, and parasitoid diversity was positively correlated with rates of parasitism. The slope of the richness-parasitism relationship did not vary significantly across habitats, although that for Simpson's diversity was significant only in rice and pasture. We also show that pooling data over long time periods, as in previous studies, can blur the effect of diversity on parasitism rates, and the appropriate spatiotemporal scale of study must be considered.

Success of intracoelomic radiotransmitter implantation in the treefrog (Hyla versicolor)

Concern about the effects of habitat modification on the natural movements and behavior of amphibians has led researchers to devise several methods to follow individual animals as they migrate among seasonal resources; one such method is the surgical insertion of radiotransmitters. Intracoelomic implantation has come into general use despite the relative lack of specific procedural guidelines and information about the effects of transmitter insertion and removal. The author outlines the surgical implantation procedures used on a small amphibian (gray treefrog) and provides insight into the effects of multiple major surgical invasions on the long-term survival of amphibians. Multiple survival surgeries were successful in this study and may be an alternative to euthanasia in some instances.

Consolidation and volumetric soil-water content of salt marsh soils following habitat modification for mosquito control

The runnelling form of habitat modification for mosquito control in saltmarsh increases tidal frequency, and may affect soil properties such as volumetric soil-water content and consolidation. The effects of habitat modification on soil properties are in turn likely to affect ecological processes. Runnels constructed mechanically to a depth of no more than 0.3 m with smooth, spoon shaped edges linked isolated mosquito-breeding pools in the high marsh to the tidal source at the saltmarsh/mangrove interface. The physical design of runnels may result in a significant increase in the frequency of flooding tidal events that flush isolated mosquito-breeding pools. Impacts of the runnelling technique were determined at three marshes using two sampling protocols: (a) comparisons between modified and unmodified shores and (b) comparisons with lateral distance from a runnel. At one marsh, volumetric water content was significantly higher at runnelled than at unrunnelled sites after tides that only partly inundated the marsh, but this pattern was not found at the other marshes. Soil consolidation was greater further from the shore, but was not different between runnelled and unrunnelled shores. Measurements at different lateral distances from runnels demonstrated higher water content levels and lower consolidation up to 5 m from runnels and no effect further away. The varied responses to runnelling at different marshes may reflect specific site characteristics such as slope and hydraulic tidal forces. Remedial strategies for similar mosquito control techniques, based on habitat modification, should include dynamic classifications of saltmarshes.