Spatial Distribution Abundance Research Articles

Trawl exposure and protection of seabed fauna at large spatial scales

AbstractAimTrawling is the most widespread direct human disturbance on the seabed. Knowledge of the extent and consequences of this disturbance is limited because large‐scale distributions of seabed fauna are not well known. We map faunal distributions in the Australian Exclusive Economic Zone (EEZ) and quantify the proportion of their abundance that occurs in areas 1) that are directly trawled and 2) where legislation permanently prohibits trawling—defined as percentage exposure or protection, respectively. Our approach includes developing a method that integrates data from disparate seabed surveys to spatially expand predicted benthos distributions.LocationAustralia.MethodsWe collate data from 18 seabed surveys to map the distribution of seabed invertebrates (benthos) in nine regions. Our approach combines data from multiple surveys, groups taxa within taxonomic classes and uses Random Forests to predict spatial abundance distributions of benthos groups from environmental variables. Exposure and protection of benthos groups were quantified by mapping their predicted abundance distributions against the footprint of trawling and legislated boundaries of marine reserves and fishery closures.ResultsTrawling is currently prohibited from more area of Australia's EEZ (58%) than is trawled (<5%). Across 134 benthos groups, 96% had greater protection of abundance than exposure. The mean trawl exposure of benthos‐group abundance was 7%, compared to mean protection of 38%, whereas the mean abundance neither trawled nor protected was 55%. Fishery closures covered 19% less study area than marine reserves, but overlapped with a higher proportion (5% more) of benthos‐group abundance.Main ConclusionsThis study provides the most extensive quantitative assessment of the current exposure of Australia's benthos to trawling. Further, it highlights the contribution of fishery closures to marine conservation. These results help identify regions and taxa that are at greatest potential risk from trawling and support managers to achieve balance between conservation and sustainable industries in marine ecosystems.

Spatial Distribution of Element Abundances and Ionization States in Solar Energetic-Particle Events

We have studied the spatial and temporal distribution of abundances of chemical elements in large "gradual" solar energetic-particle (SEP) events, and especially the source plasma temperatures, derived from those abundances, using measurements from the Wind and Solar TErestrial RElations Observatory (STEREO) spacecraft, widely separated in solar longitude. A power-law relationship between abundance enhancements and mass-to-charge ratios [A/Q] of the ions can be used to determine Q-values and source plasma temperatures at remote spacecraft with instruments that were not designed for charge-state measurements. We search for possible source variations along the accelerating shock wave, finding one clear case where the accelerating shock wave appears to dispatch ions from 3.2+-0.8 MK plasma toward one spacecraft and those from 1.6+-0.2 MK plasma toward another, 116 deg away. The difference persists three days and then fades away. Three other SEP events show less-extreme variation in source temperatures at different spacecraft, in one case observed over 222 deg in longitude. This initial study shows how the power-law relation between abundance enhancements and ion A/Q-values pro-vides a new technique to determine Q and plasma temperatures in the seed population of SEP ions over a broad region of space using remote spacecraft with instruments that were not originally designed for measurements of ionization states.

TheGaia-ESO Survey: radial distribution of abundances in the Galactic disc from open clusters and young-field stars

The spatial distribution of elemental abundances in the disc of our Galaxy gives insights both on its assembly process and subsequent evolution, and on the stellar nucleogenesis of the different elements. Gradients can be traced using several types of objects as, for instance, (young and old) stars, open clusters, HII regions, planetary nebulae. We aim at tracing the radial distributions of abundances of elements produced through different nucleosynthetic channels -the alpha-elements O, Mg, Si, Ca and Ti, and the iron-peak elements Fe, Cr, Ni and Sc - by using the Gaia-ESO idr4 results of open clusters and young field stars. From the UVES spectra of member stars, we determine the average composition of clusters with ages >0.1 Gyr. We derive statistical ages and distances of field stars. We trace the abundance gradients using the cluster and field populations and we compare them with a chemo-dynamical Galactic evolutionary model. Results. The adopted chemo-dynamical model, with the new generation of metallicity-dependent stellar yields for massive stars, is able to reproduce the observed spatial distributions of abundance ratios, in particular the abundance ratios of [O/Fe] and [Mg/Fe] in the inner disc (5 kpc<RGC <7 kpc), with their differences, that were usually poorly explained by chemical evolution models. Often, oxygen and magnesium are considered as equivalent in tracing alpha-element abundances and in deducing, e.g., the formation time-scales of different Galactic stellar populations. In addition, often [alpha/Fe] is computed combining several alpha-elements. Our results indicate, as expected, a complex and diverse nucleosynthesis of the various alpha-elements, in particular in the high metallicity regimes, pointing towards a different origin of these elements and highlighting the risk of considering them as a single class with common features.

Spatial pattern and cover effect on the abundance of a currently obliterated population of Melocactus violaceus: a threatened species in Brazilian sandy coastal plain

Environmental factors generally exhibit non-random patterns, and the spatial distribution of a species should, ideally, be translated into environmental patterns associated physiology and life-history constraints. This study was carried out in a habitat patch in Brazilian sandy coastal plain with occurrence of Melocactus violaceus subsp. margaritaceus. I investigated the spatial association between size classes and perennial plant cover from Spatial Analysis by Distance Index (SADIE) coupled with correlation analysis, in order to evaluate whether M.v. margaritaceus is associated with perennial plant cover. More-than-expected abundance was associated with bare ground for all size classes and less less-than-expected abundance in the patch of the perennial plants. The algorithm SADIE detected a significant clumped pattern in the spatial distribution of juveniles and adults abundance. Correlation analysis showed the presence of strong associations between size classes, except for cover which showed strong dissociations. Based on these analyses, I suggest that the establishment of this cactus species occurs preferably in bare ground or with little cover, and the spatial association is similar between size classes.

Distribusi Spasial Dan Struktur Komunitas Plankton Di Daerah Teluk Penerusan, Kabupaten Buleleng

Research spatial distribution and community structure of plankton in the Penerusan bay has been done on 22 February 2016.Plankton samples were taken at 17 stations using the Horizontal haul. The results obtained by the group of phytoplankton of the most widely found are from class Bacillariophyceae with the abundance of species composition percentage of 77% and the group most zooplankton were found came from class Maxillopoda with the percentage of the species composition of 85%. Highest abundance of phytoplankton found in abundance station 5, while the highest abundance of zooplankton found in abundance station 4. Index values diversity, uniformity and dominance of phytoplankton that is 1,06, 0.40 and 0.11 while the index value of diversity, uniformity and dominance zooplankton are 0.52,0.40 and 0.34. Results of the spatial distribution of phytoplankton abundance scattered in the middle of the bay towards the outside while the spatial distribution of zooplankton abundance spread from the south of the bay towards the middle of the bay and to the north of the bay Forwarding. Water quality in Penerusan Bay of physicists chemical parameters such as temperature obtained ranged from 31.1to 32,5 0C, average brightness obtained 87 %, turbidity obtained ranges between 0,73 to 2.62 ntu, dissolved oxygen (DO) obtained ranged from 6 to 8.3 mg/l , the degree of acidity (pH) obtained ranged from 7.17 to 8.04, salinity obtained ranged from 31-35 ppt, nitrate values obtained ranged from 0.60 to 1.83 mg/l and phosphate values obtained ranged from 0.10 to 0.78 mg/l.

Developing a two-step method for retrieving cyanobacteria abundance from inland eutrophic lakes using MERIS data

Cyanobacteria are the main dominant species in inland eutrophic lakes during algae blooms, and measures of cyanobacteria abundance can be used for monitoring and early detection of algal blooms by remote sensing. During May 2013 and August 2016, a total 137 water samples were collected from Lake Taihu and Lake Chaohu. Remote-sensing reflectance was measured, surface water was collected in the field, and chlorophyll-a concentration, phycocyanin concentration, suspended-matter concentration and phytoplankton pigment absorption parameters were measured in the laboratory. The composition and density of planktonic algae were also detected by microscope examination. The remote-sensing reflectance at 15 MERIS bands was simulated based on our measured spectral data, and a two-step method for detecting cyanobacteria abundance using the partial least squares model based on 5 MERIS bands was developed. The results showed that the estimation algorithm can predict cyanobacteria abundance in inland eutrophic lakes with satisfactory accuracy, with RMSE of 7.56 and MAPE of 13.44 %. This algorithm was successfully applied to the MERIS image acquired on August 12, 2010, and showed a reasonable spatial distribution of cyanobacteria abundance in Lake Taihu. It demonstrated that the developed estimation method was an effective way to monitor cyanobacteria abundance in water with a potential to be successfully applied to Sentinel-3 images.

Spectroscopic Observation and Analysis of H ii Regions in M33 with MMT: Temperatures and Oxygen Abundances

Abstract The spectra of 413 star-forming (or H ii) regions in M33 (NGC 598) were observed using the multifiber spectrograph of Hectospec at the 6.5 m Multiple Mirror Telescope. Using this homogeneous spectra sample, we measured the intensities of emission lines and some physical parameters, such as electron temperatures, electron densities, and metallicities. Oxygen abundances were derived via the direct method (when available) and two empirical strong-line methods, namely, O3N2 and N2. At the high-metallicity end, oxygen abundances derived from the O3N2 calibration were higher than those derived from the N2 index, indicating an inconsistency between O3N2 and N2 calibrations. We present a detailed analysis of the spatial distribution of gas-phase oxygen abundances in M33 and confirm the existence of the axisymmetric global metallicity distribution that is widely assumed in the literature. Local variations were also observed and subsequently associated with spiral structures to provide evidence of radial migration driven by arms. Our O/H gradient fitted out to 1.1 R 25 resulted in slopes of −0.17 ± 0.03, −0.19 ± 0.01, and −0.16 ± 0.17 dex , utilizing abundances from O3N2, N2 diagnostics, and a direct method, respectively.

Modeling the spatial distribution of larval fish abundance provides essential information for management

Productive fisheries are strongly linked to the ecological state of the essential habitats. In this study, we developed a methodology to assess the most important reproduction habitats of fish by using larval survey data and Bayesian species distribution models that predict the spatial distribution and abundance of fish larvae. Our case study with four commercially and ecologically important fish species in the coastal zone of the northern Baltic Sea demonstrated that the production of fish stocks can be concentrated to an extremely limited area compared with the entire suitable production area. The area suitable for larval production varied from 3.7% to 99.8% among species, but the smallest area responsible for 80% of the cumulative larval production was two to five times more limited, varying from 1.4% to 52.9% among species. Hence, instead of the traditional approach of modeling only habitat suitability for fish production, marine spatial planning and management should take into account the areal production potential. Moreover, the developed methodology enables linking of the total production potential across the whole distribution area to fisheries stock assessment and management.

Exploring the Ecological Coherence between the Spatial and Temporal Patterns of Bacterioplankton in Boreal Lakes.

One of the major contemporary challenges in microbial ecology has been to discriminate the reactive core from the random, unreactive components of bacterial communities. In previous work we used the spatial abundance distributions of bacterioplankton across boreal lakes of Québec to group taxa into four distinct categories that reflect either hydrology-mediated dispersal along the aquatic network or environmental selection mechanisms within lakes. Here, we test whether this categorization derived from the spatial distribution of taxa is maintained over time, by analyzing the temporal dynamics of the operational taxonomic units (OTUs) within those spatially derived categories along an annual cycle in the oligotrophic lake Croche (Québec, Canada), and assessing the coherence in the patterns of abundance, occurrence, and environmental range of these OTUs over space and time. We report that the temporal dynamics of most taxa within a single lake are largely coherent with those derived from their spatial distribution over large spatial scales, suggesting that these properties must be intrinsic of particular taxa. We also identified a set of rare taxa cataloged as having a random occupancy based on their spatial distribution, but which showed clear seasonality and abundance peaks along the year, yet these comprised a very small fraction of the total rare OTUs. We conclude that the presence of most rare bacterioplankton taxa in boreal lakes is random, since both their temporal and spatial dynamics suggest links to passive downstream transport and persistence in freshwater networks, rather than environmental selection.

A general framework for predicting delayed responses of ecological communities to habitat loss

Although biodiversity crisis at different spatial scales has been well recognised, the phenomena of extinction debt and immigration credit at a crossing-scale context are, at best, unclear. Based on two community patterns, regional species abundance distribution (SAD) and spatial abundance distribution (SAAD), Kitzes and Harte (2015) presented a macroecological framework for predicting post-disturbance delayed extinction patterns in the entire ecological community. In this study, we further expand this basic framework to predict diverse time-lagged effects of habitat destruction on local communities. Specifically, our generalisation of KH’s model could address the questions that could not be answered previously: (1) How many species are subjected to delayed extinction in a local community when habitat is destructed in other areas? (2) How do rare or endemic species contribute to extinction debt or immigration credit of the local community? (3) How will species differ between two local areas? From the demonstrations using two SAD models (single-parameter lognormal and logseries), the predicted patterns of the debt, credit, and change in the fraction of unique species can vary, but with consistencies and depending on several factors. The general framework deepens the understanding of the theoretical effects of habitat loss on community dynamic patterns in local samples.

Colonización y supervivencia de epibiontes sésiles en substratos artificiales similares a rizóforos de Rhizophora mangle (Rhizophoraceae) en La Mancha, México

La Mancha coastal lagoon, in the Gulf of Mexico, has an inlet that opens and closes seasonally, causing important fluctuations in flood-levels and exposing the intertidal zone to high solar radiation, high temperatures and desiccation. With the aim to examine the accumulated effect of variation in flood-levels on colonization and survival of sessile intertidal invertebrates on artificial substrates in a fringe mangrove forest, a field experiment was conducted from November-2000 to September-2001. A total of 72 PVC-stakes 2 m long were encased with cement to resemble rhizophores (prop roots) of Rhizophora mangle. They were then embedded in mud at four sampling stations (18 per station: 9 in a shaded site and 9 in a sunny site), and groups of 6 were collected from each sampling station (3 from each shaded site and 3 from each sunny site) without replacement at the end of each climatic period (nortes, dry and rainy). The open-closed condition of the inlet and the flood-level were monitored during different days throughout the 308-day experiment period. Temporal, spatial and vertical distribution of Species richness (S) and abundance of living and dead individuals were registered, and the data was analyzed by ANOVA. Only seven species colonized the substrates, the majority of them were recorded throughout the year and in all sampling stations. There was no seasonal succession of species. At the end of the experiment, only 20 % of the epibionts had survived. The polychaete Ficopomatus miamiensis was the most abundant, but had significantly lower survival than the other species (0–14 %). Epibionts preferred to settle in shaded sites rather than sunny ones regardless of the sampling station and the climatic season. In conclusion, artificial substrate colonization was successful but the majority of epibionts died because of long exposure and desiccation after the inlet was opened by local fishermen. Manual digging of the sand-barrier by local fishermen, disrupts the natural flooding cycles of the lagoon, and could severely impact the future development of mangrove communities.

SPICAand the Chemical Evolution of Galaxies: The Rise of Metals and Dust

AbstractThe physical processes driving the chemical evolution of galaxies in the last ~ 11Gyr cannot be understood without directly probing the dust-obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of the star formation and black hole accretion activity in galaxies at 1 &lt;z&lt; 3. Spectroscopic observations with a cryogenic infrared observatory likeSPICA, will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-infrared range in galaxies at high-z. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate howSPICAobservations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up toz~ 3, and the dust composition of galaxies at high-z. Possible synergies with facilities available in the late 2020s are also discussed.

Distribution Characteristics of Anaerobic Ammonia Oxidation Bacteria in Sediments from the Adjacent Seas of Yangtze Estuary

Marine nitrogen cycle is of great significance to maintain the marine ecological balance. Anaerobic ammonia oxidation (ANAMMOX) process driven by anaerobic ammonia-oxidizing bacteria is an important way of promoting the marine nitrogen removal. In this study, quantitative PCR (qPCR), combining with environmental factors analysis, were used to study the distribution of ANAMMOX bacteria in the sediments from Yangtze River Estuary and its adjacent waters in summer, 2011. The results showed that the spatial abundance distribution of ANAMMOX bacteria was closely related to environmental factors. Total organic carbon, salinity, and concentration of ammonium played vital roles in regulating ANAMMOX bacteria abundances in this area. The abundance distribution of ANAMMOX bacteria was significantly positively correlated with total organic carbon content (P<0.01,r=0.69), reducing along with the increasing concentration of nitrite and DO, while the influence from salinity was complicated.

Combined effects of urbanization and connectivity on iconic coastal fishes

AbstractAimDisturbance and connectivity shape the structure and spatial distribution of animal populations in all ecosystems, but the combined effects of these factors are rarely measured in coastal seascapes. We used surf zones of exposed sandy beaches in eastern Australia as a model seascape to test for combined effects of coastal urbanization and seascape connectivity (i.e. spatial links between surf zones, estuaries and rocky headlands) on fish assemblages.LocationFour hundred kilometres of exposed surf beaches along the eastern coastline of Australia.MethodsFish assemblages were surveyed from surf zones of 14 ocean‐exposed sandy beaches using purpose‐built surf baited remote underwater video stations.ResultsThe degree of coastal urbanization and connectivity were strongly correlated with the spatial distribution of fish species richness and abundance and were of greater importance to surf fishes than local surf conditions. Urbanization was associated with reductions in the abundance of harvested piscivores and fish species richness. Piscivore abundance and species richness were lowest on highly urbanized coastlines, and adjacent to beaches in wilderness areas where recreational fishing is intense. By contrast, seascape connectivity was correlated with the spatial distribution of omnivore and planktivore abundance. Spatial linkages between surf zones and estuaries were also important to two globally threatened guitarfish that are of international conservation significance.Main conclusionsWe show for the first time how vulnerable and iconic fish species in surf zones are affected by the presence of coastal cities and the attributes of seascapes in which these cities are embedded. It is possible that greater connectivity may lessen ‘urbanization’ impacts for species with broad diets and strong ecological links to other ecosystems – this offers new perspectives in coastal conservation, for fishes and beyond.

Implementation of ARIMA Model to Asses Seasonal Variability Macrobenthic Assemblages

Human activities, including industrial and aquaculture, may have impact on water environment, especially organic enrichment. One of bioindicator of pollution that affect the quality of the water ecosystem is macrobenthic community. In general, the more diverse macrobenthic assemblages indicate the better of the waters quality. Understanding spatial and temporal distribution of macrobenthic abundance has become an important part of research in the field of ecology in understanding the level of environmental disturbance over time. This study discussed the application of the method of Autoregressive Integrated Moving Average (ARIMA) to asses seasonal variability ofmacrobentic assemblages. We found that forecasting using autoregressive integrated moving average method with the model of ARIMA (0,1,1) is obtained the smallest value of the Mean Square Deviation (MSD).

Reproductive phenology of the American Bullfrog in subtropical Brazil: photoperiod as a main determinant of seasonal activity.

The North American bullfrog Lithobates catesbeianus continues to invade ecosystems worldwide, potentially causing population declines and even extinctions. Within its native distribution, bullfrogs show prolonged reproductive seasons and high fertility. However, data on breeding biology of bullfrogs ex-situ in invaded localities mainly comes from anecdotal reports. Understanding how invasive species are adjusting their life histories to new colonized environments is important for conservation purposes. Here we describe temporal and spatial abundance, calling activity, spawning and tadpole distribution of bullfrogs in southern Brazil. Eighteen samplings occurred during one year. The abundance of individuals was positively related to longer photoperiods and higher temperatures. Reproductive activity was also positively associated with longer photoperiods. Calling sites, spawning and tadpoles were associated with microhabitats presenting hydrophytes, which may provide shelter and thermal stability to bullfrogs. The reproductive seasonal activity of bullfrogs can be highly variable across its growing geographical range, but in subtropical Brazil it is associated with photoperiod, a highly predictable abiotic determinant. In our study area, bullfrogs presented a breeding season twice as long as that observed in some native localities. We suggest that management strategies directed to bullfrog populations must consider the habitat structures and seasonal regimes determined by each invaded environment.

Integrating population dynamics models and distance sampling data: a spatial hierarchical state-space approach.

Stochastic versions of Gompertz, Ricker, and various other dynamics models play a fundamental role in quantifying strength of density dependence and studying long-term dynamics of wildlife populations. These models are frequently estimated using time series of abundance estimates that are inevitably subject to observation error and missing data. This issue can be addressed with a state-space modeling framework that jointly estimates the observed data model and the underlying stochastic population dynamics (SPD) model. In cases where abundance data are from multiple locations with a smaller spatial resolution (e.g., from mark-recapture and distance sampling studies), models are conventionally fitted to spatially pooled estimates of yearly abundances. Here, we demonstrate that a spatial version of SPD models can be directly estimated from short time series of spatially referenced distance sampling data in a unified hierarchical state-space modeling framework that also allows for spatial variance (covariance) in population growth. We also show that a full range of likelihood based inference, including estimability diagnostics and model selection,is feasible in this class of models using a data cloning algorithm. We further show through simulation experiments that the hierarchical state-space framework introduced herein efficiently captures the underlying dynamical parameters and spatial abundance distribution. We apply our methodology by analyzing a time series of line-transect distance sampling data for fin whales (Balaenoptera physalus) off the U.S. west coast. Although there were only seven surveys conducted during the study time frame, 1991-2014, our analysis detected presence of strong density regulation and provided reliable estimates of fin whale densities. In summary, we show that the integrative framework developed herein allows ecologists to better infer key population characteristics such as presence of density regulation and spatial variability in a population's intrinsic growth potential.

Comparison of zooplankton data collected by a continuous semi-automatic sampler (CALPS) and a traditional vertical ring net

We compared and evaluated the performance of a Continuous Automatic Litter and Plankton Sampler (CALPS) against the traditional ring net vertical haul. CALPS is a custom-made semi-automatic sampler, which collects water using a pump system at a single depth along a predetermined transect as the ship sails. CALPS underestimated species abundance compared to the ring net by a factor 1.61, but both datasets illustrated a similar species composition, community size structure and good agreement in the spatial distribution of abundance. Our analysis suggests that avoidance of the CALPS is likely to be the main factor responsible for the observed difference in sampling efficiency, but other factors, such as depth, area sampled and zooplankton patchiness, are also likely to play their part. We conclude that whilst the CALPS is not suitable for investigations that require accurate measures of abundance, it is an ideal tool to identify and quantify changes in plankton communities and diversity. A particular advantage over more traditional vertical sampling methods is that it can be integrated within existing multidisciplinary surveys at little extra cost, thus making the CALPS particularly valuable as part of integrated monitoring programmes to underpin policy areas such as the EU Marine Strategy Framework Directive.

The role of submerged trees in the early development of fishes in a Neotropical reservoir.

It was hypothesized that the structural heterogeneity provided by submerged trees positively favours the spatial distribution of fish abundance at early stages of development in an area under the influence of a Neotropical reservoir in the Paraná River basin. The distribution at early stages of development of the most abundant species was evaluated. To remove any possible confounding effect related to local environmental variables, changes in these were also evaluated. Sampling was carried out at sites with and without submerged trees. Among all individuals sampled, 96·1% were classified as larvae and 3·9% as juveniles. The area without submerged trees showed higher total abundance, but there were spatial differences in the distribution of early stage fishes. From the moment the larvae are able to swim actively, they search for sites with a complex structure. The results show that reaches with submerged trees play an important role in the early development of fishes in reservoirs, and, hence, the preservation of those trees is essential to maintain biodiversity in reservoirs.

Variability of whipworm infection and humoral immune response in a wild population of mole voles (Ellobius talpinus Pall.).

Restricted mobility and spatial isolation of social units in gregarious subterranean mammals ensure good defence mechanisms against parasites, which in turn allows for a reduction of immunity components. In contrast, a parasite invasion may cause an increased adaptive immune response. Therefore, it can be expected that spatial and temporal distribution of parasites within a population will correlate with the local variability in the host's immunocompetence. To test this hypothesis, the intra-population variability of a whipworm infestation and the humoral immune response to non-replicated antigens in mole voles (Ellobius talpinus Pall.), social subterranean rodents, was estimated. Whipworm prevalence in mole voles increased from spring to autumn, and this tendency was more pronounced in settlements living in natural meadows compared to settlements in man-made meadows. However, humoral immune response was lowest in animals from natural meadows trapped in autumn. Since whipworm infestation does not directly affect the immunity of mole voles, the reciprocal tendencies in seasonal dynamics and spatial distribution of whipworm abundance and host immunocompetence may be explained by local deterioration of habitat conditions, which increases the probability of an infestation.