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1.
Populations of European wild rabbit (Oryctolagus cuniculus) have been decreasing since the 1950s. Changes in agricultural practices have been suggested as reasons for their decline in Mediterranean landscapes. We evaluated the environmental variables affecting rabbit distribution in a semiarid agricultural landscape of Northeastern Spain. Sampling was performed in 147 sites randomly distributed across Zaragoza province. At each site, data were recorded in five 100 m segments along a 1 km transect, following ecotones between crops and natural-vegetation areas. A rabbit abundance index was estimated from latrine count, pellet density and number of plots with pellets. In addition to environmental variables that have been shown to be related to rabbit abundance in other habitats, as climate, soil hardness and topography of the site, we measured landscape components related to agricultural use, such as structure of natural vegetation in remaining areas non-devoted to agricultural use and distances to different types of crops and to ecotone between crop and natural vegetation. Our results showed that rabbit abundance was positively correlated to yearly mean temperature, February and May mean rainfall, and negatively correlated to September and November mean rainfall, hardness of soil, and site topography. In relation to agricultural use, rabbit abundance was positively correlated to the scrub structure of natural-vegetation areas and negatively correlated to distance to edge between cultivated unirrigated cereal crops (wheat or barley) and yearly resting cereal crops. Rabbit abundance increased only when the edge between alternate cereal crops was less than 50 m from the ecotone between crops and natural vegetation.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
2.
For weak flying insects feeding on two different host plants during their life cycle, such as gall-inducing aphids, patch
and matrix characteristics may play a critical role in patch occupancy and population size in occupied patches. The aims of
the present study were to define the basic patch size of Baizongia pistaciae (L) (Aphididae, Fordini), an aphid inducing galls on Pistacia palaestina Boiss (Anacardiaceae) using a genetic approach, and to estimate the impact of landscape structure and patch quality on patch
occupancy and gall density on occupied trees of this aphid and four other closely related species. Using 42 genetic markers
detected by RAPD-PCR in 117 clones of the galling aphid Baizongia pistaciae, we calculated Wright's F statistics and estimated the number of winged migrants between demes. We found that host trees at least 150 m apart supported
genetically differentiated demes of B. pistaciae, and formed distinct patches. Since the annual cycle of this aphid involves alternation between two different hosts, P. palaestina trees and Poaceae roots, patch – the smallest area that sustains a deme – is a relatively small area that must be composed
of at least a single P. palaestina tree and nearby secondary hosts. To assess the impact of landscape structure and patch quality on patch occupancy and gall
abundance in occupied patches, two field surveys of P. palaestina trees in natural Mediterranean maquis were performed. Among the five species of gall-inducing aphids found, B. pistaciae was the most abundant of those surveyed. Host trees were occupied more often in the ecotone, the transition zone between
Mediterranean closed maquis and open bata, than in the maquis. Mature and old trees were more often occupied than young ones,
and shrubs more often than tree-like plants. There was no difference in the proportion of occupied trees between isolated
host trees or those growing in groups. Species richness showed similar trends. We also found no significant differences in
gall abundance in occupied trees among tree quality categories, except that trees growing in the ecotone tended to carry more
galls than those growing in the maquis. In conclusion, the best patch of gall-inducing aphids seems to be a small area, composed
of an old shrub of P. palaestina standing in an open landscape with nearby secondary hosts, grass roots, available for colonization by winged migrants. 相似文献
3.
Linear habitats are becoming increasingly common as a consequence of habitat fragmentation, and may provide the sole habitat
for some species. Hedgerows are linear features that can vary substantially in structure and quality. Having surveyed 180
hedgerows, in four locations, and sampled their small mammal communities we examined the effect of physical hedgerow attributes
on the abundance of small mammal species. Using three elements of landscape structure, we explored whether variation was best
explained by the Random Sample Hypothesis (that small islands represent a random sample of those species populating larger
areas), or by the Fragmentation Hypothesis (that species abundance will decrease with a loss of habitat area). We tested the
relationship between the relative abundance of small mammals and 1. hedgerow connectivity; 2. total habitat availability and
3. local habitat complexity. We then explored the predictive power of combinations of these habitat variables. Connectivity
was a positive predictor of wood mice Apodemus sylvaticus, and hedgerow gappiness was a negative predictor of bank voles Clethrionomys glareolus. The total amount of habitat available (hedgerow width, height and length) was a positive indicator of total small mammal
biomass. These results support the Fragmentation Hypothesis that species abundance and distribution decrease with a loss of
habitat area. The preservation of linear and associated habitats may therefore be important in maintaining metapopulations
of the species we studied. 相似文献
4.
Jacques Blondel Philippe Perret Marie Maistre Paula Cristina Dias 《Landscape Ecology》1992,6(3):213-219
We investigate whether a mosaic of habitats of different quality functions as a source-sink system for the Blue Tit Parus caeruleus L. Breeding parameters, especially laying date, clutch size and breeding success have been studied in relation to the food supply in three habitats: two habitats, one rich and one poor, next to each other on the mainland (southern France) and one poor habitat on the island of Corsica. Food resources are more abundant and are available earlier in the season in the rich habitat than in both the mainland and the island poor habitats. The timing of breeding is nicely timed on the food peak of abundance in the rich mainland habitat and in the poor insular one but tits are mistimed in the poor mainland habitat because they start to breed too early in relation to food availability. Such patterns strongly suggest that the rich mainland habitat where birds produce many fledglings functions as a source from which birds emigrate in the poor habitat which functions as a sink. These birds which are genetically programmed to breed in the source habitat become mistimed in the sink. Tits on Corsica which are isolated from any mainland population have adjusted their breeding traits on the local patterns of food availability and abundance. This hypothesis is supported by the existence of a strong genetic component of laying date which has been experimentally proved. 相似文献
5.
Widespread adoption of genetically modified glyphosate-resistant (GR) crops in the US has dramatically changed the agricultural
landscape to one that selects for establishment and spread of weedy species resistant to glyphosate, a commonly applied herbicide.
Weed species that possess the means to readily spread across the landscape will be contained by weed management strategies
that limit weed establishment and prevent seed set. An empirically-derived simulation model was developed to explore GR Conyza canadensis spread in relation to characteristics of the agricultural landscape. C. canadensis seeds are carried in the wind and move among fields and therefore, access high quality habitat (GR crops) at long distances.
The baseline scenario was the current GR adoption levels in many US agricultural landscapes with corn and soybean rotated
annually. Alternate scenarios examined the interacting effects of management uniformity (GR crop adoption) and increased landscape
richness (three crops: corn, soybean, alfalfa, instead of two), over a 10 year simulation period. When landscape uniformity
increased (increased GR corn adoption), 3× more fields would be infested with the resistant biotype and a specific field would
have up to 24% greater likelihood of being infested compared to the current GR crop adoption levels. Increased landscape richness
(adding alfalfa as a third crop) slightly decreased GR C. canadensis abundance. Reduced GR management uniformity by way of reducing GR soybeans to half their current adoption levels had the
greatest impact on spread and prevented GR C. canadensis from reaching high abundance. Large-scale reliance on glyphosate for weed management has increased high-fitness habitat and
will result in rapid spread of glyphosate-resistant weeds. Without significant reductions of glyphosate use and without spatial
coordination of weed and crop management practices, GR weeds will continue to spread rapidly and impact agricultural practices
in areas reliant on glyphosate. 相似文献
6.
Assessing the associations between spatial patterns in population abundance and environmental heterogeneity is critical for understanding various population processes and for managing species and communities. This study evaluates responses in the abundance of the European rabbit (Oryctolagus cuniculus), an important prey for predators of conservation concern in Mediterranean ecosystems, to environmental heterogeneity at different spatial scales. Multi-scale habitat models of rabbit abundance in three areas of Doñana, south-western Spain, were developed using a spatially extensive dataset of faecal pellet counts as an abundance index. The best models included habitat variables at the three spatial scales examined: distance from lagoons (broad scale), mean landscape shrub coverage and interspersion of pastures (home-range scale), and shrub and pasture cover (microhabitat scale). These variables may well have been related to the availability of food and refuge for the species at the different scales. However, the models’ fit to data and their predictive accuracy for an independent sample varied among the study regions. Accurate predictions in some areas showed that the combination of variables at various spatial scales can provide a reliable method for assessing the abundance of ecologically complex species such as the European rabbit over large areas. On the other hand, the models failed to identify abundance patterns in a population that suffered the strongest demographic collapse after viral epidemics, underlining the difficulty of generalizing this approach. In the latter case, factors difficult to implement in static models such as disease history and prevalence, predator regulation and others may underlie the lack of association. Habitat models can provide useful guidelines for the management of landscape attributes relevant to rabbits and help improve the conservation of Mediterranean communities. However, other influential factors not obviously related to environmental heterogeneity should also be analyzed in more detail. 相似文献
7.
In an increasingly human-dominated landscape, effective management of disturbance-maintained ecosystems, such as grasslands
and savannas, is critical to the conservation of biodiversity. Yet, the response of individual organisms to landscapes created
by disturbances and management is rarely studied. In this study, we examined the endangered Karner blue butterfly, Lycaeides melissa samuelis, in a heterogeneous oak savanna. Our objective was to quantify the butterfly’s habitat use and behavior to assess the effects of prescribed burning. The oak
savanna management in Ohio, USA divides each Karner blue site (n = 4) into three units. Each one-third unit is then burned, mowed, or unmanaged in an annual rotation within each site, and
the result is a fire return interval of ~3 years. Our surveys measured habitat use, while behavior observations quantified
reproduction and foraging for the two annual broods. Our habitat use results showed burned treatments were recolonized quickly,
but there was not a clear selection for burned treatments. Foraging rates were similar in all treatments; however, females
oviposited significantly less in unmanaged treatments (only 5 of 127 ovipositions). This oviposition preference was likely
due to habitat degradation and the availability of recently burned, early successional habitat. Since Karner blues avoided
reproduction in units unburned for ≥4 years, these units could be burned to create high quality early successional habitat.
These results demonstrate how behavioral decisions can be pivotal forces driving spatial population dynamics. Our case study
demonstrates how a fine-scale landscape perspective combined with measurements of behavioral processes can assist with management
decision-making. 相似文献
8.
This study describes the demographic features of a population of Sigmodon hispidus utilizing the habitat mosaic provided by a Carolina Bay on the Atlantic coastal plain of South Carolina. A total of 71 cotton rats were captured 160 times on a 4 ha grid during a winter decline from 25/ha to less that 1/ha. Body weights of adults declined until early February and then increased; those of subadults grew very slowly until February followed by a spurt in growth. Weight gain did not differ between survivors and non-survivors for males, but female survivors gained 1.5 g per week more than non-survivors. Female subadults exhibited higher mortality early in the decline and males later.Adult females were randomly distributed across 8 microhabitats, whereas adult males were almost exclusively confined to heavy Rubus cover. Subadult males used wet sites more than any other cohort; subadult females were widely distributed using drier sites most frequently. By the end of the decline, all survivors were localized in Rubus-dominated patches. No statistically significant changes in electromorph genotypes or allele frequencies were detected, but survivors had a higher frequency of the F-allele at the adenylate kinase locus than did non-survivors (42.3% vs. 16.7%).Our findings affirm the importance of a landscape perspective in understanding the population dynamics of cotton rats, and show how a habitat mosaic influences survival differentially among sex-age cohorts. 相似文献
9.
The storm that struck France on december 26th and 28th 1999 felled 140 million m3 of timber and had a high economic, social and landscape impact. This event offered the opportunity to study large-scale patterns in populations of forest insect pests that would benefit from the abundant breeding material. A large-scale survey was carried out in France in 2000 to sample the most frequently observed species developing on spruce (Ips typographus, Pityogene schalcographus) and pine (Tomicus piniperda, Ips sexdentatus) in 898 locations distributed throughout wind-damaged areas. The local abundance of each species scored on a 0 to 5 scale was analysed using geostatistical estimators to explore the extent and intensity of spatial autocorrelation, and was related to site, stand, and neighbourhood landscape metrics of the forest cover (in particular the interconnection with broadleaf forest patches) found within dispersal distance. All species but I. sexdentatus, which was much less abundant, displayed large-scale spatial dependence and regional variations in abundance. Lower infestation levels per tree (windfalls and standing trees) were observed in stands with a high proportion of wind-damaged trees, which was interpreted as the result of beetles distributing themselves among the available breeding material. More infestations were observed in wind-broken trees as compared to wind-felled trees. More importantly, populations showed significant relationships with the structure of coniferous stands (in particular with the number of coniferous patches). T. piniperda population levels were negatively correlated to the amount of coniferous edge shared with broadleaf forest patches, possibly because of the disruptive effect of non-host volatiles on host-finding processes at the landscape-scale. The differences observed between species regarding patterns and relationships to site, stand, and forest cover characteristics are discussed in relation to the ecological characteristics of each species. 相似文献
10.
Studies on the distribution of mammalian carnivores in fragmented landscapes have focused mainly on structural aspects such
as patch and landscape features; similarly, habitat connectivity is usually associated with landscape structure. The influence
of food resources on carnivore patch use and the important effect on habitat connectivity have been overlooked. The aim of
this study is to evaluate the relative importance of food resources on patch use patterns and to test if food availability
can overcome structural constraints on patch use. We carried out a patch-use survey of two carnivores: the beech marten (Martes foina) and the badger (Meles meles) in a sample of 39 woodland patches in a fragmented landscape in central Italy. We used the logistic model to investigate
the relative effects on carnivore distribution of patch, patch neighbourhood and landscape scale variables as well as the
relative abundance of food resources. Our results show how carnivore movements in fragmented landscapes are determined not
only by patch/landscape structure but also by the relative abundance of food resources. The important take-home message of
our research is that, within certain structural limits (e.g. within certain limits of patch isolation), by modifying the relative
amount of resources and their distribution, it is possible to increase suitability in smaller/relatively isolated patches.
Conversely, however, there are certain thresholds above which an increase in resources will not achieve high probability of
presence. Our findings have important and generalizable consequences for highly fragmented landscapes in areas where it may
not be possible to increase patch sizes and/or reduce isolation so, for instance, forest regimes that will increase resource
availability could be implemented.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
11.
James C. Beasley Zachary H. Olson Guha Dharmarajan Timothy S. EaganII Olin E. RhodesJr. 《Landscape Ecology》2011,26(7):937-950
Human land-use practices have dramatically altered the composition and configuration of native habitats throughout many ecosystems.
Within heterogeneous landscapes generalist predators often thrive, causing cascading effects on local biological communities,
yet there are few data to suggest how attributes of fragmentation influence local population dynamics of these species. We
monitored 25 raccoon (Procyon lotor) populations from 2004 to 2009 in a fragmented agricultural landscape to evaluate the influence of local and landscape habitat
attributes on spatial and temporal variation in demography. Our results indicate that agricultural ecosystems support increased
densities of raccoons relative to many other rural landscapes, but that spatial and temporal variation in demography exists
that is driven by non-agricultural habitat attributes rather than the availability of crops. At the landscape scale, both
density and population stability were positively associated with the size and contiguity of forest patches, while at the local
scale density was positively correlated with plant diversity and the density of tree cavities. In addition, populations occupying
forest patches with greater levels of plant diversity and stable water resources exhibited less temporal variability than
populations with limited plant species complexity or water availability. The proportion of populations comprised of females
was most strongly influenced by the availability of tree cavities and soft mast. Despite the abundance of mesopredators in
heterogeneous landscapes, our results indicate that all patches do not contribute equally to the regional abundance and persistence
of these species. Thus, a clear understanding of how landscape attributes contribute to variation in demography is critical
to the optimization of management strategies. 相似文献
12.
Throughout most of the north-west Iberian Peninsula, chestnut (Castanea sativa) woods are the principal deciduous woodland, reflecting historical and ongoing exploitation of indigenous forests. These
are traditionally managed woodlands with a patchy distribution. Eurasian nuthatches (Sitta europaea) inhabit mature deciduous woods, show high site fidelity, and are almost exclusively found in chestnut woods in the study
area. We studied the presence and abundance of nuthatch breeding pairs over two consecutive years, in relation to the size,
degree of isolation and intensity of management of 25 chestnut woods in NW Spain. Degree of isolation was assessed in view
of the presence of other woodland within a 1-km band surrounding the study wood. Wood size was the only variable that significantly
predicted the presence of breeding pairs (in at least one year, R
2 = 0.69; in both years, R
2 = 0.50). The number of pairs was strongly predicted by wood size, isolation and management (R
2 = 0.70 in 2004; R
2 = 0.84 in 2005); interestingly, more isolated woods had more breeding pairs. Breeding density was likewise significantly
or near-significantly (P ≤ 0.1) higher in small isolated woods, which is possibly attributable to lower juvenile dispersal in lightly forested areas
and/or to lower predator density in smaller and more isolated patches. Breeding density was higher (though not significantly
so) in more heavily managed woods, possibly due to the presence of larger chestnut crops and larger trees (with higher nuthatch
prey abundance). Our findings highlight the complexity of the relationships between the patch properties and the three studied
levels (presence, number and density of pairs), and also the importance of traditionally managed woodlands for the conservation
of forest birds. 相似文献
13.
The impact of agricultural practices on the dynamics of weed invasion in a rural landscape was studied by describing the spatial distribution of Chaerophyllum aureum populations colonising less intensive managed hay meadows. Polyphenol compounds were used as individual markers to identify the structure of C. aureum diversity, in terms of its scale and patterns, within and between fields along the bottom of a Pyrenean valley. The results revealed, firstly, the existence of a dominant `genotype' successfully colonising the entire area, and secondly, the maintenance of high levels of polyphenol diversity within five different populations. This spatial arrangement of `genetic' population diversity was obviously not related to the natural reproduction and dispersal patterns of this species, but to human practices of hay production, the principal effect of which is to mix seeds of different genetic origin and thus accelerate and amplify the colonisation process of adapted `genotypes'. 相似文献
14.
A two-year field study investigated the possible effects of grain sorghum (Sorghum bicolor [L.] Moench) and uncultivated areas on the abundance of generalist predators in commercially-managed cotton (Gossypium hirsutum L.) fields in Texas, USA. From 63 to 70 fields were sampled for pests and predators over nine consecutive weeks during early stages of cotton development. Additional data on agronomic practices and landscape composition at three spatial scales were also collected for each field. Stepwise regression analyses were used to determine the relationships of landscape, agronomic and prey variables to the abundance of generalist predators. Because the variables most closely linked to predator levels could vary over time, separate regressions were conducted for three time periods corresponding to stages of grain sorghum growth (half-bloom, hard-dough, maturity) in each year. Significant relationships between predator abundance and agricultural landscape composition appear in both years and in all three time periods, but the specific relationships of landscape variables to cotton predator levels differed between and within years. At maturity in 2001, predator levels rose as the amount of uncultivated land from 1.6 to 3.2 km distant and the perimeter shared with grain sorghum increased. During 2002, the area of grain sorghum (half-bloom) and uncultivated land (hard-dough) within 1.6 km of cotton fields were both positively related to predator numbers. Cotton planting dates and the abundance of cotton fleahoppers (Pseudatomoscelis seriatus [Reuter]) were also strongly linked to predator numbers during both years. Results suggest that the total amount of grain sorghum or uncultivated land in an area is more important than the presence of these habitats adjacent to cotton fields, and that landscape composition may sometimes be the most important factor in determining predator abundance. 相似文献
15.
Connecting phenological predictions with population growth rates for mountain pine beetle,an outbreak insect 总被引：1，自引：0，他引：1
It is expected that a significant impact of global warming will be disruption of phenology as environmental cues become disassociated
from their selective impacts. However there are few, if any, models directly connecting phenology with population growth rates.
In this paper we discuss connecting a distributional model describing mountain pine beetle phenology with a model of population
success measured using annual growth rates derived from aerially detected counts of infested trees. This model bridges the
gap between phenology predictions and population viability/growth rates for mountain pine beetle. The model is parameterized
and compared with 8 years of data from a recent outbreak in central Idaho, and is driven using measured tree phloem temperatures
from north and south bole aspects and cumulative forest area impacted. A model driven by observed south-side phloem temperatures
and that includes a correction for forest area previously infested and killed is most predictive and generates realistic parameter
values of mountain pine beetle fecundity and population growth. Given that observed phloem temperatures are not always available,
we explore a variety of methods for using daily maximum and minimum ambient temperatures in model predictions. 相似文献
16.
Current velocity and spatial scale as determinants of the distribution and abundance of two rheophilic herbivorous insects 总被引：4，自引：0，他引：4
Organisms frequently show marked preferences for specific environmental conditions, but these preferences may change with landscape scale. Patterns of distribution or abundance measured at different scales may reveal something about an organism's perception of the environment. To test this hypothesis, we measured densities of two herbivorous aquatic insects that differed in body morphology and mobility in relation to current velocity measured at different scales in the upper Colorado River (Colorado, USA). Streambed densities of the caddisfly larva Agapetus boulderensis (high hydrodynamic profile, low mobility) and mayfly nymph Epeorus sp. (low hydrodynamic profile, high mobility) were assessed at 3 spatial scales: whole riffles, individual cobbles within riffles, and point locations on cobbles. Riffles were several meters in extent, cobbles measured 10–30 cm in size, and the local scale was within a few centimeters of individual larvae (themselves ca. 0.5–1.0 cm in size). We also quantified the abundance of periphytic food for these herbivores at the cobble and riffle scales. Agapetus favored slow current (<30 cm s–1) across all scales. Epeorus, by contrast, favored fast current (60–80 cm s–1) at the local and riffle scale, but not at the cobble scale. Only Agapetus showed a significant relationship to current at the cobble scale, with greatest larval densities occurring at velocities near 30 cm s–1. We had predicted an inverse correlation between grazer density and periphytic abundance; however, this occurred only for Agapetus, and then only at the cobble scale. These data suggest that organisms respond to environmental gradients at different spatial scales and that the processes driving these responses may change with scale, e.g., shifting from individual habitat selection at local and cobble scales to population responses at the riffle scale. This study also highlights the importance of using the appropriate scale of measurement to accurately assess the relationship between organisms and environmental gradients across scale. 相似文献
17.
Influence of within-field and landscape factors on aphid predator populations in wheat 总被引：3，自引：0，他引：3
Elliott Norman C. Kieckhefer Robert W. Lee Jang-Hoon French Bryan W. 《Landscape Ecology》1999,14(3):239-252
The influence of prey density, within-field vegetation, and the composition and patchiness of the surrounding landscape on the abundance of insect predators of cereal aphids was studied in wheat fields in eastern South Dakota, USA. Cereal aphids, aphid predators, and within-field vegetation were sampled in 104 fields over a three year period (1988–1990). The composition and patchiness of the landscape surrounding each field were determined from high altitude aerial photographs. Five landscape variables, aggregated at three spatial scales ranging from 2.6 km2 to 581 km2, were measured from aerial photographs. Regression models incorporating within-field and landscape variables accounted for 27–49% of the variance in aphid predator abundance in wheat fields. Aphid predator species richness and species diversity were also related to within-field and landscape variables. Some predators were strongly influenced by variability in the composition and patchiness of the landscape surrounding a field at a particular spatial scale while others responded to variability at all scales. Overall, predator abundance, species richness, and species diversity increased with increasing vegetational diversity in wheat fields and with increasing amounts of non-cultivated lands and increasing patchiness in the surrounding landscape. 相似文献
18.
19.
Spatial relationship between human population density, land use intensity and biodiversity in the Czech Republic 总被引：1，自引：0，他引：1
We test a hypothesis about the spatial coincidence of human population density and species richness, and analyze effects of land conversion and ecosystem use on species richness and landscape diversity in human dominated Central European country, the Czech Republic. We calculated fraction of aboveground net primary productivity appropriated by humans and compared it to the species richness of vertebrate, invertebrate and plant groups and to landscape diversity index in 560 mapping grid squares with grid size approximately 130?km2. Spatial correlations and regressions were established between human population density, appropriation of net primary production, land cover and biodiversity. We found positive spatial coincidence between human population density and species richness. Although the amount of net primary production was not related to species richness in general, we found significant negative spatial relationship between ecosystem use intensity and landscape diversity. As the area of the Czech Republic exhibits relatively high land use intensities, spatial patterns of human impacts have important implications for land management and biodiversity conservation in a cultural landscape. 相似文献
20.
Tick density and population dynamics are important factors in the ecological processes involved in pathogen circulation in
a habitat. These characteristics of tick populations are closely linked to habitat suitability, which reflects the limiting
ecological factors and landscape features affecting tick populations; however, little work has been done on the regional assessment
of habitat suitability. In this study, a regional model for the distribution and abundance of the tick Ixodes ricinus in central Spain is developed. An occurrence and an abundance model were constructed; climate and vegetation variables were
found to be the main predictors of both occurrence and density in a relatively homogeneous matrix of habitat patches, whereas
topographical variables were found to have small contributions and were therefore discarded. The residuals of the abundance
model showed good correlation with the isolation of each patch. The predictive power of the abundance model was greatly enhanced
by inclusion of the traversability (a measure of the permeability of each patch to the propagules of the metapopulation) and
recruitment (an index of the relative importance of each patch to the traffic through the entire habitat network). The removal
from the landscape of the patches whose recruitment values were in the top 10% has a critical effect on tick density, an effect
not observed when patches are removed at random. These results indicate that permanent tick populations can be sustained only
in landscapes containing a minimum network of viable sites. Graph theory and measurements of patch isolation should prove
to be important elements in the forecasting of tick abundance and the management of the features underlying the landscape
ecology of tick populations and pathogen circulation in the field. 相似文献