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1.
Rehabilitation of Semiarid Landscapes in Australia. II. Restoring Vegetation Patches 总被引:2,自引:0,他引:2
This paper describes a practical technique, tested experimentally, for rehabilitating degraded semiarid landscapes in Australia. This rehabilitation technique is based on the ecological principle that semiarid landscapes are spatially organized as patchy, source-sink systems; this patchy organization functions to conserve limited water and nutrients within the system. The aim was to rebuild vegetation patchiness, lost through decades of utilization of these landscapes as rangelands. Patches were reconstructed from large tree branches and shrubs obtained locally and placed in elongated piles along contours. These piles of branches were very effective in recreating productive soil patches within the landscape, as described in part I of this study. These new patchy habitats promoted the establishment and growth of perennial grasses. Although the foliage cover of these grasses declined into a drought, which started before the end of the experiment, plant survivorship remained high. This suggests that patches also function as refugia for organisms during droughts. The patches of branches remained robust and functional, even under grazing impacts, although plant growth and survival were significantly higher within an ungrazed paddock than in a grazed paddock. 相似文献
2.
Habitat fragmentation and loss affect population stability and demographic processes, increasing the extinction risk of species. We studied Anolis heterodermus populations inhabiting large and small Andean scrubland patches in three fragmented landscapes in the Sabana de Bogotá (Colombia) to determine the effect of habitat fragmentation and loss on population dynamics. We used the capture‐mark‐recapture method and multistate models to estimate vital rates for each population. We estimated growth population rate and the most important processes that affect λ by elasticity analysis of vital rates. We tested the effects of habitat fragmentation and loss on vital rates of lizard populations. All six isolated populations showed a positive or an equilibrium growth rate (λ = 1), and the most important demographic process affecting λ was the growth to first reproduction. Populations from landscapes with less scrubland natural cover showed higher stasis of young adults. Populations in highly fragmented landscapes showed highest juvenile survival and growth population rates. Independent of the landscape's habitat configuration and connectivity, populations from larger scrubland patches showed low adult survivorship, but high transition rates. Populations varied from a slow strategy with low growth and delayed maturation in smaller patches to a fast strategy with high growth and early maturation in large patches. This variation was congruent with the fast‐slow continuum hypothesis and has serious implications for Andean lizard conservation and management strategies. We suggest that more stable lizard populations will be maintained if different management strategies are adopted according to patch area and habitat structure. 相似文献
3.
Aaron L. Hoffman Julian D. Olden Jeremy B. Monroe N. LeRoy Poff Todd Wellnitz John A. Wiens 《Oikos》2006,115(2):358-368
Animal movements are influenced by the structure and arrangement of patches in a landscape. Most movement studies occur in terrestrial landscapes, though aquatic landscapes are equally heterogeneous and feature patches that differ in resistance to animal movements. Furthermore, the variable and highly directional flow of water over streambed landscapes is a unique environmental element, yet its constraint on animal movement is poorly understood. This study examines how habitat availability in a streambed landscape interacts with current velocity to affect movement patterns of two benthic grazers: glossosomatid caddisfly larvae (Agapetus boulderensis) and pulmonate snails (Physa sp.). Using experimental streambed landscapes, we found that Agapetus traveled farther as availability of smooth habitat (composed of low diatom turfs) increased compared to tall, structured filamentous stands, but only did so in slow current velocities. Swifter flows caused restricted movement of Agapetus and more upstream‐oriented paths, but only in smooth landscapes where the potential for flow refugia from filamentous stands was minimal. Similarly, increasing proportions of smooth habitat facilitated greater net displacement of Physa using more upstream‐oriented paths. Higher current velocities caused Physa to move faster, a pattern demonstrated only in smooth landscapes. Our results illustrate a strong interaction between benthic habitat structure and current velocity in shaping patterns of grazer movements in a streambed landscape. Our study also suggests that the flow of water be considered not only a strong environmental gradient in streams, but also an interactive landscape feature that can combine with streambed structure to determine the permeability of patches to the movement of benthic organisms. Landscape ecology has mainly focused on terrestrial environments, and this study offers insight into some of the unique processes that may shape animal movement in aquatic environments. 相似文献
4.
5.
Agent-based model approach to optimal foraging in heterogeneous landscapes: effects of patch clumpiness 总被引:1,自引:0,他引:1
Optimal foraging theory concerns animal behavior in landscapes where food is concentrated in patches. The efficiency of foraging is an effect of both the animal behavior and the geometry of the landscape; furthermore, the landscape is itself affected by the foraging of animals. We investigated the effect of landscape heterogeneity on the efficiency of an optimal forager. The particular aspect of heterogeneity we considered was "clumpiness"– the degree to which food resource patches are clustered together. The starting point for our study was the framework of the Mean Value Theorem (MVT) by Charnov. Since MVT is not spatially explicit, and thus not apt to investigate effects of clumpiness, we built an agent-based (or individual-based) model for animal movement in discrete landscapes extending the MVT. We also constructed a model for generating landscapes where the clumpiness of patches can be easily controlled, or "tuned", by an input parameter. We evaluated the agent based model by comparing the results with what the MTV would give, i.e. if the spatial effects were removed. The MVT matched the simulations best on landscapes with random patch configuration and high food recovery rates. As for our main question about the effects of clumpiness, we found that, when landscapes were highly productive (rapid food replenishment), foraging efficiency was greatest in clumped landscapes. In less productive landscapes, however, foraging efficiency was lowest in landscapes with a clumped patch distribution. 相似文献
6.
A Scaling Rule for Landscape Patches and How It Applies to Conserving Soil Resources in Savannas 总被引:12,自引:4,他引:8
Scaling issues are complex, yet understanding issues such as scale dependencies in ecological patterns and processes is
usually critical if we are to make sense of ecological data and if we want to predict how land management options, for example,
are constrained by scale. In this article, we develop the beginnings of a way to approach the complexity of scaling issues.
Our approach is rooted in scaling functions, which integrate the scale dependency of patterns and processes in landscapes
with the ways that organisms scale their responses to these patterns and processes. We propose that such functions may have
sufficient generality that we can develop scaling rules—statements that link scale with consequences for certain phenomena
in certain systems. As an example, we propose that in savanna ecosystems, there is a consistent relationship between the size
of vegetation patches in the landscape and the degree to which critical resources, such as soil nutrients or water, become
concentrated in these patches. In this case, the features of the scaling functions that underlie this rule have to do with
physical processes, such as surface water flow and material redistribution, and the ways that patches of plants physically
“capture” such runoff and convert it into plant biomass, thereby concentrating resources and increasing patch size. To be
operationally useful, such scaling rules must be expressed in ways that can generate predictions. We developed a scaling equation
that can be used to evaluate the potential impacts of different disturbances on vegetation patches and on how soils and their
nutrients are conserved within Australian savanna landscapes. We illustrate that for a 10-km2 paddock, given an equivalent area of impact, the thinning of large tree islands potentially can cause a far greater loss
of soil nitrogen (21 metric tons) than grazing out small grass clumps (2 metric tons). Although our example is hypothetical,
we believe that addressing scaling problems by first conceptualizing scaling functions, then proposing scaling rules, and
then deriving scaling equations is a useful approach. Scaling equations can be used in simulation models, or (as we have done)
in simple hypothetical scenarios, to collapse the complexity of scaling issues into a manageable framework.
Received 8 December 1998; accepted 17 August 1999. 相似文献
7.
Pavlacky DC Possingham HP Lowe AJ Prentis PJ Green DJ Goldizen AW 《The Journal of animal ecology》2012,81(5):940-952
1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations. 2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration. 3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes. 4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners. 5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes. 相似文献
8.
The arrangement of resources in patchy landscapes: effects on distribution, survival, and resource acquisition of chironomids 总被引:3,自引:0,他引:3
The spatial arrangement of resources in patchy habitats influences the distribution of individuals and their ability to acquire
resources. We used Chironomus riparius, a ubiquitous aquatic insect that uses leaf particles as an important resource, to ask how the dispersion of resource patches
influences the distribution and resource acquisition of mobile individuals in patchy landscapes. Two experiments were conducted
in replicated laboratory landscapes (38×38 cm) created by arranging sand and leaf patches in a 5×5 grid so that the leaf patches
were either aggregated or uniformly dispersed in the grid. One-day-old C. riparius larvae were introduced into the landscapes in one of three densities (low, medium, high). In experiment 1, we sampled larvae
and pupae by coring each patch in each landscape 3, 6, 12, or 24 days after adding larvae. In experiment 2, emerging adults
were collected daily for 42 days from each patch in each landscape. In aggregated landscapes, individuals were aggregated
in one patch type or the other during a particular developmental stage, but the ”preferred” type changed depending on developmental
stage and initial density. Adult emergence was lower by about 30% in all aggregated landscapes. In dispersed landscapes, individuals
used both types of patch throughout their life cycles at all initial densities. Thus, patch arrangement influences the distribution
of mobile individuals in landscapes, and it influences resource acquisition even when average resource abundance is identical
among landscapes. Regardless of patch arrangement, high initial density caused accumulation of early instars in edge patches,
75% mortality of early instars, a 25% increase in development time, and a 60% reduction in adult emergence. Because mortality
was extremely high among early-instar larvae in high-density treatments, we do not have direct evidence that the mechanism
by which patch arrangement operates is density dependent. However, the results of our experiments strongly suggest that dispersion
of resource patches across a landscape reduces local densities by making non-resource patches available for use, thereby reducing
intraspecific competition.
Received: 20 July 1999 / Accepted: 28 January 2000 相似文献
9.
Habitat loss and fragmentation are the leading causes of species’ declines and extinctions. A key component of studying population response to habitat alteration is to understand how fragmentation affects population connectivity in disturbed landscapes. We used landscape genetic analyses to determine how habitat fragmentation due to timber harvest affects genetic population connectivity of the coastal tailed frog (Ascaphus truei), a forest-dwelling, stream-breeding amphibian. We compared rates of gene flow across old-growth (Olympic National Park) and logged landscapes (Olympic National Forest) and used spatial autoregression to estimate the effect of landscape variables on genetic structure. We detected higher overall genetic connectivity across the managed forest, although this was likely a historical signature of continuous forest before timber harvest began. Gene flow also occurred terrestrially, as connectivity was high across unconnected river basins. Autoregressive models demonstrated that closed forest and low solar radiation were correlated with increased gene flow. In addition, there was evidence for a temporal lag in the correlation of decreased gene flow with harvest, suggesting that the full genetic impact may not appear for several generations. Furthermore, we detected genetic evidence of population bottlenecks across the Olympic National Forest, including at sites that were within old-growth forest but surrounded by harvested patches. Collectively, this research suggests that absence of forest (whether due to natural or anthropogenic changes) is a key restrictor of genetic connectivity and that intact forested patches in the surrounding environment are necessary for continued gene flow and population connectivity. 相似文献
10.
Alesandro S. Santos Eliana Cazetta Pavel Dodonov Deborah Faria Fernanda A. Gaiotto 《Ecology and evolution》2016,6(18):6586-6598
Habitat loss represents one of the main threats to tropical forests, which have reached extremely high rates of species extinction. Forest loss negatively impacts biodiversity, affecting ecological (e.g., seed dispersal) and genetic (e.g., genetic diversity and structure) processes. Therefore, understanding how deforestation influences genetic resources is strategic for conservation. Our aim was to empirically evaluate the effects of landscape‐scale forest reduction on the spatial genetic structure and gene flow of Euterpe edulis Mart (Arecaceae), a palm tree considered a keystone resource for many vertebrate species. This study was carried out in nine forest remnants in the Atlantic Forest, northeastern Brazil, located in landscapes within a gradient of forest cover (19–83%). We collected leaves of 246 adults and 271 seedlings and performed genotyping using microsatellite markers. Our results showed that the palm populations had low spatial genetic structure, indicating that forest reduction did not influence this genetic parameter for neither seedlings nor adults. However, forest loss decreased the gene flow distance, which may negatively affect the genetic diversity of future generations by increasing the risk of local extinction of this keystone palm. For efficient strategies of genetic variability conservation and maintenance of gene flow in E. edulis, we recommend the maintenance of landscapes with intermediary to high levels of forest cover, that is, forest cover above 40%. 相似文献
11.
Misiones rainforest is one of the most threatened subtropical forests worldwide. Anthropogenic pressure by agriculture and forestry expansion continues transforming landscapes with negative consequences on ecosystem service provision, such as soil erosion control. Understanding how land use and land cover change (LUCC) management, policies, and social factors influenced in the past, allows decision-makers to anticipate potential effects on future land use and soil loss, contributing to the sustainable planning and management of productive activities. We developed three spatially explicit scenarios for Misiones province by 2030 using the Dinamica EGO modeling platform: 1) Business as Usual (BAU), 2) Low Deforestation (ALTlow), and 3) High Deforestation (ALThigh), based on different international and domestic socioeconomic contexts. We used land cover data from 2002 to 2015 as well as biophysical, social-infrastructure, political-administrative factors, and legal restrictions to estimate changes that may occur by 2030. We analyzed magnitude, intensity, and spatial pattern of future forest cover changes through transition rates and a cellular automata allocation model. Moreover, we used the Universal Soil Loss Equation (USLE) integrated into a Geographic Information System (GIS) to determine soil water erosion and soil loss tolerance in each scenario. Our results revealed that around 19% of the remaining native forest would be transformed into either agriculture or cultivated forest by 2030 for all scenarios. In addition, and contrary to that trend, the ALTlow scenario showed a recovery of 3% of native forest. Regarding soil erosion, our study indicated that the mean annual soil loss by 2030 would range from 12.03 to 19.15 t. ha−1.year−1 for ALTlow and ALThigh scenarios, respectively. Additionally, between 21% and 31% of Misiones province showed soil loss values higher than tolerance. Our work shows that a 10% decrease in the deforestation rate, compared to the current rate, would lead not only to a recovery of native forest cover, but also to a reduction in soil loss of about 4.5 Mt.yr−1 by 2030. This study demonstrates the suitability of the applied model to simulate future LUCC processes and provides inputs for decision-making involving natural resource management and the potential impacts of these decisions on ecosystem services. Finally, our results highlight the need for appropriate policies and regulations, especially, in terms of land use change restrictions in areas of high erosion risk. 相似文献
12.
Processes that promote weed invasion are often well-demonstrated, but mechanisms that facilitate ecological resistance to
weed invasion in non-invaded communities, or promote weed persistence in invaded communities, are poorly understood. Yet it
is these processes that must be addressed to achieve sustainable ecological restoration. We surveyed soil heterogeneity in
25 long-ungrazed, unfertilized York gum (Eucalyptus loxophleba Benth. subsp. loxophleba)—jam (Acacia acuminata Benth.) woodlands of the Western Australian wheatbelt to investigate differences in soil characteristics between patches
locally-invaded or non-invaded by widespread exotic annuals. Based on studies in other ecosystems, we hypothesized that (1)
weed persistence is associated with elevated soil resource levels, and (2) of these soil resources, phosphorus is the key
contributor to weed persistence in Western Australian woodlands, that typically occur on phosphorus-impoverished soils. Our
first hypothesis was partly supported, with soil nutrients associated with up to 40% of the variation in cover of exotic annuals.
In particular, low concentrations of total nitrogen, nitrate and available phosphorus are likely to contribute to resistance
to invasion in many non-invaded woodland patches, especially in gaps between trees. However, other non-invaded patches had
comparable nutrient concentrations to invaded patches, suggesting this resistance may be weak at more productive sites or
that patches have not reached a stable equilibrium. Inconsistent with our second hypothesis, exotic annuals were as strongly
correlated with elevated total nitrogen and associated variables as they were with available phosphorus, probably reflecting
a history of grazing without fertilization. We conclude that effectiveness of ‘bottom-up’ approaches to weed control is likely
to differ among ecosystems according to interactions with disturbance history and attributes of the non-invaded community,
even where the weed species or functional types are the same. 相似文献
13.
ávila-Pires’ saddle-back tamarins (Saguinus fuscicollis avilapiresi) and red-cap moustached tamarins (S. mystax pileatus), coexisting in highly stable mixed-species groups, overlapped considerably in their use of plant food resources at an Amazonian
terra firme forest site. Overlap between food types consumed by the two species was particularly high during periods of lowest
fruit availability, when they resorted to a common food supply, primarily the pod exudates of two emergent species of legume
trees (Parkia nitida andParkia pendula) and nectar ofSymphonia globulifera. Within-group interspecific competition did not covary with independent measures of resource availability, contrary to predictions
based on resource partitioning models. A greater number of both saddle-back and moustached tamarins were able to feed for
longer patch residence periods within larger and more productive food patches, whereas small and clumped patches could be
monopolized by the socially and numerically dominant moustached tamarins to the physical exclusion of the smaller-bodied saddle-back
tamarins. Overall rates of interspecific aggression were extremely low, however, partly because patches that could be monopolized
contributed with a minor proportion of either species’ diet. Saddle-backs foraged at lower levels in the understory and encountered
smaller food patches more often, whereas moustached tamarins foraged higher and encountered more larger patches in the middle
canopy. Although the two species led one another to differently-sized patches, moustached tamarins initiated most feeding
bouts and encountered significantly larger and more productive patches that tended to accommodate the entire mixed-species
group. Disadvantages of exploitative and interference feeding competition over plant resources, and advantages of shared knowledge
of food patches, are but one component of the overall cost-benefit relationship of interspecific associations in tamarins. 相似文献
14.
Sean M. Schaeffer Elizabeth Sharp Joshua P. Schimel Jeffery M. Welker 《Global Change Biology》2013,19(11):3529-3539
Rapid temperature and precipitation changes in High Arctic tundra ecosystems are altering the biogeochemical cycles of carbon (C) and nitrogen (N), but in ways that are difficult to predict. The challenge grows from the uncertainty of N cycle responses and the extent to which shifts in soil N are coupled with the C cycle and productivity of tundra systems. We used a long‐term (since 2003) experiment of summer warming and supplemental summer water additions to a High Arctic ecosystem in NW Greenland, and applied a combination of discrete sampling and in situ soil core incubations to measure C and N pools and seasonal microbial processes that might control plant‐available N. We hypothesized that elevated temperature and increased precipitation would stimulate microbial activity and net inorganic N mineralization, thereby increasing plant N‐availability through the growing season. While we did find increased N mineralization rates under both global change scenarios, water addition also significantly increased net nitrification rates, loss of NO3?‐N via leaching, and lowered rates of labile organic N production. We also expected the chronic warming and watering would lead to long‐term changes in soil N‐cycling that would be reflected in soil δ15N values. We found that soil δ15N decreased under the different climate change scenarios. Our results suggest that temperature accelerates biological processes and existing C and N transformations, but moisture increases soil hydraulic connectivity and so alters the pathways, and changes the fate of the products of C and N transformations. In addition, our findings indicate that warmer, wetter High Arctic tundra will be cycling N and C in ways that may transform these landscapes in part leading to greater C sequestration, but simultaneously, N losses from the upper soil profile that may be transported to depth dissolved in water and or transported off site in lateral flow. 相似文献
15.
Andreu Castillo‐Escriv Germn M. Lpez‐Iborra Jordi Cortina Jaume Tormo 《Restoration Ecology》2019,27(1):102-108
Desertification is a major environmental problem in arid and semiarid regions. Tree plantation has been commonly employed to foster the recovery of degraded areas. However, this technique is costly, and their outcomes are often uncertain. Therefore, we evaluated an alternative method for the restoration of degraded semiarid steppes that involved the construction of branch piles to attract frugivores as potential seed‐dispersing birds, promoting seed rain, and fostering the formation of woody patches. We measured the success of branch piles in terms of the number of bird visits and seed input compared to naturally occurring shrub patches. Generally, frugivorous birds visited branch piles less frequently than shrub patches. Yet, branch piles accumulated seeds of patch‐forming shrub species. Seed rain was higher under patches of the dominant shrub Rhamnus lycioides than under branch piles. In contrast, woody patches and branch piles did not differ in seed input of the less abundant Pistacia lentiscus shrub. Our study demonstrates that branch piles are used by frugivorous birds and accumulate seeds of patch‐forming shrubs. Branch piles may be a suitable method to promote the expansion of bird‐dispersed plant species and restore semiarid wooded steppes. However, their efficiency largely depends on pile persistence and economic cost. 相似文献
16.
Spatial heterogeneity and scale‐dependent habitat selection for two sympatric raptors in mixed‐grass prairie
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Sympatric predators are predicted to partition resources, especially under conditions of food limitation. Spatial heterogeneity that influences prey availability might play an important role in the scales at which potential competitors select habitat. We assessed potential mechanisms for coexistence by examining the role of heterogeneity in resource partitioning between sympatric raptors overwintering in the southern Great Plains. We conducted surveys for wintering Red‐tailed hawk (Buteo jamaicensis) and Northern Harrier (Circus cyanea) at two state wildlife management areas in Oklahoma, USA. We used information from repeated distance sampling to project use locations in a GIS. We applied resource selection functions to model habitat selection at three scales and analyzed for niche partitioning using the outlying mean index. Habitat selection of the two predators was mediated by spatial heterogeneity. The two predators demonstrated significant fine‐scale discrimination in habitat selection in homogeneous landscapes, but were more sympatric in heterogeneous landscapes. Red‐tailed hawk used a variety of cover types in heterogeneous landscapes but specialized on riparian forest in homogeneous landscapes. Northern Harrier specialized on upland grasslands in homogeneous landscapes but selected more cover types in heterogeneous landscapes. Our study supports the growing body of evidence that landscapes can affect animal behaviors. In the system we studied, larger patches of primary land cover types were associated with greater allopatry in habitat selection between two potentially competing predators. Heterogeneity within the scale of raptor home ranges was associated with greater sympatry in use and less specialization in land cover types selected. 相似文献
17.
The movement ability of species in fragmented landscapes must be considered if habitat restoration strategies are to allow maximum benefit in terms of increased or healthier wildlife populations. We studied movements of a range of bird species between woodland patches within a high‐altitude Polylepis/matrix landscape in the Cordillera Vilcanota, Peru. Movement rates between Polylepis patches differed across guilds, with arboreal omnivores, arboreal sally‐strikers and nectarivores displaying the highest movement rates, and understorey guilds and arboreal sally‐gleaners the lowest movement rates. Birds tend to avoid flights to more distant neighboring patches, especially when moving from patches which were themselves isolated. The decline in bird flight frequencies with increasing patch isolation followed broken‐stick models most closely, and while we suggest that there is evidence for a decline in between‐patch movements over distances of 30–210 m, there was great variability in movement rates across individual patches. This variability is presumably a result of complex interactions between patch size, quality and configuration, and flight movement patterns of individual bird species. Our study does, however, highlight the contribution small woodland patches make toward fragmented Polylepis ecosystem functioning, and we suggest that, where financial resources permit, small patch restoration would be an important compliment to the restoration of larger woodland patches. Most important is that replanting takes place within 200 m or so of existing larger patches. This will be especially beneficial in allowing more frequent use of woodland elements within the landscape and in improving the total area of woodland patches that are functionally connected. 相似文献
18.
Models of metapopulations have often ignored local community dynamics and spatial heterogeneity among patches. However, persistence of a community as a whole depends both on the local interactions and the rates of dispersal between patches. We study a mathematical model of a metacommunity with two consumers exploiting a resource in a habitat of two different patches. They are the exploitative competitors or the competing predators indirectly competing through depletion of the shared resource. We show that they can potentially coexist, even if one species is sufficiently inferior to be driven extinct in both patches in isolation, when these patches are connected through diffusive dispersal. Thus, dispersal can mediate coexistence of competitors, even if both patches are local sinks for one species because of the interactions with the other species. The spatial asynchrony and the competition-colonization trade-off are usual mechanisms to facilitate regional coexistence. However, in our case, two consumers can coexist either in synchronous oscillation between patches or in equilibrium. The higher dispersal rate of the superior prompts rather than suppresses the inferior. Since differences in the carrying capacity between two patches generate flows from the more productive patch to the less productive, loss of the superior by emigration relaxes competition in the former, and depletion of the resource by subsidized consumers decouples the local community in the latter. 相似文献
19.
Characterizing the post‐recolonization of Antechinus flavipes and its genetic implications in a production forest landscape
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Jose L. Mijangos Carlo Pacioni Peter B. S. Spencer Mia Hillyer Michael D. Craig 《Restoration Ecology》2017,25(5):738-748
Production landscapes, where activities such as timber harvesting, grazing, and resource extraction take place, have considerably reduced the extent of natural habitats. The ecological restoration of these landscapes is, in many cases, the best remaining option to protect biodiversity. However, it is unclear whether restoration designed to avert biodiversity loss in restored landscapes can also maintain genetic diversity in recolonizing faunal populations. We employed core concepts in the field of population genetics to address questions of genetic diversity and gene flow in recolonizing faunal populations, using a small and vagile marsupial (Antechinus flavipes) inhabiting a mined landscape under restoration. We did not detect a disruption of gene flow that led to genetic substructuring, suggesting adequate levels of gene flow across the landscape. Parameters of neutral genetic diversity were high in groups of individuals sampled in both restored and unmined sites. Our results are encouraging as they indicate that ecological restoration has the potential to not just increase available habitat, but also to maintain genetic diversity. However, there is evidence that past anthropogenic disturbances affected the genetics of the population at the regional level. Although restoration at the local level may seem to be successful, it is necessary to manage populations at larger spatial scales than where restoration is conducted, and over long temporal scales, if genetic diversity is to be maintained in restored landscapes. The field of population genetics is an underused tool in ecological restoration yet can provide important insights into how well restoration achieves its goals. 相似文献
20.
Species interactions at the level of fine roots in the field: influence of soil nutrient heterogeneity and plant size 总被引:6,自引:0,他引:6
Interference at the level of fine roots in the field was studied by detailed examination of fine root distribution in small soil patches. To capture roots as they occur in natural three-dimensional soil space, we used a freezing and slicing technique for microscale root mapping. The location of individual roots intersecting a sliced soil core surface was digitized and the identity of shrub and grass roots was established by a chemical technique. Soil patches were created midway between the shrub, Artemisia tridentata, and one of two tussock grasses, Pseudoroegneria spicata or Agropyron desertorum. Some soil patches were enriched with nutrients and others given only deionized water (control); in addition, patches were located between plants of different size combination (large shrubs with small tussock grasses and small shrubs with large tussock grasses). The abundance of shrub and grass roots sharing soil patches and the inter-root distances of individual fine roots were measured. Total average rooting density in patches varied among these different treatment combinations by only a factor of 2, but the proportion of shrub and grass roots in the patches varied sixfold. For the shrub, the species of grass roots sharing the patches had a pronounced influence on shrub root density; shrub roots were more abundant if the patch was shared with Pseudoroegneria roots than if shared with Agropyron roots. The relative size of plants whose roots shared the soil patches also influenced the proportion of shrub and grass roots; larger plants were able to place more roots in the patches than were the smaller plants. In the nutrient-enriched patches, these influences of grass species and size combination were amplified. At the millimeter- to centimeter-scale within patches, shrub and grass roots tended to segregate, i.e., avoid each other, based on nearest-neighbor distances. At this scale, there was no indication that the species-specific interactions were the result of resource competition, since there were no obvious patterns between the proportion of shrub and grass roots of the two species combinations with microsite nutrient concentrations. Other potential mechanisms are discussed. Interference at the fine-root level, and its species-specific character, is likely an influential component of competitive success, but one that is not easily assessed. 相似文献