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1.
Franz Rebele 《应用植被学》2001,4(1):147-156
Abstract. This paper reports on vegetation dynamics on terrestrial, temperate grassland sites at the upper range of the productivity scale, i.e. on abandoned sewage fields (fields once used for waste water disposal) at Berlin‐Blankenfelde, Germany. I studied regeneration and the influence of different management practices (removal of top soil and mowing in late summer). Changes in species composition and cover were followed on permanent plots of 2m × 2m size through five years of vegetation development. At the outset of the experiment the abandoned fields were dominated by dense Urtica dioica /Elymus repens stands. Species richness was 7 species/ 4m2, and it remained low on unmanaged plots during the time of observation (7.6 species/plot in year 5). Removal of 20 cm of top soil caused a severe decline of Urtica and a large increase in species richness (21 species in year 1 after disturbance). Mowing was slightly higher compared with unmown plots on both initially excavated and unexcavated plots. Total cover was always near 100 % (except immediately after top soil removal). Colonization of bare soil was very rapid and in late summer of the first year after disturbance cover already increased towards 100%. On all plots the vegetation was mostly dominated by perennial herbs and grasses. Winter season gaps are occupied by Galium aparine, a large‐seeded annual scrambling climber. Monocarpic perennials behaved as winter annuals in most cases. Woody species were inhibited by dense above‐ground biomass and litter cover. The paper questions whether succession on abandoned sewage fields may proceed towards a woodland stage and advises how vegetation of such hyper‐eutrophicated sites can be managed towards higher diversity. 相似文献
2.
Alexis A. Suazo Jessica E. Spencer E. Cayenne Engel Scott R. Abella 《Biological invasions》2012,14(1):215-227
Habitat modification (i.e., disturbance) and resource availability have been identified as possible mechanisms that may influence
the invasibility of plant communities. In the Mojave Desert, habitat disturbance has increased dramatically over the last
50 years due to increased human activities. Additionally, water availability is considered to be a main limiting resource
for plant production. To elucidate the effects of soil disturbance and water availability on plant invasions, we created experimental
patches where we varied the levels of soil disturbance and water availability in a fully crossed factorial experiment at five
replicated field sites, and documented responses of native and non-native winter annuals. The treatments did not significantly
affect the density (seedlings m−2) of the non-native forb, Brassica tournefortii. However, the relationship between silique production and plant height differed among treatments, with greater silique production
in disturbed plots. In contrast to Brassica, density of the non-native Schismus spp. increased in soil disturbed and watered plots, and was greatest in disturbed plots during 2009 (the second year of the
study). Species composition of the native annual community was not affected by treatments in 2008 but was influenced by treatments
in 2009. The native forb Eriophyllum sp. was most dense on water-addition plots, while density of Chaenactis freemontii was highest in disturbed plots. Results illustrate that habitat invasibility in arid systems can be influenced by dynamics
in disturbance regimes and water availability, and suggest that invasiveness can differ between non-native annual species
and among native annuals in habitats undergoing changing disturbance and precipitation regimes. Understanding the mechanistic
relationships between water availability and non-native plant responses will be important for understanding the effects of
shifting precipitation and vegetation patterns under predicted climate change in arid ecosystems. 相似文献
3.
Niche-based and neutral models of community structure posit distinct mechanisms underlying patterns in community structure;
correlation between species’ distributions and habitat factors points to niche assembly while spatial pattern independent
of habitat suggests neutral assembly via dispersal limitation. The challenge is to disentangle the relative contributions
when both processes are operating, and to determine the scales at which each is important. We sampled shoreline plant communities
on an island in Lake Michigan, varying the extent and the grain of sampling, and used both distance-based correlation methods
and variance partitioning to quantify the proportion of the variation in plant species composition that was attributable to
habitat factors and to spatial configuration independent of habitat. Our results were highly scale dependent. We found no
distance decay of plant community similarity at the island scale (1−33 km). All of the explained variation (32%) in species
composition among samples at this scale was attributed to habitat factors. However, at a site intensively sampled at a smaller
scale (5−1,200 m), similarity of species composition did decay with distance. Using a coarse sampling grain (transects), habitat
factors explained 40% of the variation, but the purely spatial component explained a comparable 22%. Analyzing plots within
transects revealed variation in species composition that was still jointly determined by habitat and spatial factors (18 and
11% of the variance, respectively). For both grain sizes, most of the habitat component was spatially structured, reflecting
an abrupt alongshore transition from sandy dunes to cobble beach. Space per se explained more variation in species composition
at a second site where the habitat transition was more gradual; here, habitat acted as a less selective filter, allowing the
signal of dispersal limitation to be detected more readily. We conclude that both adaptation to specific habitat factors and
habitat-independent spatial position indicative of dispersal limitation determine plant species composition in this system.
Our results support the prediction that dispersal limitation—a potentially, but not necessarily, neutral driver—is relatively
more important at smaller scales. 相似文献
4.
Despite numerous studies on breeding dispersal, it is still unclear how habitat heterogeneity and previous nesting success
interact to determine nest-site fidelity at various spatial scales. In this context, we investigated factors affecting breeding
dispersal in greater snow geese (Anser caerulescens atlanticus), an Arctic breeding species nesting in two contrasting habitats (wetlands and mesic tundra) with variable pattern of snowmelt
at the time of settlement in spring. From 1994 to 2005, we monitored the nesting success and breeding dispersal of individually
marked females. We found that snow geese showed a moderate amount of nest-site fidelity and considerable individual variability
in dispersal distance over consecutive nesting attempts. This variability can be partly accounted for by the annual timing
of snowmelt. Despite this environmental constraint, habitat differences at the colony level consistently affected nesting
success and settlement patterns. Females nesting in wetlands had higher nesting success than those nesting in mesic tundra.
Moreover, geese responded adaptively to spatial heterogeneity by showing fidelity to their nesting habitat, independently
of snowmelt pattern. From year to year, geese were more likely to move from mesic to high-quality wetland habitat, regardless
of previous nesting success and without cost on their subsequent nesting performance. The unpredictability of snowmelt and
the low cost of changing site apparently favour breeding-site dispersal although habitat quality promotes fidelity at the
scale of habitat patches. 相似文献
5.
Annuals represent a significant component of the vegetation of coastal salt marshes and sand dunes. From many points of view, the two habitats might appear to have little in common. Yet both are characterized by episodes of low water potential, marked spatial and temporal heterogeneity and a zonation which, within certain limits, reflects successional change.There are also similarities of distribution. Annuals are dominant usually in the pioneer stages; the Salicornia-dominated low marsh areas are perhaps analogues with strandline ephemeral populations (e.g. Cakile maritima) on the fore-dunes. In mature stages, annuals are associated with small gaps in the matrix of perennials, at least some of these arising from drought or disturbance. Nevertheless populations can reach very high densities.The most striking contrast is phenological; only summer annuals are found on marshes, whereas winter annuals predominate on dunes (except for the strandline). Similarly there is a difference in species richness. Rather few species of annual are typical of marshes while a great many are found on dunes.Properties of the seed bank, survival, reproduction and population regulation are compared in marsh and dune annuals, with special reference to Cakile, Salicornia, Rhinanthus and Vulpia. Interpretations are suggested which take account of environmental predictability and heterogeneity. Finally, the general applicability of simple mathematical models of these populations in the different coastal habitats is considered.Nomenclature follows Clapham, Tutin & Warburg (1981) except where otherwise stated. 相似文献
6.
Black rhino numbers have decreased greatly since the early 1970s, primarily as a result of poaching. A recent strategy to protect rhinos in Kenya has been to establish fenced sanctuaries. This has increased the rhino population and that of other species, but problems have emerged because of limited dispersal and rising animal densities. Unfortunately, how rhino utilize habitat, especially areas called bedding sites, is not well understood. These areas provide shade and may be a critical component of rhino habitat. We measured habitat variables at bedding sites located in bedding plots and compared them with control plots at Sweetwaters Reserve, Kenya. Euclea divinorum was the most common tree in the bedding site comprising 64.3% of the vegetation. Elephant dung was significantly more likely to be found in bedding plots than in control plots which suggests that elephants and rhinos use overlapping habitats. Elephants may be causing damage to the tree species that are important for bedding sites. Resource competition between large herbivores in small reserves is likely to negatively affect the tree species. Black rhino habitat, particularly bedding sites, may be at risk and rhino numbers may decrease. 相似文献
7.
Evidence for community assembly constraints during succession in dune slack plant communities 总被引:1,自引:0,他引:1
Community assembly during succession can be constrained by both local and regional factors. Despite an increasing regional species pool size during succession, we found a limit on the number of species in 1 × 1 m plots in dune slacks. Three alternative hypotheses (habitat heterogeneity, dispersal limitation and niche limitation) explaining this community saturation were tested. A null model analysis showed that species richness in the plots had an unusually low variance suggesting that beta habitat diversity was not likely to explain the limitation on species richness. Because we did not find a correlation between the distribution of species over the slack and their dispersal capacity, we also excluded the dispersal limitation hypothesis. Finally, a guild proportionality analysis revealed that the abundances of forb, graminoid and ruderal species showed low an unusually low variance over all age classes involved. This provides evidence for nonrandom community assembly during succession, likely to be determined by competitive exclusion among species of the same guild. 相似文献
8.
Landscape characteristics influencing the genetic structure of greater sage‐grouse within the stronghold of their range: a holistic modeling approach
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Jeffrey R. Row Sara J. Oyler‐McCance Jennifer A. Fike Michael S. O'Donnell Kevin E. Doherty Cameron L. Aldridge Zachary H. Bowen Bradley C. Fedy 《Ecology and evolution》2015,5(10):1955-1969
Given the significance of animal dispersal to population dynamics and geographic variability, understanding how dispersal is impacted by landscape patterns has major ecological and conservation importance. Speaking to the importance of dispersal, the use of linear mixed models to compare genetic differentiation with pairwise resistance derived from landscape resistance surfaces has presented new opportunities to disentangle the menagerie of factors behind effective dispersal across a given landscape. Here, we combine these approaches with novel resistance surface parameterization to determine how the distribution of high‐ and low‐quality seasonal habitat and individual landscape components shape patterns of gene flow for the greater sage‐grouse (Centrocercus urophasianus) across Wyoming. We found that pairwise resistance derived from the distribution of low‐quality nesting and winter, but not summer, seasonal habitat had the strongest correlation with genetic differentiation. Although the patterns were not as strong as with habitat distribution, multivariate models with sagebrush cover and landscape ruggedness or forest cover and ruggedness similarly had a much stronger fit with genetic differentiation than an undifferentiated landscape. In most cases, landscape resistance surfaces transformed with 17.33‐km‐diameter moving windows were preferred, suggesting small‐scale differences in habitat were unimportant at this large spatial extent. Despite the emergence of these overall patterns, there were differences in the selection of top models depending on the model selection criteria, suggesting research into the most appropriate criteria for landscape genetics is required. Overall, our results highlight the importance of differences in seasonal habitat preferences to patterns of gene flow and suggest the combination of habitat suitability modeling and linear mixed models with our resistance parameterization is a powerful approach to discerning the effects of landscape on gene flow. 相似文献
9.
Mansoureh Malekian Steven J. B. Cooper Kathleen M. Saint Melanie L. Lancaster Andrea C. Taylor Susan M. Carthew 《Ecology and evolution》2015,5(18):3939-3953
Ongoing habitat loss and fragmentation is considered a threat to biodiversity as it can create small, isolated populations that are at increased risk of extinction. Tree‐dependent species are predicted to be highly sensitive to forest and woodland loss and fragmentation, but few studies have tested the influence of different types of landscape matrix on gene flow and population structure of arboreal species. Here, we examine the effects of landscape matrix on population structure of the sugar glider (Petaurus breviceps) in a fragmented landscape in southeastern South Australia. We collected 250 individuals across 12 native Eucalyptus forest remnants surrounded by cleared agricultural land or exotic Pinus radiata plantations and a large continuous eucalypt forest. Fifteen microsatellite loci were genotyped and analyzed to infer levels of population differentiation and dispersal. Genetic differentiation among most forest patches was evident. We found evidence for female philopatry and restricted dispersal distances for females relative to males, suggesting there is male‐biased dispersal. Among the environmental variables, spatial variables including geographic location, minimum distance to neighboring patch, and degree of isolation were the most important in explaining genetic variation. The permeability of a cleared agricultural matrix to dispersing gliders was significantly higher than that of a pine matrix, with the gliders dispersing shorter distances across the latter. Our results added to previous findings for other species of restricted dispersal and connectivity due to habitat fragmentation in the same region, providing valuable information for the development of strategies to improve the connectivity of populations in the future. 相似文献
10.
Kevin Kit Siong Ng Soon Leong Lee Leng Guan Saw Joshua B. Plotkin Chong Lek Koh 《Tree Genetics & Genomes》2006,2(3):121-131
Analyses of the spatial distribution pattern, spatial genetic structure and genetic diversity were carried out using a 33-ha plot in a hill dipterocarp forest for three dipterocarps with different habitat preferences, i.e. Shorea curtisii on the ridges, Shorea leprosula in the valleys and Shorea macroptera both on the ridges and in the valleys. The significant spatial aggregation in small-diameter trees of all the three species was explained by limited seed dispersal. At the large-diameter trees, only S. macroptera showed random distribution and this might further prove that S. macroptera is habitat generalist, whilst S. curtisii and S. leprosula are habitat specific. The levels of genetic diversity estimated based on five microsatellite loci were high and comparable in all the three studied species. As the three studied species reproduced mainly through outcrossing, the observed high levels of genetic diversity might support the fact that the plant mating system can be used as guideline to infer the levels of genetic diversity, regardless of whether the species is habitat specific or habitat generalist. The lack of spatial genetic structure but significant aggregation in the small-diameter trees of all the three species might indicate limited seed dispersal but extensive pollen flow. Hence, if seed dispersal is restricted but pollen flow is extensive, significant spatial aggregation but no spatial genetic structure will be observed at the small-diameter trees, regardless of whether the species is habitat specific or habitat generalist. The inferred extensive pollen flow might indicate that energetic pollinators are involved in the pollination of Shorea species in the hill dipterocarp forests. 相似文献
11.
Radial Dispersion of Neighbors and the Small-Scale Competitive Impact of Two Annual Grasses on a Native Perennial Grass 总被引:1,自引:0,他引:1
In California's Mediterranean type grasslands, native perennial grasses such as Nassella pulchra are surrounded by introduced annual species and these annuals are thought to have displaced natives through much of their range. Amongst other invaders, two grasses Lolium multiflorum and Bromus hordeaceus, commonly dominate portions of the grassland with potential for N. pulchra restoration. We hypothesized that competitor species differences and small‐scale gaps (150 cm2) could be important determinants of N. pulchra survival and performance on these sites. Lolium multiflorum and B. hordeaceus were planted in 20 cm diameter circular plots at a constant rate of 1 seed per cm2 surrounding newly transplanted N. pulchra plants. Nassella pulchra showed no significant effect of the species of competitor or from the distribution of the competitors. Both interspersion of patches of bare ground and separation of competitors into patches did not increase N. pulchra pre‐dawn water potential, basal area change, number of seeds produced, or average weight of seeds. The presence of L. multiflorum was associated with a decrease in N. pulchra survival compared with plots with only B. hordeaceus. Plants with increases in basal area of less than 0.75 cm2 during the growing season had 74% mortality compared with no mortality in plants with more growth. However, initial N. pulchra plant size was not a good predictor of mortality. Limiting competition from annuals may increase survival of N. pulchra plantings, but 60% of the plants survived for at least 1 year, despite being transplanted into soil containing substantial annual grass seed. 相似文献
12.
How do steppe plants follow their optimal environmental conditions or persist under suboptimal conditions? The differing strategies of annuals and perennials
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Hocine Ait Mouheb Leila Kadik Cécile Hélène Albert Rachda Berrached Andreas Prinzing 《Ecology and evolution》2018,8(1):135-149
For a species to be able to respond to environmental change, it must either succeed in following its optimal environmental conditions or in persisting under suboptimal conditions, but we know very little about what controls these capacities. We parameterized species distribution models (SDMs) for 135 plant species from the Algerian steppes. We interpreted low false‐positive rates as reflecting a high capacity to follow optimal environmental conditions and high false‐negative rates as a high capacity to persist under suboptimal environmental conditions. We also measured functional traits in the field and built a unique plant trait database for the North‐African steppe. For both perennial and annual species, we explored how these two capacities can be explained by species traits and whether relevant trait values reflect species strategies or biases in SDMs. We found low false‐positive rates in species with small seeds, flowers attracting specialist pollinators, and specialized distributions (among annuals and perennials), low root:shoot ratios, wide root‐systems, and large leaves (perennials only) (R2 = .52–58). We found high false‐negative rates in species with marginal environmental distribution (among annuals and perennials), small seeds, relatively deep roots, and specialized distributions (annuals) or large leaves, wide root‐systems, and monocarpic life cycle (perennials) (R2 = .38 for annuals and 0.65 for perennials). Overall, relevant traits are rarely indicative of the possible biases of SDMs, but rather reflect the species' reproductive strategy, dispersal ability, stress tolerance, and pollination strategies. Our results suggest that wide undirected dispersal in annual species and efficient resource acquisition in perennial species favor both capacities, whereas short life spans in perennial species favor persistence in suboptimal environmental conditions and flowers attracting specialist pollinators in perennial and annual species favor following optimal environmental conditions. Species that neither follow nor persist will be at risk under future environmental change. 相似文献
13.
Dynamic landscape models have generally assumed random distributions of habitat although real landscapes show spatial organization
at many scales. To explore the role of spatial structure in determining the frequency of dispersal-limited forest species,
we used a cellular landscape model divided into two zones. Zones were distributed in a random, clustered, or regular spatial
pattern. Within each zone habitat cells were randomly destroyed and regenerated, and habitat density and turnover rate were
systematically varied. A hypothetical habitat-limited species dispersed between adjacent habitat cells. All trials showed
a reduced species frequency relative to a static landscape. Reduction was greater at low habitat density (P = 0.30) than at high density (0.90) suggesting the importance of habitat connectivity in controlling species frequency. The
greatest reduction occurred when habitat was concentrated in a small, regularly distributed zone at low habitat density reflecting
the enforced isolation of individual habitat cells. Very little reduction was observed when habitat cells were packed into
a small clustered zone, a situation promoting connectivity between cells. Moderate–severe frequency reduction occurred when
habitat turnover was concentrated in a clustered zone at high habitat density, but little was observed when turnover was widely
distributed in a regular or random pattern. These results can be interpreted in terms of a source-sink function in which spatial
pattern controlled the degree of contact between landscape zones and determined opportunities for dispersal between habitat
cells. We conclude that clustering of forest habitat has the potential to maintain herb species frequency in sparsely forested
landscapes. Conversely, clustering of forest disturbance in heavily forested regions, or regular distribution of forest stands
(as often occurs in agricultural regions) creates areas which are difficult to colonize, and should be avoided. 相似文献
14.
1. In fragmented landscapes many insect species depend on a regular exchange of individuals between subpopulations to ensure the persistence of the population. Thus, the ability to disperse is of particular relevance. 2. However, in some insect species mobility is not a fixed trait. Hence, knowing the causes of phenotypic plasticity is of great importance when evaluating whether a species is able to survive in fragmented landscapes or not. 3. A multi‐year field study was conducted to identify possible causes of macroptery in the wing‐dimorphic habitat specialist Metrioptera brachyptera L. and to quantify its dispersal capability (% macropters). Therefore, 746 individuals of the species were caught on 135 plots. Additionally, environmental variables that possibly induce the development of macropters (population density and habitat moisture) were recorded. 4. Dispersal capability of M. brachyptera was very low. Less than 3% were long‐winged. The statistical analysis revealed that the proportion of long‐winged M. brachyptera was strongly correlated with high bush‐cricket densities and not with habitat moisture. 5. The low dispersal capability of M. brachyptera leads to the conclusion that individual exchange between isolated populations is limited or even impossible. Habitat specialists, like M. brachyptera, may thus be unable to respond to rapid changes in the availability of suitable habitats by dispersing, and hence may be especially dependent on habitat management activities that promote the long‐term stability of existing habitat patches. 相似文献
15.
Accumulation of buried seeds and establishment of ruderal therophytic communities in disturbed habitat,central Japan 总被引:2,自引:0,他引:2
The establishment and maintenance mechanisms of pioneer communities were investigated in ruderal habitats under two disturbance regimes, frequent and infrequent cutting sites. In the infrequent cutting sites, large perennials dominated through the year and inhibited the invasion of annuals, and the perennial community succeeded to forest stage if the cutting was stopped. In the frequent cutting sites, therophytic communities of winter and summer annuals alternated by season. Fresh seeds of both winter and summer annuals are dormant, but they have different germination times and thus can share the same sites in different seasons. Wind-dispersed biennials and large perennials have nondormant seeds and easily invade the sites; however, they are unable to mature to reproductive phase due to recurrent cuttings. The therophytic species, which can complete their life-cycle in a period between cuttings, accumulate seeds in the soils and are maintained by these buried seeds (seed bank annuals) during recurrent disturbances. The seed bank is compensation for the dispersal inefficiency of seed bank annuals. After abandonment of the frequent cutting sites, the buried seeds of seed bank annuals germinate and become the first-year pioneers. Thus, seed bank annuals are not invasive colonizers but are the remnants of the ruderal weed communities before abandonment. 相似文献
16.
We investigated the scale of genetic variation of purple needlegrass (Nassella pulchra), a species commonly used in California for grassland restoration. Common garden and field data revealed evidence of genetic
differentiation between two intermixed microhabitats characterized by differences in soil depth and community composition.
We assessed the genetic variation within a single population using randomly amplified polymorphic DNA (RAPD) data collected
from clusters of five individuals in 40 locations. We found no evidence for genetic structure at the whole population level.
At smaller spatial scales, however, we found strong evidence that genetic subdivision of the population occurs at the level
of the maternal neighborhood. We suggest that the interaction between widespread pollen dispersal and restricted seed dispersal
may be the primary factor generating these results; panmictic pollen dispersal will make detection of genetic patterning difficult
at larger spatial scales while limited seed dispersal will generate local genetic structure. As a result, the detection of
population genetic structure will depend on the spatial scale of analysis. Local selection gradients related to topography
and soil depth are also likely to play a role in structuring local genetic variation. Since N. pulchra is widely used in California in grassland and woodland habitat restoration, we suggest that, as a general rule, care should
be exercised in transferring germplasm for the purposes of conservation when little is known about the within-population genetic
subdivision of a plant species.
Received: 23 December 1996 / Accepted: 20 May 1997 相似文献
17.
Protein variation in 182 Sylvilagus floridanus from 19 playa basins in Castro Co., Texas was examined using starch-gel electrophoresis. Heterozygote deficiencies were noted for all populations. This heterozygote deficiency may be due to differential selection against heterozygous individuals over the winter months. Results of F-statistics indicated a significant degree of population differentiation at six loci. Nei's genetic distance between populations ranged from 0.20 to 0.388 and a significant association between genetic distance and linear geographic distance among playas was found. These results suggest that genetic exchange and long-distance dispersal may be hindered by expanses of unsuitable habitat. 相似文献
18.
The population density and demography of five species of arctic Collembola were studied in a naturally patchy habitat, consisting
of Carex ursinae tussocks with varying degrees of isolation. Focal predictor variables were those describing the spatial configuration of
tussocks, including tussock size and isolation and the amount of habitat (cover) at a 1-m2 scale surrounding each tussock population. The Collembola populations were heavily influenced by environmental stochasticity
in the form of winter mortality and summer drought, and the influence of patchiness on population characteristics was evaluated
in this context. The five species showed very different responses to the structuring effect of the habitat, depending on life
history characteristics, mobility and habitat requirements. Population density was highly variable in both time and space.
Spring densities indicated larger winter mortality compared to observations from a previous study, and the snow- and ice-free
season from June to August only resulted in population growth for Folsomia sexoculata. In the other species, adult mortality must have been high as there was no net population growth despite observed reproduction.
The exception was Hypogastrura viatica, whose population decline was more likely to have been the result of migration out of the study area. Cover was the most
important variable explaining density. No pure area or isolation effects at the tussock level were detected, even in areas
with very low habitat cover. Drought was probably an important mortality factor, as July was particularly warm and dry. Due
to qualitative differences in the tussocks and the matrix substrate, desiccation risk would be higher during dispersal between
tussocks. We suggest that increased dispersal mortality gave the observed pattern of increased density in relation to cover,
both in general and in F. quadrioculata, an opportunistic species otherwise known for rapid population growth. Onychiurus groenlandicus, which had a similar density response to cover, may also be influenced by a rescue effect sustaining densities in areas with
high cover. The cover effect can be viewed as a large-scale factor which encompasses the general spatial neighbourhood of
each tussock, where inter-population processes are important, as opposed to internal patch dynamics.
Received: 15 March 1999 / Accepted: 22 March 2000 相似文献
19.
Germination phenology data have been collected from 75 winter annuals, 49 summer annuals, 28 monocarpic perennials, and 122 polycarpic perennials, and experimental investigations of dormancy breaking and germination requirements have been conducted on 56 winter annuals, 32 summer annuals, 18 monocarpic perennials, and 73 polycarpic perennials. The purpose of these studies was to determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species. Germination phenology is highly correlated with the responses of seeds to the yearly temperature cycle. Species with winter and summer annual life cycles have predictable germination characteristics, but monocarpic and polycarpic perennials do not. Several dormancy types may be found in a given habitat, and narrowly endemic and widely-distributed species in the same genus may have similar germination characteristics. Within some families there is a tendency for a particular type of seed-temperature response to be very important, but frequently this is related to the predominance of a given life cycle type in the family. 相似文献
20.
Intrinsic factors drive spatial genetic variation in a highly vagile species,the wedge‐tailed eagle Aquila audax,in Tasmania
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Christopher P. Kozakiewicz Scott Carver Jeremy J. Austin Jill M. Shephard Christopher P. Burridge 《Journal of avian biology》2017,48(7):1025-1034
Knowledge of dispersal in a species, both its quantity and the factors influencing it, are crucial for our understanding of ecology and evolution, and for species conservation. Here we quantified and formally assessed the potential contribution of extrinsic factors on individual dispersal in the threatened Tasmanian population of wedge‐tailed eagle Aquila audax. As successful breeding by these individuals appears strongly related to habitat, we tested the effect of landscape around sampling sites on genetic diversity and spatial genetic variation, as these are influenced by patterns of dispersal. Similarly, we also tested whether habitat intervening sampling sites could explain spatial genetic variation. Twenty microsatellites were scored, but only a small proportion of spatial genetic variation (4.6%) could be explained by extrinsic factors, namely habitat suitability and elevation between sites. However, significant clinal genetic variation was evident across Tasmania, which we explain by intrinsic factors, likely high natal philopatry and occasional long‐distance dispersal. This study demonstrates that spatial genetic variation can be detected in highly vagile species at spatial scales that are small relative to putative dispersal ability, although here there was no substantial relationship with landscape factors tested. 相似文献