首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
We studied selection by predators for cryptic prey coloration in a visually heterogeneous habitat that consists of two microhabitats. It has been suggested that the probability of escaping detection in such habitats might be optimized by maximizing crypsis in one of the microhabitats. However, a recent model indicates that a coloration that compromises the requirements of different microhabitats might sometimes be the optimal solution. To experimentally study these hypotheses, we allowed great tits (Parus major L.) to search for artificial prey items in two different microhabitats (background boards): small patterned and large patterned. On each board there was one prey item that was either small-patterned, large-patterned or medium-patterned and thus compromised. Search time was used as the measure of crypsis and was on average longer on the large-patterned than on the small-patterned background. On the small-patterned background, the small-patterned prey was more cryptic than the compromised prey, which was in turn more cryptic than the large-patterned prey. On the large-patterned background, the small-patterned prey was least cryptic, but the compromised prey did not differ significantly from the large-patterned prey. The compromised coloration had lower predation risk than the matching colorations. This indicates that in some conditions a compromised coloration might be the best strategy for the prey and has important implications for the study of animal coloration.  相似文献   

3.
Cryptic prey coloration typically bears a resemblance to the habitat the prey uses. It has been suggested that coloration which visually matches a random sample of the background maximizes background matching. We studied this previously untested hypothesis, as well as another, little studied principle of concealment, disruptive coloration, and whether it could, acting in addition to background matching, provide another plausible means of achieving camouflage. We presented great tits (Parus major) with artificial background-matching and disruptive prey (DP), and measured detection times. First, we studied whether any random sample of a background produces equally good crypsis. This turned out to not be the case. Next, we compared the DP and the best background-matching prey and found that they were equally cryptic. We repeated the tests using prey with all the coloration elements being whole, instead of some of them being broken by the prey outline, but this did not change the result. We conclude that resemblance of the background is an important aspect of concealment, but that coloration matching a random visual sample of the background is neither sufficient nor necessary to minimize the probability of detection. Further, our study lends empirical support to the principle of disruptive coloration.  相似文献   

4.
Optimization of cryptic coloration in heterogeneous habitats   总被引:3,自引:0,他引:3  
We present a theoretical approach to the optimization of crypsis in heterogeneous habitats. Our model habitat consists of two different microhabitats, and the optimal combination of crypsis in the microhabitats is supposed to maximize the probability of escaping detection by a predator. The probability of escaping detection for a prey is a function of: (i)degree of crypsis, (ii) probability of occurrence in the microhabitats and (iii) probability of encountering a predator in the microhabitats. Because crypsis is background-specific there is a trade-off between crypsis in two visually different microhabitats. Depending on the nature of the trade-off, the optimal coloration is either a compromise between the requirements of the differing microhabitats or entirely adapted to only one of them. An increased risk of predation in one of the microhabitats favours increased crypsis in that microhabitat. Because the trade-off constrains possible optimal solutions, it is not possible to predict the optimal coloration only from factors (i)-(iii). However, habitat choice may fundamentally change the situation. If minimizing predation risk does not incur any costs, the prey should exclusively prefer the microhabitat where it has a lower probability of encountering a predator and better crypsis. The implications of these results for variation in cryptic coloration and polymorphism are discussed.  相似文献   

5.
In psychological studies of visual perception, symmetry is accepted as a potent cue in visual search for cryptic objects, yet its importance for non-human animals has been assumed rather than tested. Furthermore, while the salience of bilateral symmetry has been established in laboratory-based search tasks using human subjects, its role in more natural settings, closer to those for which such perceptual mechanisms evolved, has not, to our knowledge, been investigated previously. That said, the salience of symmetry in visual search has a plausible adaptive rationale, because biologically important objects, such as prey, predators or conspecifics, usually have a plane of symmetry that is not present in their surroundings. We tested the conspicuousness to avian predators of cryptic artificial, moth-like targets, with or without bilateral symmetry in background-matching coloration, against oak trees in the field. In two independent experiments, symmetrical targets were predated at a higher rate than otherwise identical asymmetrical targets. There was a small, but significant, fitness cost to symmetry in camouflage patterns. Given that birds are the most commonly invoked predators shaping the evolution of defensive coloration in insects, this raises the question of why bilateral asymmetry is not more common in cryptic insects.  相似文献   

6.
Carotenoids are used for many functions by animals, including combining with other pigments to produce aposematic and cryptic coloration. Carotenoids in combination with blue pigments are responsible for green coloration in many caterpillars, and thus carotenoid sequestration may reduce their contrast against a green foliage background. We tested the hypothesis that carotenoid sequestration reduces contrast and enhances survival by rearing Trichoplusia ni Hübner (Lepidoptera: Noctuidae) on Brassica oleracea L. var. Acephala (Brassicaceae) leaves and exposing them to predators. We found that carotenoids derived from the host plant are partially excreted, along with chlorophyll, but also sequestered in hemolymph. Larvae that were given plants that provided carotenoids showed less contrast against their host plants within 1 day compared to larvae that were not provided with carotenoids. Last, both short‐term field observations and laboratory trials of larvae caged with predatory Podisus maculiventris Say (Hemiptera: Pentatomidae) nymphs showed that survival of carotenoid‐sequestering larvae was higher compared to larvae that did not sequester. These results suggest that carotenoid sequestration may be an important adaptive strategy that reduces susceptibility to natural enemies that hunt by sight. Further research that examines the mechanisms by which carotenoids are absorbed and modified will lend insights into the evolution of carotenoids functioning as passive defensive compounds.  相似文献   

7.
8.
It is well known that predators often influence the foraging behaviour of prey through the so-called “fear effect”. However, it is also possible that predators could change prey behaviour indirectly by altering the prey’s food supply through a trophic cascade. The predator–sea urchin–kelp trophic cascade is widely assumed to be driven by the removal of sea urchins by predators, but changes in sea urchin behaviour in response to predators or increased food availability could also play an important role. We tested whether increased crevice occupancy by herbivorous sea urchins in the presence of abundant predatory fishes and lobsters is a response to the increased risk of predation, or an indirect response to higher kelp abundances. Inside two New Zealand marine reserves with abundant predators and kelp, individuals of the sea urchin Evechinus chloroticus were rarer and remained cryptic (i.e. found in crevices) to larger sizes than on adjacent fished coasts where predators and kelp are rare. In a mesocosm experiment, cryptic behaviour was induced by simulated predation (the addition of crushed conspecifics), but the addition of food in the form of drift kelp did not induce cryptic behaviour. These findings demonstrate that the ‘fear’ of predators is more important than food availability in promoting sea urchin cryptic behaviour and suggest that both density- and behaviourally mediated interactions are important in the predator–sea urchin–kelp trophic cascade.  相似文献   

9.
Nest predation highly determines the reproductive success in birds. In agricultural grasslands, vegetation characteristics and management practices influences the predation risk of ground breeders. Little is known so far on the predation pressure on non-passerine nests in tall swards. Investigations on the interaction of land use with nesting site conditions and the habitat selection of nest predators are crucial to develop effective conservation measures for grassland birds.In this study, we used artificial nests baited with quail and plasticine eggs to identify potential predators of ground nests in floodplain meadows and related predation risk to vegetation structure and grassland management.Mean daily predation rate was 0.01 (±0.012) after an exposure duration of 21 days. 70% of all observed nest predations were caused by mammals (Red Fox and mustelids) and 17.5% by avian predators (corvids). Nest sites close to the meadow edge and those providing low forb cover were faced with a higher daily predation risk. Predation risk also increased later in the season. Land use in the preceding year had a significant effect on predation risk, showing higher predation rates on unmanaged sites than on mown sites. Unused meadows probably attract mammalian predators, because they provide a high abundance of small rodents and a more favourable vegetation structure for foraging, increasing also the risk of incidental nest predations. Although mowing operation is a major threat to ground-nesting birds, our results suggest that an annual removal of vegetation may reduce predation risk in the subsequent year.  相似文献   

10.
Agricultural intensification is an important driver of biodiversity decline. Regarding grassland ecosystems, traditionally managed hay meadows, as opposed to highly productive silage grassland, are often of high conservation value. Here, we compare spider assemblages among five grassland management regimes along an intensification gradient, ranging from long-term fallows (not farmed for ≥ 30 years) via traditionally managed hay meadows to high-intensity silage grassland. Humid long-term fallows harboured highest species richness and diversity, and their assemblages differed strongly from other management regimes. There was surprisingly little variation though among different types of hay meadows and silage grassland. We also included environmental parameters and land-cover types in the surroundings of study sites, indicating that spider assemblages were most strongly shaped by fallow-related parameters and the proportion of forests. The high spider diversity on fallows may result from their undisturbed vegetation structure, while management, regardless of frequency, may have detrimental effects. Our results demonstrate the high importance of unmanaged areas even in regions with an overall low land-use intensity, such as grassland ecosystems. We thus recommend the inclusion of temporal grassland fallows (unmanaged for 3-5 years) in agri-environmental schemes to increase landscape heterogeneity and preserve spider diversity.  相似文献   

11.
Although forest stands represent 47% of the total land area in Europe, alterations to the forest habitat through logging and plantation of exotic trees has led to significant changes in forest biocenoses. Due to their peculiar biology and life history, epiphytic bryophytes, which include a number of species of high conservation value, are especially concerned. Ordinal logit regression was used to test whether trends in diversity and abundance of obligate epiphytic bryophytes are explained by forest cover and spruce plantation and determine specific optima and degree of reliance to these factors at the landscape scale. Spruce plantations had a negative impact on both species diversity and abundance. Although large forest patches were important for a set of species exclusively or more frequently occurring under the forest cover, the abundance of a number of species previously identified as woodland bryophytes decreased or was uncorrelated with increasing forest cover. Furthermore, the species pool adapted to edge-related abiotic conditions was important. The global epiphytic diversity did consequently not decrease with decreasing forest cover at the landscape scale. If large forest patches are important for the conservation of a set of species exclusively or more frequently occurring under the forest cover, the conservation of epiphytic bryophytes thus also involves the conservation of pioneer trees in open landscapes. A series of management measures, which may help maximize the species diversity and probability of occurrence of key-species of high conservation interest, are proposed.  相似文献   

12.
Characterizing the effects of landscape features on genetic variation is essential for understanding how landscapes shape patterns of gene flow and spatial genetic structure of populations. Most landscape genetics studies have focused on patterns of gene flow at a regional scale. However, the genetic structure of populations at a local scale may be influenced by a unique suite of landscape variables that have little bearing on connectivity patterns observed at broader spatial scales. We investigated fine-scale spatial patterns of genetic variation and gene flow in relation to features of the landscape in desert tortoise (Gopherus agassizii), using 859 tortoises genotyped at 16 microsatellite loci with associated data on geographic location, sex, elevation, slope, and soil type, and spatial relationship to putative barriers (power lines, roads). We used spatially explicit and non-explicit Bayesian clustering algorithms to partition the sample into discrete clusters, and characterize the relationships between genetic distance and ecological variables to identify factors with the greatest influence on gene flow at a local scale. Desert tortoises exhibit weak genetic structure at a local scale, and we identified two subpopulations across the study area. Although genetic differentiation between the subpopulations was low, our landscape genetic analysis identified both natural (slope) and anthropogenic (roads) landscape variables that have significantly influenced gene flow within this local population. We show that desert tortoise movements at a local scale are influenced by features of the landscape, and that these features are different than those that influence gene flow at larger scales. Our findings are important for desert tortoise conservation and management, particularly in light of recent translocation efforts in the region. More generally, our results indicate that recent landscape changes can affect gene flow at a local scale and that their effects can be detected almost immediately.  相似文献   

13.
Forest patches with high biological value are protected as woodland key habitats (WKH), which are identified by the presence of forest structures and indicator species. However, management for conservation needs to consider also managed forests as habitats for species. In this respect, there is a need to set quantitative targets for species and structures at different landscape scales. Due to non-intensive methods of forest management used prior to 1940 in Latvia, it might be expected that large areas of forest have developed structures that can support many species characteristic of natural forests. The aim of the study was to create a model that best described the richness of bryophyte species that are characteristic of natural forests, using forest structures as explanatory factors. The structures and bryophyte communities on living trees and coarse woody debris (CWD) were described in plots along transects blindly placed in areas dominated by State forests under commercial management. Explanatory variables related to tree species composition and tree size explained 54% of the variation in WKH indicator species richness on living trees. The best explanatory factors were maximum diameter of deciduous tree species and CWD. Low richness of total bryophyte and indicator species was found on dead wood, and the amount of variation in bryophyte species richness on CWD explained by explanatory variables was low. The study indicates the importance of deciduous tree substrate in managed forests in maintaining the spatial continuity of epiphytic species diversity. However, the forests in the managed forest landscape did not support high diversity of epixylic species, even in the WKHs, due to low diversity of suitable dead wood substrate.  相似文献   

14.
Applying natural forestry concepts in an intensively managed landscape   总被引:2,自引:0,他引:2  
Near-to-nature forestry is an attractive concept, but it is difficult to apply in a landscape where (i) the remaining fragments of original-natural forests are small and far apart; (ii) most large forests are secondary and very artificial; (iii) long-naturalized trees and other forest species are present throughout the country, and; (iv) natural disturbance regimes and their consequences cannot readily be observed. This paper summarizes the issues and problems relating to ancient seminatural woods and conifer plantation forests in Britain. Measures are indicated that would bring their management nearer to nature. Natural elements can be incorporated into stand composition, stand structure, processes and patterns, provided general principles are interpreted in a pragmatic and flexible manner.  相似文献   

15.
The adaptive significance of cryptic colour patterns has seldom been analysed in a phylogenetic context. We mapped data on the presence vs. absence of dorsal stripes, and the use of needle-like vs. broad foliage, onto a recent phylogeny of Timema walking-sticks, in order to infer the evolutionary history of these traits and test the hypothesis that the dorsal stripe is an adaptation for crypsis on needle-like leaves. By maximum parsimony optimization, the dorsal stripe has evolved five or six times in this clade, each time in association with the use of vegetation with needle-like leaves. Maddison's concentrated changes test showed that this association between morphology and habitat was statistically significant. By contrast, results based on Pagel's maximum likelihood analyses did not reach significance, probably because the large number of origins of dorsal stripe introduces statistical uncertainty. These results suggest that the adaptations for crypsis can arise readily and in parallel, in the appropriate selective environment. However, they may also constrain the evolution of host-plant use, as there is no unambiguous case of Timema species with dorsal stripes shifting to broad-leaved plants.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 1–5.  相似文献   

16.
Predation is one of the most important interactions between species and a major selection pressure in wild mammal populations. Camouflage is a common pattern of colorations resulting from predation pressure, however, atypical coloration may appear in the wild. Both predation and atypical coloration in mammal species are difficult to observe in a natural setting but contain important biological information. Here we describe a leucistic tayra (Eira barbara) attempting to prey on a sloth (Bradypus tridactylus). The event occurred in Brazilian Central Amazon as a tayra unsuccessfully tried to kill an adult sloth in the mid-canopy of a secondary forest.  相似文献   

17.
Box turtles are being extirpated from much of their former range and remaining populations often live in association with anthropogenically altered habitats. This is particularly evident at the northern distributional limit of eastern box turtles (Terrapene carolina carolina) and is an important factor to consider during the winter months when their ability to respond to microclimatic change is limited. Using temperature dataloggers, we studied the hibernal microclimate of box turtles and associated habitat following timber harvests. We monitored the body temperatures of 38 eastern box turtles and collected detailed air and soil profile temperatures of 12 box turtle hibernacula, 6 clearcuts, and 6 adjacent forested areas during the hibernal season (winter 2009–2010). We partitioned the hibernal season into 2 biologically significant thermal periods: hibernation and emergence. The mean hibernation body temperature averaged (3.28° C, SE = 0.09) and corresponded to an average depth of 10 cm. Clearcuts were consistently colder ( = 1.91° C) than forests ( = 2.68° C) and hibernacula ( = 2.77° C) during hibernation, but became the warmest areas during emergence ( = 9.96° C). We found that in the average clearcut, turtles could burrow to approximately 20 cm to attain the average hibernation body temperature or to approximately 15 cm to attain a body temperature no different than those overwintering on colder, northeast-facing slopes in the forest ( = 2.83° C). Alternatively, we found that southwest-facing slopes were warmer and if turtles chose to overwinter only in clearcuts on those slopes, they could remain shallower. All but 1 turtle overwintered in forested areas; however, our study suggests that some timber harvested areas offer various microhabitats exploitable by hibernating box turtles based on soil profile temperatures, slope aspect, and depth of hibernation. © 2012 The Wildlife Society.  相似文献   

18.
Urbanization is a key global driver in the modification of land use and has been linked to population declines even in widespread and relatively common species. Cities comprise a complex assortment of habitat types yet we know relatively little about the effects of their composition and spatial configuration on species distribution. Although many bat species exploit human resources, the majority of species are negatively impacted by urbanization. Here, we use data from the National Bat Monitoring Programme, a long‐running citizen science scheme, to assess how two cryptic European bat species respond to the urban landscape. A total of 124 × 1 km2 sites throughout Britain were surveyed. The landscape surrounding each site was mapped and classified into discrete biotope types (e.g., woodland). Generalized linear models were used to assess differences in the response to the urban environment between the two species, and which landscape factors were associated with the distributions of P. pipistrellus and P. pygmaeus. The relative prevalence of P. pygmaeus compared to P. pipistrellus was greater in urban landscapes with a higher density of rivers and lakes, whereas P. pipistrellus was frequently detected in landscapes comprising a high proportion of green space (e.g., parklands). Although P. pipistrellus is thought to be well adapted to the urban landscape, we found a strong negative response to urbanization at a relatively local scale (1 km), whilst P. pygmaeus was detected more regularly in wooded urban landscapes containing freshwater. These results show differential habitat use at a landscape scale of two morphologically similar species, indicating that cryptic species may respond differently to anthropogenic disturbance. Even species considered relatively common and well adapted to the urban landscape may respond negatively to the built environment highlighting the future challenges involved in maintaining biodiversity within an increasingly urbanized world.  相似文献   

19.
The occurrence of coral snake coloration among unrelated venomous and non‐venomous snake species has often been explained in terms of warning coloration and mimicry. In Argentina, no field tests have been conducted to confirm this mimetic association between one venomous coral species (Micrurus phyrrocryptus, Elapidae) and two non‐venomous snake species with a similar color pattern (Lystrophis pulcher and Oxyrhopus rhombifer, Colubridae). The aims of this work were to test for the possible aposematic or cryptic function of the ring pattern and coloration of coral snakes and false coral snakes from central Argentina, and to analyse whether the pattern is effective throughout the year. Predation on snakes was estimated by using non‐toxic plasticine replicas of ringed venomous and non‐venomous snakes and unbanded green snakes placed along transects in their natural habitat during the dry and rainy season. Ringed color pattern was attacked by predators despite the background color. One of the replica types was attacked more than expected during the dry season, suggesting that both shape and width of rings may influence the choice by predators. The reaction of predators towards replicas that mimic snake species with ringed patterns is independent of the geographical region, and we can conclude that mimicry characteristics are quite general when the true models are present in the area.  相似文献   

20.

Questions

Near-ground temperatures can vary substantially over relatively short distances, enabling species with different temperature preferences and geographical distributions to co-exist within a small area. In a forest landscape, the near-ground temperatures may change due to management activities that alter forest density. As a result of such management activities, current species distributions and performances might not only be affected by current microclimates, but also by past conditions due to time-lagged responses.

Location

Sweden.

Methods

We examined the effects of past and current microclimates on the distributions and performances of two northern, cold-favoured, and two southern, warm-favoured, plant species in 53 managed forest sites. Each pair was represented by one vascular plant and one bryophyte species. We used temperature logger data and predictions from microclimate models based on changes in basal area to relate patterns of occurrence, abundance, and reproduction to current and past microclimate.

Results

The two northern species were generally favoured by microclimates that were currently cold, characterised by later snowmelt and low accumulated heat over the growing season. In contrast, the two southern species were generally favoured by currently warm microclimates, characterised by high accumulated heat over the growing season. Species generally had higher abundance in sites with a preferred microclimate both in the past and present, and lower abundance than expected from current conditions, if the past microclimate had changed from warm to cold or vice versa, indicating time-lags in abundance patterns of the species.

Conclusions

Our results show a potential importance of past and present microclimate heterogeneity for the co-existence of species with different temperature preferences in the same landscape and highlight the possibility to manage microclimates to mitigate climate change impacts on forest biodiversity.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号