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1.
While spatial synchrony of oscillating populations has been observed in many ecological systems, the causes of this phenomenon are still not well understood. The most common explanations have been the Moran effect (synchronous external stochastic influences) and the effect of dispersal among populations. Since ecological systems are typically subject to large spatially varying perturbations which destroy synchrony, a plausible mechanism explaining synchrony must produce rapid convergence to synchrony. We analyze the dynamics through time of the synchronizing effects of dispersal and, consequently, determine whether dispersal can be the mechanism which produces synchrony. Specifically, using methods new to ecology, we analyze a two patch predator-prey model, with identical weak dispersal between the patches. We find that a difference in time scales (i.e. one population has dynamics occurring much faster than the other) between the predator and prey species is the most important requirement for fast convergence to synchrony.  相似文献   

2.
Recently, interest in species abundance (SAD) distributions has been revived by introduction of a new model, the zero-sum multinomial (ZSM). Yet detailed statistical analyses show that the model does not differ from the lognormal distribution proposed in the 1940s. These analyses were based on data from tropical trees where all individuals in a defined area were identified to species. For many ecological data sets it is not possible to identify and count all individuals in a given area. Here we compare data on marine benthos and fish assemblages with data on terrestrial microfauna and ants. We show that these assemblages show similar SAD patterns and that the SADs are best described by a two-group lognormal model. Whereas the 2-group model fitted all data sets the single group model fitted all except the tropical rainforest ants. However, tests comparing the fits to the 2-group versus the single lognormal model showed that the 2-group model was a significantly better fit to the fish and insect data. The two groups are of rare and common species and the rare group dominates in all four data sets. We suggest that the reason for this is that rare species are continuously immigrating from outside the sampled area. Data on tropical tree assemblages where complete accounts were made do not show such high dominance of rare species where the sampled area is large. We conclude that SAD patterns are similar in marine and terrestrial systems that are open to immigration and that the lognormal distribution is still a valid model for SADs.  相似文献   

3.
1. Dispersal is a crucial process in maintaining population structures in many organisms, and is hypothesized as a process underlying the interspecific relationship between abundance and distribution. Here we examined whether there was a link between the dispersal and developmental modes of marine macroinvertebrates and the slopes and elevations of interspecific abundance-occupancy relationships. We predicted that if within-site retention of larvae ranks in the order brooders > lecithotrophs > planktotrophs, for any given level of mean abundance, occupancy should increase in the order brooders < lecithotrophs < planktotrophs. We also predicted that propensity to form metapopulations should be greater for planktonic dispersers (i.e. lecithotrophs and planktotrophs combined) than for non-planktonic (i.e. brooders), resulting in steeper abundance-occupancy relationships for the former. 2. Predictions were tested using a data set for 362 subtidal marine macroinvertebrates occurring across 446 1-km(2) grid squares around the British Isles; analyses were performed on the data set as a whole and for separate phyla. 3. The total data set had a Z-transformed effect size of 0.79, within the confidence intervals described by Blackburn et al. (2006; Journal of Animal Ecology, 75, 1426-1439), and was consistently present with relatively homogeneous effect size in separate analyses of polychaetes, crustaceans, molluscs and echinoderms. 4. In all cases, planktonic dispersing organisms showed an abundance-occupancy relationship with greater elevation than that for non-planktonic organisms; in polychaetes the elevation of slopes was in the rank order planktotrophs > lecithotrophs > brooders. No differences between the slopes of the abundance-occupancy relationship were apparent for different dispersal modes either within, or across phyla. 5. We conclude that dispersal capacity may play an important part in determining the elevation of the abundance-occupancy relationship, the corollary of low dispersal in the marine realm being greater local retention of larvae and greater local population abundance at low extents of geographical distribution.  相似文献   

4.
Galaxias maculatus is one of the world's most widely distributed freshwater fish. This species has a marine-tolerant juvenile phase, and a geographical range extending through much of the southern hemisphere. We conducted phylogeographic analyses of 163 control region haplotypes of G. maculatus, including samples from New Zealand (five locations), Tasmania (one location) and Chile (one location). A lack of genetic structure among New Zealand samples suggests that marine dispersal facilitates considerable gene flow on an intra-continental scale. The discovery of a Tasmanian-like haplotype in one of 144 New Zealand samples indicates that inter-continental marine dispersal occurs but is insufficient to prevent mitochondrial DNA differentiation among continents. The sister relationship of Tasmanian and New Zealand clades implies that marine dispersal is an important biogeographical mechanism for this species. However, a vicariant role in the divergence of eastern and western Pacific G. maculatus cannot be rejected.  相似文献   

5.
The quantity of seeds dispersed is considered one of several means to determine the dispersal effectiveness of an animal. However, there is little consistency in the manner in which quantities are measured or presented. Here, we quantify seed dispersal by white-faced capuchin monkeys (Cebus capucinus) in Santa Rosa National Park, Costa Rica by measuring: degree of frugivory, number of plant species consumed, the number of seeds consumed per unit time, the number of seeds dispersed intact per unit time, and the number of seeds dispersed intact per unit space. Forty-nine percent of C. capucinus diet is composed of the fruit of 39 species, 4 of which constitute 82% of the frugivory. Seventy-four percent of consumed fruits contain seeds that pass intact through the capuchin digestive system. Capuchins pass a mean of 15.7 seeds of a mean of 1.3 species per defecation, and defecate 25.4 times per 12-h day. These numbers are compared with extant data for C. capucinus, and possible reasons for discrepancies among results between studies are discussed. We propose a standardization of quantitative measures of seed dispersal so that quantifications of seed dispersal can be compared within species, and eventually across species.  相似文献   

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What is the required minimum landscape size for dispersal studies?   总被引:2,自引:0,他引:2  
Among small animals dispersal parameters are mainly obtained by traditional methods using population studies of marked individuals. Dispersal studies may underestimate the rate and distance of dispersal, and be biased because of aggregated habitat patches and a small study area. The probability of observing long distance dispersal events decreases with distance travelled by the organisms. In this study a new approach is presented to solve this methodological problem. An extensive mark-release-recapture programme was performed in an area of 81 km(2) in southern Sweden. To estimate the required size of the study area for adequate dispersal measures we examined the effect of study area size on dispersal distance using empirical data and a repeated subsampling procedure. In 2003 and 2004, two species of diurnal burnet moths (Zygaenidae) were studied to explore dispersal patterns. The longest confirmed dispersal distance was 5600 m and in total 100 dispersal events were found between habitat patches for the two species. The estimated dispersal distance was strongly affected by the size of the study area and the number of marked individuals. For areas less than 10 km(2) most of the dispersal events were undetected. Realistic estimates of dispersal distance require a study area of at least 50 km(2). To obtain adequate measures of dispersal, the marked population should be large, preferably over 500 recaptured individuals. This result was evident for the mean moved distance, mean dispersal distance and maximum dispersal distance. In general, traditional dispersal studies are performed in small study areas and based on few individuals and should therefore be interpreted with care. Adequate dispersal measures for insects obtained by radio-tracking and genetic estimates (gene flow) is still a challenge for the future.  相似文献   

8.
When is breeding for drought tolerance optimal if drought is random?   总被引:3,自引:0,他引:3  
* Increasing climatic unpredictability associated with characteristics of some species makes plant drought-tolerance an important drought-adaptation strategy. Using norm-of-reaction functions, or empirically determined functions that enable us to predict the state of a trait given the state of an environmental variable, allows modelling of plant performance when water availability varies randomly. * A mathematical model is proposed to evaluate drought-tolerance and growth strategies given a set of environmental parameters: the frequency of rainy days, the soil water-storage capacity, plant water use and plant growth rates. This model compares the performance of genotypes that differ in drought tolerance expressed as the ability to grow in drier soils, and assumes a general trade-off function between drought tolerance and maximum plant growth rate. * It is worth selecting plants with a greater degree of drought tolerance, expressed by the ability to grow in drier soils whenever the frequency of rains is smaller than the rate of soil water depletion. Otherwise, maximizing growth rate at the expense of drought tolerance is the best strategy. The nature of the trade-off between drought tolerance and plant growth rate also constrains the selection for optimal drought-adapted genotypes. * Breeders will have to consider these aspects of plant-environment interactions before establishing selection programs for drought adaptation.  相似文献   

9.
When is pressure osmotic?   总被引:1,自引:0,他引:1  
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10.
Summary Terrestrial and freshwater pulmonate snails exhibit a marked depression of aerobic metabolism during estivation. This is an adaptation for existence in periodically harsh environments and, though marine gastropods may undergo anaerobic metabolism, they have not been shown to adaptively depress aerobic metabolic rate. We compared the metabolic response to progressive aerial exposure of two intertidal gastropod limpets, a prosobranch and a pulmonate. The prosobranch Patella granularis maintained a constant heart rate until shortly before death. In contrast, the pulmonate Siphonaria oculus underwent facultative depression of heart rate, accompanied by a decline in oxygen consumption. Both heart rate and oxygen consumption returned to normal levels on reimmersion in water. Metabolic rate depression is energy conserving, and may account for the ability of S. oculus to extend higher up the shore than P. granularis, into areas where food availability is low. S. oculus is a primitive, marine pulmonate, periodically subject to harsh conditions, and its capacity for metabolic rate depression may represent a pre-adaptation for life on land.  相似文献   

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Mammalian terrestrial locomotion has many unifying principles. However, the Macropodoidea are a particularly interesting group that exhibit a number of significant deviations from the principles that seem to apply to other mammals. While the properties of materials that comprise the musculoskeletal system of mammals are similar, evidence suggests that tendon properties in macropodoid marsupials may be size or function dependent, in contrast to the situation in placental mammals. Postural differences related to hopping versus running have a dramatic effect on the scaling of the pelvic limb musculoskeletal system. Ratios of muscle fibre to tendon cross-sectional areas for ankle extensors and digital flexors scale with positive allometry in all mammals, but exponents are significantly higher in macropods. Tendon safety factors decline with increasing body mass in mammals, with eutherians at risk of ankle extensor tendon rupture at a body mass of about 150 kg, whereas kangaroos encounter similar problems at a body mass of approximately 35 kg. Tendon strength appears to limit locomotor performance in these animals. Elastic strain energy storage in tendons is mass dependent in all mammals, but exponents are significantly larger in macropodid. Tibial stresses may scale with positive allometry in kangaroos, which result in lower bone safety factors in macropods compared to eutherian mammals.  相似文献   

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Although genes have specific phenotypic consequences in a given species, this functional relationship can clearly change during the course of evolution. Many cases of evolutionary dissociations between homologous genes and homologous morphological features are now known. These dissociations have interesting and important implications for understanding the genetic basis for evolutionary change in morphology.  相似文献   

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Lipids are of increasing importance in understanding biological systems. Lipids carrying an anionic charge are noted in particular for their electrostatic interactions with both proteins and divalent cations. However, the biological, analytical, chemical and biophysical data of such species are rarely considered together, limiting our ability to assess the true role of such lipids in vivo. In this review, evidence from a range of studies about the lipid phosphatidylglycerol is considered. This evidence supports the conclusions that this lipid is ubiquitous in living systems and generally of low abundance but probably fundamental for terrestrial life. Possible reasons for this are discussed and further questions posed.  相似文献   

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