关键词： Phylogenetics   molecular clock   sequence evolutionary rate   phenotypic evolution   morphology   genomics  

摘要： Sequence evolution behaves in a relatively consistent manner, leading to one of the fundamental paradigms in biology, the existence of a 'molecular clock'. The molecular clock can be distilled to the concept of accumulation of substitutions, through time yielding a stable rate from which we can estimate lineage divergence. Over the last 50 years, evolutionary biologists have obtained an in-depth understanding of this clock's nuances. It has been fine-tuned by taking into account the vast heterogeneity in rates across lineages and genes, leading to 'relaxed' molecular clock methods for timetree reconstruction. Sequence rate varies with life history traits including body size, generation time and metabolic rate, and we review recent studies on this topic. However, few studies have explicitly examined correlates between molecular evolution and morphological evolution. The patterns observed across diverse lineages suggest that rates of molecular and morphological evolution are largely decoupled. We discuss how identifying the molecular mechanisms behind rapid functional radiations are central to understanding evolution. The vast functional divergence within mammalian lineages that have relatively 'slow' sequence evolution refutes the hypotheses that pulses in diversification yielding major phenotypic change are the result of steady accumulation of substitutions. Patterns rather suggest phenotypic divergence is likely caused by regulatory alterations mediated through mechanisms such as insertions/deletions in functional regions. These can rapidly arise and sweep to fixation faster than predicted from a lineage's sequence neutral substitution rate, enabling species to leapfrog between phenotypic 'islands'. We suggest research directions that could illuminate mechanisms behind the functional diversity we see today.

关键词： Ecological modeling   Alien species   Classification trees   Azolla filiculoides (Lam.)  

摘要： Alien species have the abilities to alter the ecosystems they invade. We used classification trees (CTs) to predict the distribution of an exotic species, Azolla filiculoides (Lam.), at Selkeh Wildlife Refuge located in Anzali wetland, northern Iran. Cover percentages of Azolla were modeled using 33 physico-chemical and structural habitat variables. In total, 7 sampling sites were considered for abiotic and biotic sampling which resulted in 84 datasets. The predictive power of CTs was assessed based on two performance criteria: the percentage of Correctly Classified Instances (CCI %) and Cohen's kappa statistics (kappa). Different Pruning Confidence Factors (PCFs) were tested in order to improve the predictive results with regard to the complexity and accuracy of the predictions. The obtained results showed that Azolla distribution prediction was reliable in terms of both performance criteria (CCI > 70% and kappa > 0.40). Of the 33 variables presented to the model, the validity of 9 variables was confirmed for the prediction of habitat requirement of Azolla. A logical relationship was found between the distribution of Azolla and structural habitat variables such as air temperature, humidity, light intensity and depth of wetland. Besides, orthophosphate and nitrate were found to be two important nutrients for the prediction. The CTs allowed the selection of the most important variables and thus provided critical information to support the implementation of an Azolla management programme in Anzali wetland. More specifically, this kind of models can be used to select parameters that should be sampled at Selkeh wetland in the future. (C) 2012 Elsevier B.V. All rights reserved.

关键词： fire ecology   invertebrates   Kimberley   savanna  

摘要： This paper documents the effects of fire on grass-layer invertebrates in tropical savannas of the Kimberley region of north-western Australia, in the context of resource availability for consumers. Inappropriate fire regimes have been identified as a factor threatening a number of vertebrate groups, including small mammals, across northern Australia, and a possible mechanism might be through the effects of individual fires or fire regimes on food availability. We test for a fire effect on grass-layer invertebrate resources, which may affect insectivorous savanna vertebrates. Wet season sweep-net invertebrate samples were taken in two tropical savanna habitats, with contrasting laterite and sandstone substrates, in 2008, 2009 and 2010. Sites were stratified by post-fire interval to analyse invertebrate successional change after fire. In addition, experimental burns were implemented in 2010 to investigate immediate post-fire invertebrate responses. Total invertebrate numbers declined by 8090% immediately (1 week) following fire, reflecting the loss of grass-layer habitat. Of the commonly sampled invertebrate groups, Araneae, Coleoptera, Hempitera, Lepidoptera, Formicidae and Diptera were all reduced in numbers immediately post-fire, whereas Orthoptera showed no immediate post-fire decline. Invertebrate numbers were rapidly restored to pre-fire levels by the first wet season after fire, and no detectible change was observed in numbers or composition from 1 to 34 years post-fire (the longest post-fire interval available). This suggests that the effects of individual fires on grass-layer invertebrates are very short-lived. Such short-lived post-fire responses among grass-layer invertebrates, plus evidence that most ground-layer invertebrate groups are fire-resilient, suggest that food resource limitation is not a tenable explanation for fire-related declines among insectivorous savanna vertebrates. However, wet season burning could result in significant invertebrate reso

关键词： mammals   monitoring   abundance   population cycle  

摘要： The population dynamics of Clethrionomys voles has a cyclic pattern characteristic of these rodents in Scandinavia (Koshkina, 1966; Okulova and Kataev, 2003; Stenseth, 1999). Among 16 population cycles traced in Cl. rufocanus, there were eight cycles with a 4 year period, six with a 6 year period, and two with a 6 year period.

关键词： ant   fire regime   fire resilience   frequent fire   small mammal  

摘要： Tropical savannas are the world's most fire-prone biome, and savanna biotas are generally well adapted to frequent fire. However, in northern Australia there are concerns that recent increases in the frequency and extent of high-intensity fires are causing substantial declines in regional biodiversity values. In this paper we use two well-studied and contrasting faunal groups, ants and small mammals, as case studies for reviewing faunal responses to fire in Australian savannas. The Australian savanna ant fauna is dominated by arid-adapted taxa that are highly resilient to frequent fire and are not considered to be threatened by prevailing fire regimes. Indeed, frequent fire promotes ant diversity because it maintains an open habit that makes the dominant arid-adapted taxa feel at home. Long-term fire exclusion reduces ant diversity due to a marked decline in arid-adapted taxa, and favours highly generalized, more shade-tolerant taxa. In contrast, many small mammal species of high conservation value are highly sensitive to frequent fire, and there are widespread concerns that their populations are threatened by current fire management. Many of the species have shown dramatic population declines over recent decades, and, although the causes are poorly understood, there is little doubt that fire is an important contributing factor. It is likely that fire is acting synergistically with other underlying causes of decline, particularly predation by feral cats. The overall resilience of most savanna animal species in relation to frequent fire suggests that they are secure under all but the most extreme fire regimes. However, it is clear that more fire-sensitive groups such as small mammals need special fire management attention. This needs to involve less frequent and finer-scale burning, along with the protection of some large, infrequently burnt source areas.

关键词： Apodemus sylvaticus   Direct seeding   Direct sowing   Predator preference   Seed predation  

摘要： Direct seeding is potentially a cost-effective method for creating woodland and is particularly suited to establishing mixtures of species. Seed predation can cause poor establishment, and information on granivore preference for seed of different species is essential to evaluate relative risk and the need for control measures. We investigated consistencies in the preference of small mammals for removing seeds of 12 tree and shrub species at three sites in southern England using freely available seeds presented as single or mixed species plots. Seed preferences were modelled as preference for removal of seeds of a particular species in relation to others present in a given time period. Across-site comparison of seed preference ranks showed significant agreement, especially at each extreme of the ranks. Quercus robur and Fagus sylvatica were always ranked first or second, followed by Corylus avellana and Acer pseudoplatanus, while Crataegus monogyna and Fraxinus excelsior were ranked last;the relative position of middle ranking species varied between tests. Removal of seeds of highly preferred species was usually absolute, whereas seeds of lower ranked species were more likely to be partially removed. For most species, preference coefficients were positively related to two explanatory variates: the logarithms of whole seed and coat dry mass. The exception was Fraxinus excelsior, where preference was lower than predicted, possibly because of chemical defences. Presentation of seeds as either single or mixed species plots had no overall effect on preference ranking. The results suggest that species that produce large nuts, are more vulnerable to predation-loss and might require additional measures, such as treatment with repellents, to reduce predation risk, or might, as in the case of Q robur, be so attractive to rodents that it is unrealistic to direct sow them. The majority of the other species with smaller seed size, however, were much less susceptible to removal by

关键词： Brownian motion   character displacement   coexistence   competition   ecophylogenetics   environmental filtering   phylogenetic imbalance   Yotvata, Israel  

摘要： The distribution of traits within communities is thought to provide information on the evolutionary and ecological forces that structure community composition. Ecological character displacement (evolutionary divergence among populations of interacting species within a community), as well as community-wide character displacement (even dispersion of species traits within a community via species sorting), have been widely reported and are typically interpreted as evidence for interspecific competition. However, defining an appropriate null distribution with which to assess the observed distribution of traits within a community has proved controversial. Phylogenetic methods provide an alternative approach to evaluating community structure, but such methods also require an appropriate null and have typically overlooked the potential for evolutionary dynamics within communities. Here, we present a novel phylogenetic framework that uses evolutionary expectations to generate a simple null model of the expected distribution of traits among co-occurring species. Using a stochastic Brownian motion model of trait change, we illustrate that the expected community-wide dispersion of traits varies with phylogenetic tree shape. We then use data on body mass for mammals to evaluate the accuracy with which phylogeny can predict the empirical distribution of traits and find a strong correlation between predicted and observed trait distributions. We suggest that deviations from phylogenetic expectations may therefore provide a useful tool for evaluating the role of competition in shaping community structure. Finally, we demonstrate the utility of our approach using empirical data on body mass and a phylogeny for a small community of terrestrial mammals in Yotvata, Israel, and reveal evidence consistent with ecological and community-wide character displacement. Our method unites ecological and evolutionary approaches, and it provides a novel framework for exploring community structure.

关键词： agriculture   livestock   native pasture   nutrient enrichment   rotational grazing   woodland  

摘要： The relative effects of tree clearing, increased livestock densities and nutrient enrichment have rarely been compared across markedly different organism types, but negative effects are generally predicted. In contrast, adoption of rotational grazing is thought to benefit biodiversity in pastures but there are few supporting data. We examined the response of native plants, birds and reptiles to livestock management in south-eastern Australia. We selected 12 pairs of rotationally and continuously grazed farms. Two 1-ha plots were established in native pastures on each farm, one cleared and the second still retaining woodland tree cover. Stocking rates, fertilizer histories and landscape tree cover varied among farms. The abundance and richness of all taxa was lower in cleared pastures. The less mobile organisms (reptiles and plants) were positively correlated with tree cover at landscape scales, but only when trees were present at the plot scale. This pattern was driven by a few observations in landscapes with approximately 50% tree canopy cover. Neither bird abundance nor richness was correlated with stocking rates or nutrient enrichment, but plant richness responded negatively to both. The response of reptiles varied, declining with nutrient enrichment but positively correlated with livestock densities. These responses may be partly interpreted within the context of prior filtering of species pools through long-term grazing pressure. No taxa responded positively to rotational grazing management. We predict that reductions in livestock density and soil nutrients will directly benefit plants and less so reptiles, but not birds. Indirect benefits are predicted for birds and reptiles if management increases persistence of trees within paddocks. Although some forms of rotational grazing can increase woodland tree recruitment, rotational grazing in itself is unlikely to enhance diversity.

关键词： grazing   management   disturbance   kangaroo   Pseudomys  

摘要： The introduction of domestic cattle into systems that have had little historical grazing by large herbivores, such as the case in Australia, can lead to both direct and indirect changes in native flora and fauna. In this study, we investigate the differences in native mammal abundance between pastoral land managed for cattle production and conservation land in Australian tropical savannas. We systematically sampled 68 sites for mammals in north-eastern Queensland representing the two land tenures, which represent land with introduced stock and native herbivores present, and land where only native herbivores occur. We recorded 17 species of mammals representing five families and two functional groups (small mammals and macropods). Generalized linear mixed effects models identified that there was a significant positive relationship between increasing total ground cover and small mammal abundance and also the abundance of two species, Pseudomys desertor and P.?gracilicaudatus. We recorded a reduction in abundance on pastoral land for macropods and small mammals, and four species, M.?robustus, M.?rufus, Leggadina lakedownensis, P.?gracilicaudatus. Total ground cover and perennial grass cover was lower on pastoral land. Small mammal abundance on pastoral land was less even with increasing ground cover. Our results suggest that on pastoral land, native mammal abundance is affected and this has some relationship to ground cover changes. We recognize that there are other confounding management differences between pastoral and conservation lands such fire use, dingo baiting, and the manner of weed invasion and control that could influence mammal pattern. We conclude that conservation strategies for mammals in Australia's tropical savannas need to include a variety of land management schemes and tenures including land free from grazing by domestic livestock.

关键词： Density dependence   North-east India   Rodents   Seed predation   Seed dispersal  

摘要： Tropical tree species vary widely in their pattern of spatial dispersion. We focus on how seed predation may modify seed deposition patterns and affect the abundance and dispersion of adult trees in a tropical forest in India. Using plots across a range of seed densities, we examined whether seed predation levels by terrestrial rodents varied across six large-seeded, bird-dispersed tree species. Since inter-specific variation in density-dependent seed mortality may have downstream effects on recruitment and adult tree stages, we determined recruitment patterns close to and away from parent trees, along with adult tree abundance and dispersion patterns. Four species (Canarium resiniferum, Dysoxylum binectariferum, Horsfieldia kingii, and Prunus ceylanica) showed high predation levels (78.5-98.7%) and increased mortality with increasing seed density, while two species, Chisocheton cumingianus and Polyalthia simiarum, showed significantly lower seed predation levels and weak density-dependent mortality. The latter two species also had the highest recruitment near parent trees, with most abundant and aggregated adults. The four species that had high seed mortality had low recruitment under parent trees, were rare, and had more spaced adult tree dispersion. Biotic dispersal may be vital for species that suffer density-dependent mortality factors under parent trees. In tropical forests where large vertebrate seed dispersers but not seed predators are hunted, differences in seed vulnerability to rodent seed predation and density-dependent mortality can affect forest structure and composition.