Home About us Contact
|
Home About us Contact | ||
|
|
||
Heterogeneous Habitat (heterogeneous + habitat)
Selected AbstractsMovement trajectories and habitat partitioning of small mammals in logged and unlogged rain forests on BorneoJOURNAL OF ANIMAL ECOLOGY, Issue 5 2006KONSTANS WELLS Summary 1Non-volant animals in tropical rain forests differ in their ability to exploit the habitat above the forest floor and also in their response to habitat variability. It is predicted that specific movement trajectories are determined both by intrinsic factors such as ecological specialization, morphology and body size and by structural features of the surrounding habitat such as undergrowth and availability of supportive structures. 2We applied spool-and-line tracking in order to describe movement trajectories and habitat segregation of eight species of small mammals from an assemblage of Muridae, Tupaiidae and Sciuridae in the rain forest of Borneo where we followed a total of 13 525 m path. We also analysed specific changes in the movement patterns of the small mammals in relation to habitat stratification between logged and unlogged forests. Variables related to climbing activity of the tracked species as well as the supportive structures of the vegetation and undergrowth density were measured along their tracks. 3Movement patterns of the small mammals differed significantly between species. Most similarities were found in congeneric species that converged strongly in body size and morphology. All species were affected in their movement patterns by the altered forest structure in logged forests with most differences found in Leopoldamys sabanus. However, the large proportions of short step lengths found in all species for both forest types and similar path tortuosity suggest that the main movement strategies of the small mammals were not influenced by logging but comprised generally a response to the heterogeneous habitat as opposed to random movement strategies predicted for homogeneous environments. 4Overall shifts in microhabitat use showed no coherent trend among species. Multivariate (principal component) analysis revealed contrasting trends for convergent species, in particular for Maxomys rajah and M. surifer as well as for Tupaia longipes and T. tana, suggesting that each species was uniquely affected in its movement trajectories by a multiple set of environmental and intrinsic features. [source] Exploration correlates with settlement: red squirrel dispersal in contrasting habitatsJOURNAL OF ANIMAL ECOLOGY, Issue 6 2004DIANE L. HAUGHLAND Summary 1Dispersers in heterogeneous habitat theoretically should target the habitat(s) where reproduction and survival (i.e. fitness) will be highest. However, the cues that dispersing animals respond to are not well understood: differences in habitat quality ultimately may be important, but whether animals respond to these differences may be influenced by their own familiarity with different habitats. 2To determine if dispersers reacted to differences in habitat, we documented the exploratory movements, dispersal, and settlement patterns of juvenile North American red squirrels (Tamiasciurus hudsonicus) originating in adjacent patches of different habitats. 3Dispersers originating in mature, closed-canopy forest (linked to higher female reproductive success and smaller territories) did not explore contrasting open forest with lower tree densities, and the magnitude of the dispersers' explorations was relatively similar. In contrast, dispersers from the open forest habitat made explorations that carried them into contrasting, mature forest habitat, and their explorations were more variable across individuals. 4When settlement occurred, it was strongly philopatric in all groups of dispersers, although the distances and directions favoured during the exploratory phase of dispersal remained strong predictors of where settlement occurred. Overall, processes favouring philopatry (i.e. maternal influences, competitive advantages, etc.) appeared to dominate the dispersal of our study animals, even those that were exposed to higher quality habitat during their explorations. 5Secondarily, annual stochasticity (or some correlate) affected the scale of exploration and timing of settlement more than the relative quality of habitat in which dispersers were born. 6Studies such as this that seek to understand the relative importance of individual experience, habitat familiarity, and habitat quality are important to ultimately understanding how individual animals and populations react to habitat heterogeneity. [source] Species diversity and population dynamics of rodents in a farm-fallow field mosaic system in Central TanzaniaAFRICAN JOURNAL OF ECOLOGY, Issue 2 2010Rhodes H. Makundi Abstract A Capture-Mark-Recapture study was undertaken in Central Tanzania to compare variations in community structure and population dynamics of rodents in two types of habitats. The study was conducted in fallow field mosaic habitat dominated by perennial and annual grasses (grid BEA) and a more heterogeneous habitat (grid BEB) which was previously woodland cleared of most trees with vegetation dominated by shrubs, bushes, scattered trees and perennial grass. The relative abundance of rodents in BEA was: Mastomys natalensis (73.5%) > Aethomys chrysophilus (8.9%) > Gerbilliscus vicina (7.3%) > Arvicanthis neumanni (6.1%) > Acomys spinosissimus (4.1%) and for grid BEB: M. natalensis (67.6%) > G. vicina (11.2%) > A. neumanni (10.3%) > A. chrysophilus (7.6%) > A. spinosissimus (2.9%). Graphiurus sp., Mus minutoides, Saccostomus mearnsi, Lemniscomys striatus and L. griselda were rare and only occasionally trapped in BEB. Spatial variations in population density were non-significant except for A. chrysophilus. Significant temporal variations within grids were observed, with synchrony of population peaks for some species. The rare species boosted species richness of grid BEB rather artificially, without significantly contributing to higher species diversity. Temporal variations in Simpson's Diversity indices between grids were non-significant except for three out of twenty-one trapping sessions. Résumé Une étude par capture , marquage , recapture fut entreprise dans le centre de la Tanzanie pour comparer les variations de la structure des communautés et de la dynamiques des populations de rongeurs dans deux types d'habitats. L'étude fut menée dans un habitat composé d'une mosaïque de prairies en jachères dominé par des herbes pérennes et annuelles (grille BEA) et dans un habitat plus hétérogène (grille BEB) qui était auparavant une forêt, défrichée de la plupart de ses arbres et dominée par des buissons, des arbustes, des arbres épars et des herbes pérennes. L'abondance relative des rongeurs dans BEA était la suivante : Mastomys natalensis (73,5%) > Aethomys chrysophilus (8,9%) > Gerbilliscus vicina (7,3%) > Arvicanthis neumanni (6,1%) > Acomys spinosissimus (4,1%), et pour la grille BEB: M natalensis (67,6%) > G. vicina (11,2%) > A. neumanni (10,3%) > A. chrysophilus (7,6%) > A. spinosissimus (2,9%). Graphiurus sp. Mus minutoides, Saccostomus mearnsi, Lemniscomys striatus et L. griseldaétaient rares et n'étaient que rarement capturés dans BEB. Les variations spatiales de la densité de population n'étaient pas significatives sauf pour A. chrysophilus. Des variations temporelles significatives furent observées à l'intérieur des grilles, ainsi qu'une synchronisation des pics de population pour certaines espèces. Les espèces rares renforçaient de façon plutôt artificielle la richesse en espèces de la grille BEB, sans contribuer significativement à une plus grande diversité des espèces. Des variations temporelles des indices de diversité de Simpson entre les grilles n'étaient pas significatives sauf pour trois des 21 sessions de captures. [source] Extension of ideal free resource use to breeding populations and metapopulationsOIKOS, Issue 1 2000C. Patrick Doncaster The concept of an ideal and free use of limiting resources is commonly invoked in behavioural ecology as a null model for predicting the distribution of foraging consumers across heterogeneous habitat. In its original conception, however, its predictions were applied to the longer timescales of habitat selection by breeding birds. Here I present a general model of ideal free resource use, which encompasses classical deterministic models for the dynamics in continuous time of feeding aggregations, breeding populations and metapopulations. I illustrate its key predictions using the consumer functional response given by Holling's disc equation. The predictions are all consistent with classical population dynamics, but at least two of them are not usually recognised as pertaining across all scales. At the fine scale of feeding aggregations, the steady state of an equal intake for all ideal free consumers may be intrinsically unstable, if patches are efficiently exploited by individuals with a non-negligible handling time of resources. At coarser scales, classical models of population and metapopulation dynamics assume exploitation of a homogeneous environment, yet they can yield testable predictions for heterogeneous environments too under the assumption of ideal free resource use. [source] IS INBREEDING DEPRESSION LOWER IN MALADAPTED POPULATIONS?EVOLUTION, Issue 7 2009A QUANTITATIVE GENETICS MODEL Despite abundant empirical evidence that inbreeding depression varies with both the environment and the genotypic context, theoretical predictions about such effects are still rare. Using a quantitative genetics model, we predict amounts of inbreeding depression for fitness emerging from Gaussian stabilizing selection on some phenotypic trait, on which, for simplicity, genetic effects are strictly additive. Given the strength of stabilizing selection, inbreeding depression then varies simply with the genetic variance for the trait under selection and the distance between the mean breeding value and the optimal phenotype. This allows us to relate the expected inbreeding depression to the degree of maladaptation of the population to its environment. We confront analytical predictions with simulations, in well-adapted populations at equilibrium, as well as in maladapted populations undergoing either a transient environmental shift, or gene swamping in heterogeneous habitats. We predict minimal inbreeding depression in situations of extreme maladaptation. Our model provides a new basis for interpreting experiments that measure inbreeding depression for the same set of genotypes in different environments, by demonstrating that the history of adaptation, in addition to environmental harshness per se, may account for differences in inbreeding depression. [source] Distribution and ecophysiology of the nitrifying bacteria emphasizing cultured speciesFEMS MICROBIOLOGY ECOLOGY, Issue 1 2001Hans-Peter Koops Abstract Nitrification is an important factor in the global nitrogen cycle. Therefore, an increasing number of publications deal with in situ studies of natural bacterial populations participating in this process. However, some crucial points complicate suchlike investigations. At the time being, a total of 25 species of ammonia-oxidizers and eight species of nitrite-oxidizers are cultured but the existence of many more species has been indicated by molecular in situ investigations. With that, only a part of the existing nitrifiers has been defined via isolation and subsequent physiological and molecular characterization. Furthermore, the distribution patterns of the distinct species of nitrifiers depend on various environmental parameters. Hence the composition of nitrifying bacterial communities is complex and divers in heterogeneous habitats. In consequence of the above-mentioned problems, the representation of nitrifying community structures obtained from in situ investigations often has been incomplete and unbalanced in many respects. Polyphasic approaches, applying a combination of classical as well as molecular methods in parallel, could help to find the way for overcoming these problems in the future. Isolation and characterization of as many as possible new species seems to be one of the most important missing steps to advance at this way. [source] Modelling the establishment and spread of autotetraploid plants in a spatially heterogeneous environmentJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2004B.-H. Li Abstract The establishment and spread of autotetraploids from an original diploid population in a heterogeneous environment were studied using a stochastic simulation model. Specifically, we investigated the effects of heterogeneous habitats and nonrandom pollen/seed dispersal on the critical value (,) of unreduced 2n gamete production necessary for the establishment of autotetraploids as predicted by deterministic models. Introduction of a heterogeneous environment with random pollen/seed dispersal had little effect on the , value. In contrast, incorporating nonrandom pollen/seed dispersal into a homogeneous environment considerably reduced the , value. Incorporating both heterogeneous habitats and nonrandom pollen/seed dispersal may lead either to an increase or to a decrease in the , value compared to that with random dispersal, indicating that the two factors interact in a complex way. [source] | ||||||||||