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Rolf A. Ims - One of the best experts on this subject based on the ideXlab platform.
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THE EFFECT OF Habitat CorridorS ON RATES OF TRANSFER AND INTERBREEDING BETWEEN VOLE DEMES
Ecology, 1999Co-Authors: Jon Aars, Rolf A. ImsAbstract:It has been proposed that Habitat Corridors enhance exchange of individuals (transfer) and interbreeding between otherwise isolated demes in fragmented populations. However, due to the paucity of experimental studies this proposition has become contro- versial. We tested these proposed effects of Corridors in 12 experimentally fragmented root vole populations. A 50-m long Habitat Corridor connected two large Habitat patches in each of six treatment populations, while equivalent Habitat patches in six control populations had no Corridor connection. Each of the two patches in each population was initially colonized by founder demes that were monomorphic with respect to two different marker alleles of a single locus. The rate of transfer of individuals and the resultant degree of interbreeding (heterozygosity) between the two demes were monitored by capture-recapture methodology and genetic analyses over the reproductive season. Females were predominantly philopatric in these populations; more than four-fifths of the founder deme females settled and reproduced in their original patch. However, Corridors significantly facilitated the transfer of females. The transfer rate of males was generally very high; approximately four-fifths, independent of the experimental factor (absence or presence of Corridors). The sex-specific transfer pattern gave rise to very high rates of interbreeding (heterozygosity). The rate of interbreeding was enhanced by the presence of Corridors, and more so than expected from the transfer rate. The lack of concordance between expected and observed heterozygosity in the Corridor populations was probably due to short-term mating excursions facilitated by the presence of Corridors.
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Demographic consequences of movements in subdivided root vole populations
Oikos, 1999Co-Authors: Jon Aars, Edda Johannesen, Rolf A. ImsAbstract:We studied three types of movements: (1) movements leading to permanent transfer of individuals between Habitat patches, (2) movements (excursions) into Habitat Corridors and (3) into a barren matrix area, and the demographic consequences in 12 enclosed populations of the root vole, Micrototus oeconomus. Each population was subdivided into two demes inhabiting one Habitat patch each. The two patches were approximately two male home range diameters apart in a vole-hostile, devegetated matrix. While the patches were connected by a narrow (0.5 m) Habitat Corridor for six of the populations, the other six populations inhabited isolated patches. The experiment was initiated by introducing laboratory raised founder demes onto each patch in the beginning of July. The populations were thereafter monitored by live trapping for the next 4-5 months during the snow-free season. After the snow melted the following spring the experiment was terminated by removal trapping. The experiment was run over two years (1994 and 1995) with six population replicates each year. Movements into the Corridors and permanent transfers of animals between patches were registered during ordinary live trapping at 15-d intervals. Movements into the barren matrix Habitat were registered continuously during the snow-free season by activating edge traps along the fences of the enclosures every night. Except for males early in the summer, movements leading to transfer of individuals between demes were rare relative to mortality and recruitment, and transfer did not act to synchronize the dynamics between demes. Moreover, transferred animals possessed the same survival probability as those staying in their natal deme. Corridors slightly enhanced the rate of transfer in females, but not in males. Excursions into Corridors and the matrix area took place much more frequently than transfer and most frequently in the first cohorts early in the season and more in males than in females. Movements in the hostile matrix had a considerable negative effect on survival and, thus on the demography of the populations. Predation by birds is the most likely cause of this movement related mortality which may play an important role in the dynamics of patchy vole populations during the snow-free season. Movements into the Corridors did not have any independent effect on survival probability, and Habitat Corridors may thus act to transfer animals more safely from one patch to another.
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Discontinuous Habitat Corridors : effects on male root vole movements
The Journal of Applied Ecology, 1996Co-Authors: Harry P. Andreassen, Rolf A. Ims, Ole Knut SteinsetAbstract:We tested how movement rates of male root voles were affected by discontinuities (gaps) in a 1-m wide Habitat Corridor. Gaps of increasing size (0.25-4m) were created experimentally by mowing the vegetation. Movement rates (recorded by radiotelemetry) were compared between the manipulated Corridor and a contemporal, unmanipulated (continuous) control Corridor. Male root voles did not respond to gaps until the gap size became 4m which is equivalent to 10-20% of the normal home range diameter. Gap sizes of 4 m in the Corridor decreased the movement rates significantly and to the same degree for two behaviourally distinct strains of root voles. The similar responses of the two vole strains indicated that the results may have validity beyond the particular experimental setting employed.
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Optimal width of movement Corridors for root voles : not too marrow and not too wide
The Journal of Applied Ecology, 1996Co-Authors: Harry P. Andreassen, Stefan Halle, Rolf A. ImsAbstract:1. The characteristics of male root vole movements as a function of Corridor width were tested in a 310 m long Habitat Corridor connecting two Habitat patches. Detailed observations of movements were made by means of radiotelemetry and recording of footprints. 2. The highest connectivity, in terms of transference rate of individuals in the Corridor system, was observed in the intermediate of three Corridor widths tested (3 m, 1 m and 0.4 m). 3. The behavioural mechanism behind the lower connectivity of the narrowest Corridor was a reluctance of voles to enter it, while linear progress in the widest Corridor was hampered by a high frequency of cross-directional movements. 4. The relationship between Corridor width and movement behaviour was unaffected by the simulated presence of competitors and predators. 5. Our results challenge the 'the-wider-the-better' principle of movement Corridor design, and provide elements for an understanding of the behavioural mechanisms underlying the movement ecology of individuals in linear Habitats.
William B. Sherwin - One of the best experts on this subject based on the ideXlab platform.
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Induced dispersal in wildlife management: experimental evaluation of the risk of hybrid breakdown and the benefit of hybrid vigor in the F1 generation
Conservation Genetics, 2009Co-Authors: Clare E. Holleley, Richard A. Nichols, Michael R. Whitehead, Melissa R. Gunn, Jyoutsna Gupta, William B. SherwinAbstract:Management practices often aim to increase the level of gene flow by either: introducing animals from captive breeding programs, translocating animals from abundant areas, or increasing the chance of animals dispersing between populations by creating Habitat Corridors. These practices provide opportunity for the hybrid offspring of introduced and resident animals to experience either increased fitness (hybrid vigor) or decreased fitness (hybrid breakdown). There is very little quantitative data available to adequately assess whether hybridization is likely to be beneficial or detrimental to populations managed in these ways. Using Drosophila melanogaster populations, we conducted two experiments that simulate the common management practices of translocation and wildlife Habitat Corridors. We monitored the frequency and magnitude of hybrid vigor and hybrid breakdown in F1 hybrids to assess the relative risks and benefits to populations and also monitored net productivity (number of adults produced from controlled crosses) to assess whether the populations were stable or in decline. In the translocation experiment, we observed instances of both significant hybrid vigor and hybrid breakdown, both occurring at a frequency of 9%. In the Habitat Corridor experiments, populations with moderate to high dispersal (1–4% per generation) did not develop significant hybrid vigor or hybrid breakdown. However, of the populations experiencing low dispersal (0.25% per generation) for 34 generations, 6% displayed significant hybrid vigor and 6% displayed significant hybrid breakdown. These results suggest that in first generation hybrids there may be limited opportunity to utilize hybrid vigor as a tool to increase the short-term viability of populations because there is an equal likelihood of encountering hybrid breakdown that may drive the population into further decline. However, our results apply only to populations of moderate size (N = 50; Ne = 14.3) in the absence of deliberate consanguineous mating. Lastly, we observed that net productivity was positively correlated with dispersal rate, suggesting that initial F1 declines in fitness may be temporary and that it is preferable to maintain high levels of selectable variation via induced dispersal to assist the long-term survival of vulnerable populations.
Timothy M Eppley - One of the best experts on this subject based on the ideXlab platform.
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the use of an invasive species Habitat by a small folivorous primate implications for lemur conservation in madagascar
PLOS ONE, 2015Co-Authors: Laza Andriamandimbiarisoa, Jeanbaptiste Ramanamanjato, Faly Randriatafika, Giuseppe Donati, Timothy M Eppley, David Rabehevitra, Robertin Ravelomanantsoa, Jorg U GanzhornAbstract:The lemurs of Madagascar are among the most threatened mammalian taxa in the world, with Habitat loss due to shifting cultivation and timber harvest heavily contributing to their precarious state. Deforestation often leads to fragmentation, resulting in mixed-Habitat matrices throughout a landscape where disturbed areas are prone to invasion by exotic plants. Our study site, the Mandena littoral forest (southeast Madagascar), is a matrix of littoral forest, littoral swamp, and Melaleuca swamp Habitats. Here, Melaleuca quinquenervia has invaded the wetland ecosystem, creating a mono-dominant Habitat that currently provides the only potential Habitat Corridor between forest fragments. We sought to understand the role of this invasive Melaleuca swamp on the behavioral ecology of a threatened, small-bodied folivore, the southern bamboo lemur (Hapalemur meridionalis). We collected botanical and behavioral data on four groups of H. meridionalis between January and December 2013. Our results confirm Melaleuca swamp as an important part of their home range: while lemurs seasonally limited activities to certain Habitats, all groups were capable of utilizing this invasive Habitat for feeding and resting. Furthermore, the fact that Hapalemur use an invasive plant species as a dispersal Corridor increases our knowledge of their ecological flexibility, and may be useful in the conservation management of remaining threatened populations.
Christian Kerbiriou - One of the best experts on this subject based on the ideXlab platform.
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Road network in an agrarian landscape: Potential Habitat, Corridor or barrier for small mammals?
Acta Oecologica, 2015Co-Authors: Louis De Redon, Isabelle Le Viol, Frédéric Jiguet, Nathalie Machon, Olivier Scher, Christian KerbiriouAbstract:Abstract If the negative effects of road networks on biodiversity are now recognized, their role as barriers, Habitats or Corridors remain to be clarified in human altered landscapes in which road verges often constitute the few semi-natural Habitats where a part of biodiversity important for ecosystem functioning may maintain. In human-dominated landscape, their roles are crucial to precise in comparison to other Habitats for small mammal species considered as major natural actors (pests (voles) or biological control agents (shrew)). We studied these roles through the comparison of small mammal abundance captured (418 individuals belonging to 8 species) using non-attractive pitfall traps ( n = 813) in 176 sampled sites distributed in marginal zones of road and crop, in natural areas and in fields. We examined the effect of roadside width and isolation of sites. We found the higher small mammal abundances in roadside verges and an effect of width margins for shrews. The significant effect of the distance to the next adjacent natural Habitat at the same side of the road on the relative abundance of Sorex coronatus , and the absence of a significant effect of distance to the next natural Habitat at the opposite side of road, suggest that highway and road verges could be used as Corridor for their dispersal, but have also a barrier effect for shrews. Our results show that in intensive agricultural landscapes roadside and highway verges may often serve as refuge, Habitat and Corridor for small mammals depending on species and margin characteristics.
Jorg U Ganzhorn - One of the best experts on this subject based on the ideXlab platform.
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the use of an invasive species Habitat by a small folivorous primate implications for lemur conservation in madagascar
PLOS ONE, 2015Co-Authors: Laza Andriamandimbiarisoa, Jeanbaptiste Ramanamanjato, Faly Randriatafika, Giuseppe Donati, Timothy M Eppley, David Rabehevitra, Robertin Ravelomanantsoa, Jorg U GanzhornAbstract:The lemurs of Madagascar are among the most threatened mammalian taxa in the world, with Habitat loss due to shifting cultivation and timber harvest heavily contributing to their precarious state. Deforestation often leads to fragmentation, resulting in mixed-Habitat matrices throughout a landscape where disturbed areas are prone to invasion by exotic plants. Our study site, the Mandena littoral forest (southeast Madagascar), is a matrix of littoral forest, littoral swamp, and Melaleuca swamp Habitats. Here, Melaleuca quinquenervia has invaded the wetland ecosystem, creating a mono-dominant Habitat that currently provides the only potential Habitat Corridor between forest fragments. We sought to understand the role of this invasive Melaleuca swamp on the behavioral ecology of a threatened, small-bodied folivore, the southern bamboo lemur (Hapalemur meridionalis). We collected botanical and behavioral data on four groups of H. meridionalis between January and December 2013. Our results confirm Melaleuca swamp as an important part of their home range: while lemurs seasonally limited activities to certain Habitats, all groups were capable of utilizing this invasive Habitat for feeding and resting. Furthermore, the fact that Hapalemur use an invasive plant species as a dispersal Corridor increases our knowledge of their ecological flexibility, and may be useful in the conservation management of remaining threatened populations.
