20 research outputs found
Diffusion and Home Range Parameters for Rodents: Peromyscus maniculatus in New Mexico
We analyze data from a long term field project in New Mexico, consisting of
repeated sessions of mark-recaptures of Peromyscus maniculatus (Rodentia:
Muridae), the host and reservoir of Sin Nombre Virus (Bunyaviridae:
Hantavirus). The displacements of the recaptured animals provide a means to
study their movement from a statistical point of view. We extract two
parameters from the data with the help of a simple model: the diffusion
constant of the rodents, and the size of their home range. The short time
behavior shows the motion to be approximately diffusive and the diffusion
constant to be 470+/-50m^2/day. The long time behavior provides an estimation
of the diameter of the rodent home ranges, with an average value of 100+/-25m.
As in previous investigations directed at Zygodontomys brevicauda observations
in Panama, we use a box model for home range estimation. We also use a harmonic
model in the present investigation to study the sensitivity of the conclusions
to the model used and find that both models lead to similar estimates.Comment: The published paper in Ecol. Complexity has an old version of Figure
6. Here we have put the correct version of Figure
Controls of forage selective defoliation by sheep in arid rangelands
Selective grazing by domestic livestock is a major control of plant community structure anddynamics in drylands. However, grazing impact predictions supporting management decisions are fre-quently based on average biomass consumption, neglecting selectivity. We evaluated the relative impor-tance of grazing pressure, total and each species density, and plant dead biomass proportion as drivers ofselective defoliation by sheep in three dominant native grass species in Patagonian steppes. Species werePoa ligularis,Festuca pallescens,andPappostipa speciosa, whicha prioripresent different preference degree bysheep. The relevance of these drivers for differently preferred species has not been simultaneously studied.We recorded the defoliation frequency and degree of the three species (dependent variables) throughout112field surveys. Besides, we recorded grazing management and vegetation structure descriptors (inde-pendent variables).Poa ligulariswas highly defoliated (90% of plants), and grazing pressure was the lead-ing driver (asymptotic exponential relationship). ForF. pallescens, almost 70% of plants were defoliated,and defoliation non-linearly increased as grazing pressure rose and linearly decreased as both its dead bio-mass proportion andP. ligularisdensity increased. ForP. speciosa, defoliation was low (20% of plants) andlinearly decreased as both its dead biomass proportion and the density of the other two species increased.Grazing pressure played a negligible role in this species. These patterns confirmed thatP. ligularis,F. palles-cens,andP. speciosa,respectively, present high, intermediate, and low preference degree by sheep. In con-clusion, ourfindings suggest that (1) selective defoliation can be satisfactorily predicted as function ofgrazing pressure, species densities, and plant dead biomass proportion; (2) grazing pressure becomes amore relevant driver as species preference rises and its effect on defoliation is markedly non-linear; (3) thedead biomass proportion and the abundance of highly preferred species are the leading factors determin-ing less preferred species defoliation; and (4) grazing pressure management by itself is not enough toreduce the high defoliation of preferred species and increase the defoliation of non-preferred species. Thisknowledge is critical for developing effective management practices to control forage species defoliation inrangelands worldwide where species with different preference by herbivores coexist
A Theoretical Framework for the Analysis of the West Nile Virus Epidemic
We present a model for the growth of West Nile virus in mosquito and bird
populations based on observations of the initial epidemic in the U.S. Increase
of bird mortality as a result of infection, which is a feature of the epidemic,
is found to yield an effect which is observable in principle, viz., periodic
variations in the extent of infection. The vast difference between mosquito and
bird lifespans, another peculiarity of the system, is shown to lead to
interesting consequences regarding delay in the onset of the steady-state
infection. An outline of a framework is provided to treat mosquito diffusion
and bird migration.Comment: 12 pages, 9 postscript figure
Diversity and Community Similarity of Arthropods in Response to the Restoration of Former Pine Plantations
Abstract Ecological restoration is becoming an increasingly important tool in humanity\u27s attempt to manage, conserve, and repair the world\u27s ecosystems. In the current study, the objective was to compare the effects of two restoration methods on arthropod biodiversity and community composition in two former pine plantations; these treatments included both intensive restoration effort (= cleared) and moderate restoration effort (= thinned). For the cleared treatment, vegetation was clear-cut to the soil surface, and all vegetation was removed from the plots, while the thinned treatment consisted of reducing the Pinus elliotii (Slash Pine) density to that of a native ecosystem and removing of all exotic plants from the plots as well. Arthropods were sampled by employing pitfall traps, sticky traps, and sweep netting and identified to family and morphospecies; species richness, diversity, and community similarity were compared between treatments and sites. Experimental treatments quickly reached or exceeded arthropod diversity and richness of an unmanipulated control treatment; however, the two sites produced non-overlapping ordination plots, suggesting that the diversity of the two sites are either compositionally different (alpha diversity) or community assemblage is incomplete and overall regional (beta) diversity has not reached an equilibrium across sites. Additional long-term data should reveal if these plots are proceeding along different successional trajectories in terms of community species composition, or whether treatments, while having similar richness, support different communities because the three types of plots used in this study (control, thinned, and cleared) represent various successional stages which affect arthropod species identity, but not overall richness