57 research outputs found
Study of the multi-species annihilating random walk transition at zero branching rate - cluster scaling behavior in a spin model
Numerical and theoretical studies of a one-dimensional spin model with
locally broken spin symmetry are presented. The multi-species annihilating
random walk transition found at zero branching rate previously is investigated
now concerning the cluster behaviour of the underlying spins. Generic power law
behaviors are found, besides the phase transition point, also in the active
phase with fulfillment of the hyperscaling law. On the other hand scaling laws
connecting bulk- and cluster exponents are broken - a possibility in no
contradiction with basic scaling assumptions because of the missing absorbing
phase.Comment: 7 pages, 6 figures, final form to appear in PRE Nov.200
Generalized contact process on random environments
Spreading from a seed is studied by Monte Carlo simulation on a square
lattice with two types of sites affecting the rates of birth and death. These
systems exhibit a critical transition between survival and extinction. For
time- dependent background, this transition is equivalent to those found in
homogeneous systems (i.e. to directed percolation). For frozen backgrounds, the
appearance of Griffiths phase prevents the accurate analysis of this
transition. For long times in the subcritical region, spreading remains
localized in compact (rather than ramified) patches, and the average number of
occupied sites increases logarithmically in the surviving trials.Comment: 6 pages, 7 figure
Dead or alive? Comparing costs and benefits of lethal and non-lethal human-wildlife conflict mitigation on livestock farms
Livestock depredation has implications for conservation
and agronomy; it can be costly for farmers and
can prompt retaliatory killing of carnivores. Lethal control
measures are readily available and are reportedly perceived
to be cheaper, more practical and more effective than nonlethal
methods. However, the costs and efficacy of lethal vs
non-lethal approaches have rarely been compared formally.
We conducted a 3-year study on 11 South African livestock
farms, examining costs and benefits of lethal and non-lethal
conflict mitigation methods. Farmers used existing lethal
control in the first year and switched to guardian animals
(dogs Canis familiaris and alpacas Lama pacos) or livestock
protection collars for the following 2 years. During the first
year the mean cost of livestock protection was USD 3.30 per
head of stock and the mean cost of depredation was
USD 20.11 per head of stock. In the first year of non-lethal
control the combined implementation and running costs
were similar to those of lethal control (USD 3.08 per head).
However, the mean cost of depredation decreased by 69.3%,
to USD 6.52 per head. In the second year of non-lethal
control the running costs (USD 0.43 per head) were significantly
lower than in previous years and depredation
costs decreased further, to USD 5.49 per head. Our results
suggest that non-lethal methods of human–wildlife conflict
mitigation can reduce depredation and can be economically
advantageous compared to lethal methods of predator
control.ABAX Foundation (previously the Polaris Foundation), Pick'n Pay, Woolworths, the Henry and Iris Englund Foundation, the National Lotteries Distribution Trust Fund, Arne Hanson, the Mones Michaels Trust and Royal Canin. Wits–Carnegie fellowship and Kaplan Senior Research Fellow at Pembroke College. Recanati–Kaplan Foundation,
the Peoples' Trust for Endangered Species and the Swift family.http://journals.cambridge.org/action/displayJournal?jid=ORXhb2016Mammal Research Institut
Slow relaxation in weakly open vertex-splitting rational polygons
The problem of splitting effects by vertex angles is discussed for
nonintegrable rational polygonal billiards. A statistical analysis of the decay
dynamics in weakly open polygons is given through the orbit survival
probability. Two distinct channels for the late-time relaxation of type
1/t^delta are established. The primary channel, associated with the universal
relaxation of ''regular'' orbits, with delta = 1, is common for both the closed
and open, chaotic and nonchaotic billiards. The secondary relaxation channel,
with delta > 1, is originated from ''irregular'' orbits and is due to the
rationality of vertices.Comment: Key words: Dynamics of systems of particles, control of chaos,
channels of relaxation. 21 pages, 4 figure
Solution of voter model dynamics on annealed small-world networks
An analytical study of the behavior of the voter model on the small-world
topology is performed. In order to solve the equations for the dynamics, we
consider an annealed version of the Watts-Strogatz (WS) network, where
long-range connections are randomly chosen at each time step. The resulting
dynamics is as rich as on the original WS network. A temporal scale
separates a quasi-stationary disordered state with coexisting domains from a
fully ordered frozen configuration. is proportional to the number of
nodes in the network, so that the system remains asymptotically disordered in
the thermodynamic limit.Comment: 11 pages, 4 figures, published version. Added section with extension
to generic number of nearest neighbor
Conservation inequality and the charismatic cat: Felis felicis
AbstractConservation resources are limited, making it impossible to invest equally in all threatened species. One way to maximise conservation gains is to focus upon those species with particular public appeal, using them to generate funding and support that could also benefit less charismatic species. Although this approach is already used by many conservation organisations, no reliable metrics currently exist to determine the likely charisma of a given species, and therefore identify the most appropriate targets for such campaigns. Here we use market research techniques on over 1500 people from five continents to assess the relative charisma of different mammals, which factors appear to drive it, and how these patterns vary between countries. Felids and primates emerged as highly favoured species for conservation, with the tiger (Panthera tigris) the top species by a wide margin. Using an information theoretic approach we develop models that successfully predict respondents’ preferences across the entire sample, suggesting global commonalities in the attributes that people prefer for conservation. However, by analysing each country separately we are able to improve our models, thus highlighting the importance of identifying locally specific flagships for conservation. The most important attributes were body size and IUCN status, although the extent of baldness, whether the species was a potential threat to humans and whether the eyes were forward or side facing were also widely important. Several of the key attributes revealed in this study could be extrapolated to nearly all terrestrial mammals, paving the way for a standardised global identification of species likely to prove effective for future conservation campaigns. The public preferred species with which they had affinity and familiarity, and we discuss how these aspects could be increased to promote the under-achievers, whilst maximising the funding potential of the highly charismatic mammals. While the felids are widely regarded as a popular taxonomic group, the great extent to which they appealed to our respondents emphasises their potential as ambassadors for conservation. Indeed, the big cats were so highly rated that we might think of them as one, Felis felicis: a globally powerful flagship for conservation
The relative effects of prey availability, anthropogenic pressure and environmental variables on lion (Panthera leo) site use in Tanzania's Ruaha landscape during the dry season
African lion (Panthera leo) populations have been reduced by almost half in the past two decades, with national parks and game reserves maintaining vital source populations, particularly in East Africa. However, much of the habitats necessary to support lion populations occur in unprotected lands surrounding protected areas. There is an ongoing need for understanding the ecological determinants of lion occurrence in these unprotected habitats, where lions are most vulnerable to extinction. This study evaluated variations in lion site use along a gradient of anthropogenic pressure encompassing the Ruaha National Park, Pawaga‐Idodi Wildlife Management Area (WMA) and unprotected village lands via camera‐trapping. We collected lion occurrence data in the dry seasons of 2014 and 2015, and modelled lion site use as a function of environmental and anthropogenic variables under a Bayesian framework. We recorded 143 lion detections within the national park, 14 in the WMA and no detections in village lands. This result does not imply that lions never use the village lands, but rather that we did not detect them in our surveys during the dry season. Our findings suggest that lion site use was primarily associated with high seasonal wild prey biomass in protected areas. Thus, we infer that human‐induced prey depletion and lion mortality are compromising lion site use of village lands. Seasonal prey movements, and a corresponding concentration inside the park during sampling, could also play an important role in lion site use. These findings reinforce the need to secure large‐bodied prey base to conserve lions, and the importance of protected areas as key refugia for the species
Absorbing-state phase transitions in fixed-energy sandpiles
We study sandpile models as closed systems, with conserved energy density
playing the role of an external parameter. The critical energy density,
, marks a nonequilibrium phase transition between active and absorbing
states. Several fixed-energy sandpiles are studied in extensive simulations of
stationary and transient properties, as well as the dynamics of roughening in
an interface-height representation. Our primary goal is to identify the
universality classes of such models, in hopes of assessing the validity of two
recently proposed approaches to sandpiles: a phenomenological continuum
Langevin description with absorbing states, and a mapping to driven interface
dynamics in random media. Our results strongly suggest that there are at least
three distinct universality classes for sandpiles.Comment: 41 pages, 23 figure
Phase transition and selection in a four-species cyclic Lotka-Volterra model
We study a four species ecological system with cyclic dominance whose
individuals are distributed on a square lattice. Randomly chosen individuals
migrate to one of the neighboring sites if it is empty or invade this site if
occupied by their prey. The cyclic dominance maintains the coexistence of all
the four species if the concentration of vacant sites is lower than a threshold
value. Above the treshold, a symmetry breaking ordering occurs via growing
domains containing only two neutral species inside. These two neutral species
can protect each other from the external invaders (predators) and extend their
common territory. According to our Monte Carlo simulations the observed phase
transition is equivalent to those found in spreading models with two equivalent
absorbing states although the present model has continuous sets of absorbing
states with different portions of the two neutral species. The selection
mechanism yielding symmetric phases is related to the domain growth process
whith wide boundaries where the four species coexist.Comment: 4 pages, 5 figure
Novel universality class of absorbing transitions with continuously varying critical exponents
The well-established universality classes of absorbing critical phenomena are
directed percolation (DP) and directed Ising (DI) classes. Recently, the pair
contact process with diffusion (PCPD) has been investigated extensively and
claimed to exhibit a new type of critical phenomena distinct from both DP and
DI classes. Noticing that the PCPD possesses a long-term memory effect, we
introduce a generalized version of the PCPD (GPCPD) with a parameter
controlling the memory effect. The GPCPD connects the DP fixed point to the
PCPD point continuously. Monte Carlo simulations show that the GPCPD displays
novel type critical phenomena which are characterized by continuously varying
critical exponents. The same critical behaviors are also observed in models
where two species of particles are coupled cyclically. We suggest that the
long-term memory may serve as a marginal perturbation to the ordinary DP fixed
point.Comment: 13 pages + 10 figures (Full paper version
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