INVESTIGADORES
BERTILLER monica Beatriz
artículos
Título:
Modeling high-frequency position data of large herbivores with a phase-state model.
Autor/es:
ARES, J.O.; BERTILLER, M.B
Revista:
ECOLOGICAL MODELLING
Editorial:
ELSEVIER SCIENCE BV
Referencias:
Año: 2010 vol. 221 p. 2323 - 2329
ISSN:
0304-3800
Resumen:
Understanding the rules and
factors that drive the foraging behavior of large herbivores is important to describe
their interaction with the landscape at various spatial scales. Some unresolved
questions refer to landscape?behavioral interactions that result in oriented or
random search in seasonally changing landscapes. Remotely sensed position data
indicate that herbivores select local patches of heterogeneous landscapes depending
on a complex host of dynamically varying animal and environmental conditions. Since
foraging paths consist in successions of relatively short steps, increasing the
frequency at which position information is acquired would contribute to
entangle the mechanisms resulting in herbivores? foraging paths. We addressed
the question whether herbivores would obtain information at a patch scale that
would modify their distribution at a landscape scale based on directed movement
or navigation ability. We considered a set of 100,000 high-frequency (1 min
intervals) position data of several free-ranging sheep (Ovis aries) at a
seasonal-varying range (Patagonian Monte, Argentina) and observed their
movements at landscape and at single vegetation patch scales. At a landscape
scale, we inspected the spatial co-variation of seasonally varying forage offer
and ewes? movement speeds. At a patch scale, we developed a phase-state (P-S)
model of movement cycles based on the occurrence of behavioral phases along
foraging paths, and fitted it to the observed daily time series of ewes?
movement speeds. Ewes were preferentially distributed in areas with high forage
offer during periods of low forage availability and the reverse occurred during
the season of high forage availability. Parameters of the model of activity
cycles amenable to control by ewes (duration of speed phases, time elapsed
between speed cycles) did not covariate with forage offer, but varied
significantly among ewes. The shape (kurtosis) parameter of the model of
movement cycles, one which is unlikely under ewes? control, co-varied Significantly with spatial forage offer but
did not differ among ewes. We conclude that ewes allocated foraging time along
a series of similar movement efforts irrespective of forage availability at
small patches. Average forage scarcity at multi-patch level increases the ratio
of searching to feeding time. This results in apparent selective time
allocation to richer forage areas but does not imply evidence for oriented movement
at a landscape scale. We advance a behavioral-based definition of forage
patches and discuss its implications in developing foraging theory and models.
The P-S model applied to high-frequency position data of large herbivores
substantially improves the interpretation of the factors controlling their time
allocation in space with respect to previous models of herbivore spatial
behavior by discriminating among behavioral-based and environmentally induced
components of their movements.