Carrying capacity in arid rangelands during droughts: the role of temporal and spatial thresholds
Authored by F Accatino, D Ward, K Wiegand, Michele C De
Date Published: 2017
DOI: 10.1017/s1751731116001531
Sponsors:
German Federal Ministry of Education and Research (BMBF)
Platforms:
No platforms listed
Model Documentation:
ODD
Flow charts
Mathematical description
Model Code URLs:
Model code not found
Abstract
Assessing the carrying capacity is of primary importance in arid
rangelands. This becomes even more important during droughts, when
rangelands exhibit non-equilibrium dynamics, and the dynamics of
livestock conditions and forage resource are decoupled. Carrying
capacity is usually conceived as an equilibrium concept, that is, the
consumer density that can co-exist in long-term equilibrium with the
resource. As one of the first, here we address the concept of carrying
capacity in systems, where there is no feedback between consumer and
resource in a limited period of time. To this end, we developed an
individual-based model describing the basic characteristics of a
rangeland during a drought. The model represents a rangeland composed by
a single water point and forage distributed all around, with livestock
units moving from water to forage and vice versa, for eating and
drinking. For each livestock unit we implemented an energy balance and
we accounted for the gut-filling effect (i.e. only a limited amount of
forage can be ingested per unit time). Our results showed that there is
a temporal threshold above which livestock begin to experience energy
deficit and burn fat reserves. We demonstrated that such a temporal
threshold increases with the number of animals and decreases with the
rangeland conditions (amount of forage). The temporal threshold
corresponded to the time livestock take to consume all the forage within
a certain distance from water, so that the livestock can return to water
for drinking without spending more energy than they gain within a day.
In this study, we highlight the importance of a time threshold in the
assessment of carrying capacity in non-equilibrium conditions.
Considering this time threshold could explain contrasting observations
about the influence of livestock number on livestock conditions. In case
of private rangelands, the herd size should be chosen so that the
spatial threshold equals (or exceeds) the length of the drought.
Tags
Landscape
cattle
Heterogeneity
Foraging
patterns
Savanna
Drought
Population-dynamics
Nonequilibrium
Rainfall
Watering points
Herbivores
Optimal herd size
Water point
Energy deficit