Animal Movement - Mobility Data - page 277

Table 13.1 Types of Tags, Sampling Schedules Often Used, and Type of Analysis
Performed. Geolocators Use Light Pattern to Compute Length of the Day (from which
One Derives Latitude) and the Time of Solar Noon (Used to Compute Longitude).

Sampling Type of Movement

Type of Mark Sampling Density Schedule Analyzed

Tag Low (usually 2 are On occasion Migration

available) Dispersal

VHF Intermediate (e.g., Systematic (only Home range

1 spatio-temporal daytime with Habitat selection

position per some days) airplanes)

Geolocator 1 per day Systematic Migration

GPS 1 each few hours Systematic Home range

Habitat selection
Migration
Dispersal

GPS 1 each few minutes Systematic Search behavior

trajectories. Movement tactics typically vary as a function of environmental
conditions. In practice, good precision in reconstructing individual animal tra-
jectories is necessary to increase the power of statistical tests. Ecologists are
interested in describing patterns, but especially in understanding the processes
below spatio-temporal patterns, so that statistical inference is the fundamental
tool to be used. Models allow us to deal with ecological complexity at different
scales. Two axes are relevant: the temporal scale of the explanation (proximate
versus ultimate) and the sampling unit that goes from the individual to the pop-
ulation through kin and social groups. Orientation mechanisms, dispersal, and
foraging are typically individual-specific but causes operate at different tempo-
ral scales (say, minutes, years, and generations). Population diffusion, spatial
distribution, and interactions determine ecosystem complexity and biodiversity,
that is, their long term properties. There are also intermediate processes: a typ-
ical home range lasts for the life span of each individual and is determined
by its energetic needs but also by local interactions with neighbors. Movement
analysis has the potential to unify these different aspects.

13.2.4 Data Sampling

In ecology an appropriate sampling design is the foundation of good science but
its importance is often overlooked. Table 13.1 summarizes the different options,
because technology, sampling design, and aims of the research are interlaced.
There is a trade-off between the cost of the tracking device and sample size. For
instance, tags are very cheap but to obtain reliable results one needs many hun-
dreds or thousands of marked animals. The use of a systematic sampling schedule