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of mechanistic models of home range. A mechanistic approach implies that the
researcher is able to formulate competing models based on hypotheses about the
action of causal factors on animal movement.
The tactic used by the animal to invest time in different parts of the home
range is called habitat selection. Habitat selection represents a differential use of
a resource with respect to its availability. It is usually evaluated as a hierarchical
process at different levels. The first order selection or level is the selection of a
geographical range by a species, the second level is the selection of the home
range with respect to the range typical of the species, the third level is the
selection of different habitats within the home range, and the fourth level is the
selection of a resource item (typically food) within the habitat. More specifically,
it refers to a hierarchical process of behavioral responses that may result in the
disproportionate use of habitats with respect to their availability. Finally, habitat
selection studies have taken advantage of the development of generalized mixed
model platforms, which allow researchers obtain realistic and assumption-free
models for habitat selection.
Optimization of resource acquisition is analyzed by optimal foraging theory.
In the classical approach, OFT describes the optimal use of resources after
they have been found by the animal (post-encounter processes). A new and
interesting field of research deals with the problem of optimal search (pre-
encounter processes).
The analysis of the different kinds of animal movements has received a
formidable boost by technological development. Recording animal movement
under natural conditions (known as
animal tracking
) is fundamental to under-
standing why and how animals move. Even today this task is not trivial. The
first important breakthrough was represented by the development of very high
frequency (VHF) telemetry. Animals are fitted with transmitting devices, the
signal is recorded by a receiver, and the spatio-temporal position (which in
ecological literature is referred to as “a fix”) of the animal is obtained using
different methods, mainly based on triangulation. This approach, albeit valu-
able, present several shortcomings. In the earliest times, VHF telemetry was
more amenable for terrestrial than flying animals due to the weight of trans-
mitters, but now VHF transmitters have been fitted even on insects (e.g., large
grasshoppers). The major limitation is represented by the need of operators to
retrieve the signal, who may in turn “lose” animals when the animals are moving
quickly. Therefore, VHF telemetry was especially useful for animals residing in
a known area, while the collection of long range displacements was quite diffi-
cult, missing most of the migratory or dispersing movements. In the 1980s the
development of Platform Terminal Transmitters (PPTs) to uplink data to Argos
satellites (using Doppler-based positioning to compute animal locations) pro-
duced the first records of wide-range movements of marine mammals and birds
(note that to contact the satellite the device must to be outside water), but the true
