196
P. Thiriet et al.
From these considerations, chase tactic does not seem to be suitable in highly
complex habitats, while ambush tactic does. It is less clear-cut for stalk-attack tactic.
Some predators are able to use only one tactic (specialist) while some others are
able to use several tactics (generalist) depending on the environment. The relation
between habitat and predation tactic suitability is probably a strong driver of distribution patterns of specialist predators among habitats (habitat-specific predators)
(Schultz et al. 2009). Dealing with this, predation mortality of juveniles in a given
habitat depends on its ability to escape the habitat-specific predators, by using different strategies such as particular microhabitat use (see Box 5). Thus, in general,
coevolution between habitat-specific predator and prey juveniles results in specialized escape strategies (see Abrams 1990; Lima 1992). This specialization in escape
strategy would lead the prey to actively choose for, and/or to better survive in, the
habitat of its coevolved predator rather than another habitats where it has less ability
to escape from predators practicing other tactics (Lima 1992).
12.6 Synergy Between Habitats: The So Called ‘Edge Effect’
Previous sections report that each habitat composing the seascape has its own functioning (mediated in part by its structural complexity) what results in differential
abundance patterns. However, at the boundary between two habitats (i.e. ecotone),
their respective functioning affect each other and particular abundance patterns may
appear in this transition area (usually higher diversity and abundance than both sides
added), this phenomena is called the edge effect (Ries et al. 2004). Global increase in
habitat fragmentation and its propensity to increase the amount of ecotone and consequently edge effects (Smith 2011) stresses the need to better understand underlying
mechanisms.
Edge effect may come from emergent physical properties. For instance, at ecotone
between marcophyte-formed habitat and bare substrate, current flow and turbulence
are reduced. This may cause accumulation of swarming hyper-benthic invertebrates
(such as mysids) and therefore offer a great opportunity for juveniles to forage
(Macreadie et al. 2010).
Edge effect may also come from the complementarities of resources level proper to
each habitat. At ecotone, mobile organisms may regularly switch between habitats
and therefore exploit alternatively the optimum habitat as regard to the resource
expected (basically food or shelter). For instance, one habitat may be optimum
for foraging activities but with a higher predation risk than another habitat. At the
ecotone, juvenile therefore can forage efficiently in the risky habitat and switch when
a predator is detected. Interaction between predator tactic and structural complexity
may also result in positive edge effect for prey juveniles which have developed
adaptative anti predator behavior (Matsuda et al. 1993). Positioned close to the
ecotone between a highly complex habitat and an open habitat, juvenile may escape
in the suitable habitat as regard to the tactic of the predator detected (see section
above for details about habitat-specific predators) (Martin et al. 2010; Smith et al.
2011).
P. Thiriet et al.
From these considerations, chase tactic does not seem to be suitable in highly
complex habitats, while ambush tactic does. It is less clear-cut for stalk-attack tactic.
Some predators are able to use only one tactic (specialist) while some others are
able to use several tactics (generalist) depending on the environment. The relation
between habitat and predation tactic suitability is probably a strong driver of distribution patterns of specialist predators among habitats (habitat-specific predators)
(Schultz et al. 2009). Dealing with this, predation mortality of juveniles in a given
habitat depends on its ability to escape the habitat-specific predators, by using different strategies such as particular microhabitat use (see Box 5). Thus, in general,
coevolution between habitat-specific predator and prey juveniles results in specialized escape strategies (see Abrams 1990; Lima 1992). This specialization in escape
strategy would lead the prey to actively choose for, and/or to better survive in, the
habitat of its coevolved predator rather than another habitats where it has less ability
to escape from predators practicing other tactics (Lima 1992).
12.6 Synergy Between Habitats: The So Called ‘Edge Effect’
Previous sections report that each habitat composing the seascape has its own functioning (mediated in part by its structural complexity) what results in differential
abundance patterns. However, at the boundary between two habitats (i.e. ecotone),
their respective functioning affect each other and particular abundance patterns may
appear in this transition area (usually higher diversity and abundance than both sides
added), this phenomena is called the edge effect (Ries et al. 2004). Global increase in
habitat fragmentation and its propensity to increase the amount of ecotone and consequently edge effects (Smith 2011) stresses the need to better understand underlying
mechanisms.
Edge effect may come from emergent physical properties. For instance, at ecotone
between marcophyte-formed habitat and bare substrate, current flow and turbulence
are reduced. This may cause accumulation of swarming hyper-benthic invertebrates
(such as mysids) and therefore offer a great opportunity for juveniles to forage
(Macreadie et al. 2010).
Edge effect may also come from the complementarities of resources level proper to
each habitat. At ecotone, mobile organisms may regularly switch between habitats
and therefore exploit alternatively the optimum habitat as regard to the resource
expected (basically food or shelter). For instance, one habitat may be optimum
for foraging activities but with a higher predation risk than another habitat. At the
ecotone, juvenile therefore can forage efficiently in the risky habitat and switch when
a predator is detected. Interaction between predator tactic and structural complexity
may also result in positive edge effect for prey juveniles which have developed
adaptative anti predator behavior (Matsuda et al. 1993). Positioned close to the
ecotone between a highly complex habitat and an open habitat, juvenile may escape
in the suitable habitat as regard to the tactic of the predator detected (see section
above for details about habitat-specific predators) (Martin et al. 2010; Smith et al.
2011).