structure, and function that underlie biological communities (Post and Palkovacs
2009). Consequently, biological invasions present unique opportunities to explore
the processes that govern the assembly of these interactions and their impact on
population demography and community structure. Many hypotheses in invasion
ecology invoke biotic interactions (Table 14.1), though ultimately, they come
down to the same three processes (mutualism, commensalism or parasitism): during
the introduction process, some interactions might be lost if there is no
co-introduction, but novel interactions might develop through ecological fitting or
co-xenic associations.
14.1.1 Ecological Fitting, Co-xenic Associations,
and Co-introductions
The act of moving a species across a biogeographical barrier often means that it will
lose key biotic interactions that were present in its native range, but experience a
whole suite of new interactions in its alien range. These effects might enhance
performance in the new environment, or provide obstacles to establishment and
subsequent success (Enders et al. 2018). For example, a reduction in, or more
frequently, the total absence of, specialist enemies following introduction can
allow individuals of a species in the alien range to realise greater reproductive output
than individuals in their native source populations (the Enemy Release Hypotheses—ERH, Colautti et al. 2004; see Table 14.1 for a summary of the hypotheses
mentioned throughout this chapter). In general, alien species can reassemble biotic
interactions through: (1) novel associations with organisms native to the new
environment (so-called ecological fitting; Le Roux et al. 2017); (2) associations
between organisms that are both alien to the new environment, but that do not
co-occur in their respective native ranges (so-called co-xenic associations; Nuñez
and Dickie 2014); or (3) co-introduction of interacting partners (the so-called
co-introduction pathway; Le Roux et al. 2017).
All biotic interactions span a continuum of specificity from the viewpoint of both
interacting partners. At the one end of the spectrum, highly specialised interactions
are characterised by those restricted to two species, or even biotypes. On the other
hand, some organisms can interact effectively with a range of different partners,
i.e. being generalists. For mutualistic interactions required for the successful completion of an organism’s life cycle, such as pollination, levels of specialisation will
have significant impacts on the establishment success of alien species following
introduction into new environments when not co-introduced. The loss of highly
specialised mutualists may hamper establishment success (i.e. Missed Mutualisms
Hypothesis; Catford et al. 2009). This was the case for many Pinus species introduced to the southern Hemisphere in previous centuries, where invasions only
occurred after pine-specific mycorrhizal fungi were introduced (e.g. Richardson
et al. 1994). The loss of generalist interactions intuitively poses less pivotal
14 Biotic Interactions as Mediators of Biological Invasions
389
2009). Consequently, biological invasions present unique opportunities to explore
the processes that govern the assembly of these interactions and their impact on
population demography and community structure. Many hypotheses in invasion
ecology invoke biotic interactions (Table 14.1), though ultimately, they come
down to the same three processes (mutualism, commensalism or parasitism): during
the introduction process, some interactions might be lost if there is no
co-introduction, but novel interactions might develop through ecological fitting or
co-xenic associations.
14.1.1 Ecological Fitting, Co-xenic Associations,
and Co-introductions
The act of moving a species across a biogeographical barrier often means that it will
lose key biotic interactions that were present in its native range, but experience a
whole suite of new interactions in its alien range. These effects might enhance
performance in the new environment, or provide obstacles to establishment and
subsequent success (Enders et al. 2018). For example, a reduction in, or more
frequently, the total absence of, specialist enemies following introduction can
allow individuals of a species in the alien range to realise greater reproductive output
than individuals in their native source populations (the Enemy Release Hypotheses—ERH, Colautti et al. 2004; see Table 14.1 for a summary of the hypotheses
mentioned throughout this chapter). In general, alien species can reassemble biotic
interactions through: (1) novel associations with organisms native to the new
environment (so-called ecological fitting; Le Roux et al. 2017); (2) associations
between organisms that are both alien to the new environment, but that do not
co-occur in their respective native ranges (so-called co-xenic associations; Nuñez
and Dickie 2014); or (3) co-introduction of interacting partners (the so-called
co-introduction pathway; Le Roux et al. 2017).
All biotic interactions span a continuum of specificity from the viewpoint of both
interacting partners. At the one end of the spectrum, highly specialised interactions
are characterised by those restricted to two species, or even biotypes. On the other
hand, some organisms can interact effectively with a range of different partners,
i.e. being generalists. For mutualistic interactions required for the successful completion of an organism’s life cycle, such as pollination, levels of specialisation will
have significant impacts on the establishment success of alien species following
introduction into new environments when not co-introduced. The loss of highly
specialised mutualists may hamper establishment success (i.e. Missed Mutualisms
Hypothesis; Catford et al. 2009). This was the case for many Pinus species introduced to the southern Hemisphere in previous centuries, where invasions only
occurred after pine-specific mycorrhizal fungi were introduced (e.g. Richardson
et al. 1994). The loss of generalist interactions intuitively poses less pivotal
14 Biotic Interactions as Mediators of Biological Invasions
389