Trait structure reveals the processes underlying fish establishment in the Mediterranean
Abstract
Aim Typically, non-indigenous species have been studied in relation to either
the invaded (recipient) community or the donor community. However, we still
lack a broad understanding of the mechanisms underlying the establishment of
non-indigenous species that combines both perspectives. Since the opening of
the Suez Canal, hundreds of species have invaded the Mediterranean from the
Red Sea, forming a unique system in which the entire species pool (donor,
non-indigenous and recipient) is known. Focusing on species ecological traits,
we assess the drivers underlying the establishment of non-indigenous species
from the onset of the invasion to the present.
Location The Mediterranean and Red Seas.
Methods We compiled traits for shallow-water hard-bottom-associated fishes
in the Mediterranean (recipient community) and the Red Sea (donor
community). We compared the multivariate community trait structure of nonindigenous
species with the donor and recipient assemblages, using a novel
method to objectively assign trait-weights, thereby increasing the robustness of
the results. Patterns were contrasted with two types of null models which
provide distinct insights into the ecological processes.
Results Non-indigenous fishes are very diverse ecologically, substantially
increasing the total community trait diversity of the Mediterranean. Trait
similarity between non-indigenous and indigenous Mediterranean species was
lower than expected, indicating that non-indigenous fishes tend to occupy
relatively vacant niches within the Mediterranean. However, we further found
that over time non-indigenous species display increased trait similarity to
indigenous Mediterranean species. This suggests that trait constraints
associated with successful establishment are weakening.
Main conclusions Non-indigenous species establish in relatively vacant
ecological niches, opening the possibility for predicting establishment using
ecological traits. However, the weakening of trait constraints through time suggests
that forecasting future establishment may be difficult. Faced with an accelerating
pace of invasion, it appears that the Mediterranean is going to be transformed into
an extension of the Red Sea in terms of trait and species composition.