WEWeb EcologyWEWeb Ecol.1399-1183Copernicus GmbHGöttingen, Germany10.5194/we-14-85-2014Demography gone wild in native species: four reasons to avoid the term “native invaders”MéndezM.marcos.mendez@urjc.esEscuderoA.IriondoJ. M.ViejoR. M.Área de Biodiversidad y Conservación, Universidad Rey
Juan Carlos, c/ Tulipán s/n., 28933 Móstoles, Madrid, SpainM. Méndez (marcos.mendez@urjc.es)14January2015141858714October20143December20144December2014This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://we.copernicus.org/articles/14/85/2014/we-14-85-2014.htmlThe full text article is available as a PDF file from https://we.copernicus.org/articles/14/85/2014/we-14-85-2014.pdf
The definition
and application of the concepts “invasive” and “invader” have been a
subject of discussion among ecologists for over a decade and, as a
consequence, different authors have suggested a panoply of terms to cover all
the situations (Davis and Thompson, 2000; Richardson et al., 2000; Colautti
and MacIsaac, 2004; Blackburn et al., 2011; Kowarik and Pyšek, 2012).
Typically, further dispersal and increase in numbers after arrival in a new
territory have been considered fundamental in this terminology (Richardson et
al., 2000; Colautti and MacIsaac, 2004; Wilson et al., 2009; Richardson and
Ricciardi, 2013). In our view, the use of the term “native invaders” adds a
discomforting twist to this apparently settled controversy.
“Native invaders” is a label recently introduced (Valéry et al., 2008;
Simberloff, 2011) to designate “species that have become “invasive” in
their own native range” (Carey et al., 2012).
Native invaders have, according to this definition, increased in numbers so
as to become a nuisance. We will refer to this situation as demographic
disregulation. This is what Valéry et al. (2008) consider the core aspect
of invasiveness, while they dismiss human transport to a new territory as
irrelevant. Although this situation clearly presents management challenges,
recently reviewed by Carey et al. (2012), we question the need and
convenience of the term “native invader”. From a purely semantic view, the
available terminology can account for all cases of demographic disregulation
of natural populations, both within and beyond their historical range. For
example, in the botanical literature, “apophyte” – a term that can be
traced back at least to the late 1960s (Holub and Jirásek, 1967),
although not widely utilized – refers to species which increase their
numbers or modify their demographic cycles within their ranges due to
anthropogenic causes. Thus, the framework proposed by Richardson et
al. (2000) and Didham et al. (2005) covers what most researchers consider
non-indigenous naturalized and invasive species. Terms for the diffusion-like
expansion of populations beyond their historical range have also been
considered by Davis and Thompson (2000).
Some researchers consider terminological controversies to be purely semantic
and trivial. By contrast, we contend that labelling some native species as
invaders has deep management implications, because they directly affect how
invasiveness is conceived. We believe that emphasizing demographic increase,
while dismissing previous anthropogenic dispersal (Valéry et al.,
2008), does not convey an appropriate conceptualization of
invasion biology on four grounds: (1) it adds nothing to an already
well-known management problem, (2) it can bias the perception of management
options of some stakeholders and create more damage than benefit, (3) it
neglects the fact that different
causes underlie the disregulation of native and non-indigenous species, and
(4) it deliberately excludes some species that can also become disregulated
for anthropogenic reasons, thus adding to the confusion. We elaborate on
these four criticisms below.
Deterioration of ecosystem services and other economic drawbacks caused by
anthropogenically disregulated native populations is already well known among
scientists and managers. A few examples from the Iberian Peninsula where we
work are the management of wildboar Sus scrofa populations lacking
predators (Sáez-Royuela and Tellería, 1986), of seagulls
Larus cachinnans getting extra food supplies from human waste (Vidal
et al., 1998), of magpies Pica pica dominating bocage landscapes
(Díaz-Ruiz et al., 2010) or amphibian extinction by brown trout
Salmo trutta stocked in fishless ponds (Orizaola and Braña,
2006). A new, catchy name for an old problem contributes little or nothing to
solving it. On the contrary, this term can easily be pushed to absurd
extremes. For example, pine species which have been deliberately stocked in
their native area beyond historical numbers and which strongly influence the
natural fire regime in Mediterranean areas (Barbero et al., 1990) could be
considered native invaders.
Furthermore, using the value-laden “invader” in these cases can tip the
balance against some species perceived as a nuisance by some influential
stakeholders. Are the shags Phalacrocorax carbo really so damaging
for the already overexploited salmon fisheries in the northern Iberian
Peninsula (Álvarez, 2009)? Should the wolf, Canis lupus, which
is regaining its historically lost quarters in the central and eastern
Iberian peninsula (Alonso et al., 2012), be considered a native invader? Once
the label “invader” is attached to a species, perception can be dangerously
biased. This can be particularly misleading in regions such as the
Mediterranean Basin, where man-induced changes go back for more than 8000
years. What is the reference ecosystem to use in order to decide if a
particular species is rapidly spreading in a disregulated way or simply
recovering a past equilibrium (Balaguer et al., 2014)?
What can be learnt from pooling native and non-indigenous demographically
successful species under a common label? We believe that the underlying
ecological processes and the consequences derived from the demographic
expansion within or beyond a species' historical range are
so different that pooling them under the same term is misleading (see
Richardson and Ricciardi, 2013, for a similar reasoning). For example, the
important distinction between drivers and passengers (Didham et al., 2005)
developed for non-indigenous invaders is of little use for native invaders;
all native invaders are passengers, or collateral damages of human
alterations of the environment. By definition, there is no such thing as a
driver native invader, because a historically abundant species is not
perceived as an invader, but as an abundant species. Furthermore, the
possibilities of controlling the disregulated demography of a species differ
greatly among native and non-indigenous invaders. Historical adjustment to
abiotic factors and natural enemies is radically different among native and
non-indigenous invaders (Wilson et al., 2009), and leads to important
evolutionary differences (Colautti and MacIsaac, 2004). Non-indigenous
invaders lack a coevolutionary history that is present in native invaders,
although non-indigenous species are liable to evolve rapidly in the invaded
territory (Cox, 2004).
Finally, the term “native invader” deliberately excludes those populations
showing recurrent increases in numbers (Simberloff, 2011). However, those
species could modify their peak numbers or the frequency of demographic
increases as a consequence of anthropogenic modifications of the environment.
They are as liable to become nuisance species as any other native,
anthropogenically disregulated species.
Native disregulated populations pose a management challenge that will
potentially increase in the current scenario of global change (Battisti et
al., 2005). However, we discourage the use of “native invader”, as it does
not suggest any fruitful management guideline, may lead to wrong management
decisions, and potentially hinder the advancement of invasion biology
research.
Acknowledgements
We thank Lori J. De Hond for her linguistic assistance. This work was
partially financed by Project MOUNTAINS (CGL2013-38427) financed by the
Spanish Government. Edited by: D. Montesinos
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