[Coral-List] Exotic, Introduced, Native....
J. Michael Nolan
mnolan at rainforestandreef.org
Sat Feb 16 15:15:11 EST 2013
Coral List Members.....
I did not think I summarized responses I got when I raised this topic to many lists. Was poking around today and see that I did a summary. Not sure it will add to this discussion or if any of it will translate to Coral Biology, but here it is. Kind of scary when you've saved so many things that you can't remember what you have. I have archived all kinds of video, NPR discussions, etc. on the topic. Obviously living on the eastern shores of Lake Michigan, it is always a big topic here. Have a great Saturday and weekend.
Mike Nolan....see below
Some months ago I raised this question to many lists. Here is the summary of responses I got.
Original question: At what point does an introduced species become
recognized as "native" to an ecosystem?
Thanks much to all from several lists that contributed.
1. The short answer is it doesn't. The term "native" will apply to
species as information degrades or is lost over time or if the correct
historical information has not been reported. Science and cladistics
allow us to answer questions about native origin and are reducing
questions and errors. When a species has been around for a long while
100's, thousands etc. years, in one area and is known to have been
introduced from another area, it is generally, mostly by the public or
non-science communities, referred to as naturalized. This term, however,
can be misleading.
The word "naturalized" is part of the continuum from introduction to
invasion and can have different definitions depending on the author(s).
Some folks use this term to refer to to a non-native or introduced
species that is not having apparent or a measurable ecological or
economic harm on it's introduced range.
2. In human history time frame introduced species may eventually be
"naturalized" but not a part of the native flora and fauna. What some
inquirers may be after is on a geologic time frame such as species
land bridges or colonizing island eons ago then those are "the native
species." My understanding is it comes down to time and introductions
the last few centuries (at least) and maybe even millennia (such as some
humanities ancient crops) are still considered introduced from an
and anthropological standpoint.
3. It never becomes native-The word native assumes that it evolved there
Scientists use the word "naturalized" to refer to those non-native
have incorporated themselves into the landscape and are not invasive.
invasive exotic infers that the introduced species is aggressively out
native species in the area. There is a difference between non-native
invasive exotic based on the impact to the habitat in which it was
4. An introduced species can never become "native" by definition. An
introduced species, once functioning without further input from new
introductions, can become "naturalized" but it will never be native.
"Naturalized" does not indicate whether it has reasonable sociobiology
or whether it is invasive.
5. > At what point does an introduced species become recognized as
> to an ecosystem?
In terms of modern invasion biology this does not happen. That is, no
one has ever "recognized" a known invader as native after any length of
time. However, when the geographic origin of a species is in doubt, it
is labeled "crytpic", meaning that we don't know whether its native or
not. I suppose you could answer the question with "when people forget
what was native", i.e. plants of North America that may have been
transported by pre-historic migrating humans were labeled as native when
we started to catalog them in modern times could fall into that
category. Projecting into the future, if the introduced species evolves
the new species could arguably be called native.
6. I don't believe there is a "scientific" answer to this question.
to me that a species has evolved in a particular ecosystem or ecosystems
response to environmental factors in that/those ecosystems. If we
definition, it is my opinion that no species introduced by man,
accidently, can become a "native". It might become "naturalized" (able
survive and reproduce in the new environment as are invasive exotics)
Response: This seems to imply that a species is native only if it
evolves in the
location where it is found, and that any species which arrives by
or other form of transport is not native. This is a very Eulerian
In particular, with global warming we can expect species to drift
the poles, so even though the entire ecosystem drifts polewards, can we
that the component species cease to be native?
Response from original No. 6: Apparently I responded too quickly without
choosing my words carefully enough. I do believe that by saying that a
species evolves in response to the environmental factors within an
ecosystem, I allowed for migration of an ecosystem or parts of an
ecosystem in response to stresses such as global climate change. Also
by saying that species introduced by man cannot become native I believe
that I allowed for other types of migration.
Response: Excellent question!
Further, what are the boundaries of "the" ecosystem? What are the
standards (is the standard) by which said boundary is defined?
Thanks to those who focus on the essentials.
Response: So humans are qualitatively different from, say, birds that
seeds through their guts? I doubt there's a scientific basis for such
7. I have not heard of them becoming referred to as native, but they do
refer to an introduced species that becomes" like" native as
naturalized, if I remember correctly from Plant Taxonomy many years
8. Out west (Phoenix, Arizona) that designation is part historical, part
ecological. For example, we have tamarisk trees classified as invasive,
they've been here a hundred years or so, but clog up the drainages and
drive out other more indigenous species. We also have mesquite trees,
which many think are also intrusive, but have been here at least 300
years and are part of the "natural landscape," at least that's how we
Any ecologists out there that can give us an official definition of
I'm very curious myself because I have my students working on a project
with local park rangers to help them identify, map and remove invasive
species from one of our Phoenix Mountain Preserves. The Rangers
perspective is rather arbitrary about what is invasive or native. They
are mostly concerned with the ecological impact of a species, not its
9. A species is native if it naturally occurs there, or was dispersed =
there, or if it is autochthonous. Introduced species means that the =
species was purposely or accidentally introduced by man.
These are semantics. The important thing is native vs. introduced and
then whether the species is naturalized.
Response: This seems like a confusing answer. Let me put a more specific
When there was a land bridge over the Bering Strait a lot of animals =
entered N. America from Asia. Does John's definition mean that a tick =
that arrived on a bear is native and one that arrived on a human is =
10. This is a question I have had for some time. I study coyote
Ohio, and people are continually pointing out to me that coyotes are not
native to the eastern United States and, therefore, "don't belong here."
However, coyotes have migrated here on their own, possibly 200+ years
What do we call that?
Response: Opportunism and (artificial?)
niche-filling? Resilience? Ripple-response to
perturbations? Adaptation? Too many feral and loose domestic
cats? Depression of other predator populations? Habitat
change? Increased study? Not enough study?
11. As I recall, once an introduced species begins reproducing in its
new environment it is considered "naturalized", but still not native.
12. I received this response from a professor at the University of
The terminology that I have heard used is they become "naturalized".
have a number of species in the US that have become naturalized to the
extent that most people think of them as native ... corn, soybeans,
.... many flowers and tree species that were introduced in the early
"whiteman" history of the US.
Response: thanks for the clarification. corn, of course, was originally
domesticated from teosinte in the new world, likely mexico, so it is as
native as they come!
13. I'm a planner, not an ecologist. But, from what I have learned over
the years, it would seem to me a species would only come to be known as
"native' when all records of its introduction/in-migration have been
lost. Until then, and as long as we can tell that it came from
elsewhere, it must at least be considered non-native. At best, it can
be thought of as adapted or naturalized, if it is able to co-exist with
endemic species. If that species is beating out native species in some
form of resource competition and reproductive success, then it is
14. From the various sources I've consulted, an introduced species never
becomes "native", as long as we know that indeed it
was originally from someplace else. So, the answer is never. BUT, an
introduced species can become "established" ie.
naturally sustaining itself in the new locale (this clearly can happen
pretty quick), and it can also become "naturalized". Not
sure of the exact definition is on this, but I believe its different
from established. When I have time, I'll look into it and pass it
15. Since we are discussing invasive species, I wanted to let you know
a project my class is participating in this year. It is called the
Purple Project. We are raising Galarucella beetles that will be
released in the Utica Marsh to try to reduce the spread of Purple
Loosestrife. If you want to see ongoing pictures of our project check
out my website. If you want to know more about the project check the
16. I believe the accepted standard for the United States is that a
species had to be here before the colonists arrived in order to be
17. From what I can determine, exotics don't become "native" they only
become "naturalized'. Botonists consider dandelions and Queen Anne's
Lace as naturalized because they were introduced when the first settlers
came to America and are now found nationwide. And then there are
cultivars and feral species....
This isn't definitive, but it has been my experience up to this point.
18. Continuing the thought-provoking invasive species
thread, I'm passing along this info about a recent
study finding an effect of an invasive plant on the
growth of native species.
Subje [Aliens-L] Invasive Plant Suppresses the Growth
of Native Tree
ct: Seedlings by Disrupting Belowground Mutualisms
PLoS Biology Volume 4 | Issue 5 | MAY 2006 --look for
it on the web
Invasive Plant Suppresses the Growth of Native Tree
Seedlings by Disrupting
Kristina A. Stinson, Stuart A. Campbell, Jeff R.
Powell, Benjamin E. Wolfe,
Ragan M. Callaway, Giles C. Thelen, Steven G. Hallett,
Daniel Prati, John
Harvard Forest, Harvard University, Petersham,
States of America, Department of Integrative Biology,
Guelph, Ontario, Canada, Division of Biological
Sciences, University of
Montana, Missoula, Montana, United States of America,
Department of Botany
and Plant Pathology, Purdue University, West
Lafayette, Indiana, United
States of America, Department of Community Ecology,
UFZ Centre for
Environmental Research, Halle, Germany
The impact of exotic species on native organisms is
but poorly understood. Very few studies have
empirically investigated how
invading plants may alter delicate ecological
interactions among resident
species in the invaded range. We present novel
evidence that antifungal
phytochemistry of the invasive plant, Alliaria
petiolata, a European
of North American forests, suppresses native plant
growth by disrupting
mutualistic associations between native canopy tree
belowground arbuscular mycorrhizal fungi. Our results
elucidate an indirect
mechanism by which invasive plants can impact native
flora, and may help
explain how this plant successfully invades relatively
Abbreviations: AMF, arbuscular mycorrhizal fungi;
ANOVA, analysis of
variance; REGW, Ryan-Einot-Gabriel-Welsch
Widespread anthropogenic dispersal of exotic organisms
has raised growing
concern over their devastating ecological impacts, and
has prompted decades
of research on the ecology of invasive species [1-3].
Exotic plants may
become aggressive invaders outside their home ranges
for a number of
reasons, including release from native, specialized
antagonists , higher
relative performance in a new site , direct
interference with native plant performance , and
variability in the
responses and resistance of native systems to invasion
successful invasion in many cases appears to involve
the fact that invasive
species are not at equilibrium, and are either freed
interactions with their enemies in the home range,
interactions among the suite of native organisms they
encounter in a new
range . Nevertheless, experimental data on
species-level impacts of
exotic plants are still limited . One particularly
understudied area is
the potential for invasive plants to disrupt existing
associations within native communities [6,10]. Many
exotic and native
alike depend upon mutualisms with native insects,
birds, or mammals for
pollination and seed dispersal , and with soil
microbes for symbiotic
nutrient exchange . Thus, when an introduced
species encounters a new
suite of resident organisms, it is likely to alter
ecological relationships, many of which have
co-evolved within native
One such relationship is that between plants and
mycorrhizal fungi .
Most vascular plants form mycorrhizal associations
mycorrhizal fungi (AMF) , and many plants are
highly dependent on this
association for their growth and survival ,
perennials and others found in late-successional
communities . In
contrast, many weedy plants, in particular
non-mycotrophic plants, can be
negatively affected by AMF [14-16]. Naturalized exotic
plants have been
found to be poorer hosts and depend less on native AMF
than native plants
. They often colonize areas that have been
disturbed , and
disturbances to soil have been shown to negatively
impact AMF functioning
. Furthermore, it has been proposed that the
proliferation of plants
with low mycorrhizal dependency may degrade AMF
densities in the soil .
However, a few invasive plants proliferate in the
understory of mature
temperate forests , where AMF density is typically
high . The
existing mycelial network in mature forest soils may
establishment of exotic, mycorrhizal-dependent,
recruits [20,21], but this
should not be the case for non-mycorrhizal invaders.
invasive plants establish and degrade AMF in mature
forests, then the
effects on certain resident native plants could be
One of the most problematic invaders of mesic
temperate forests in North
America is Alliaria petiolata (garlic mustard;
non-mycorrhizal, shade-tolerant, Eurasian biennial
herb which, like most
other mustards, primarily occupies disturbed areas.
Garlic mustard is
abundant in forest edges, semishaded floodplains, and
other disturbed sites
in its home range . However, this species has
recently become an
aggressive and widespread invader of both disturbed
areas and closed-canopy
forest understory across much of the United States and
Canada , where
apparently suppresses native understory plants,
including the seedlings of
dominant canopy trees [22,24]. The mechanism
underlying garlic mustard's
unusual capacity to enter and proliferate within
intact North American
forest community has not yet been established.
As shown in recent greenhouse experiments, garlic
mustard's impact on
native understory flora may involve competitive 
on native plants , but it has also been
hypothesized that this species
interferes with plant-AMF interactions in its invaded
range . Members
the Brassicaceae, including garlic mustard, produce
various combinations of
glucosinolate products , organic plant chemicals
anti-herbivore, anti-pathogenic and allelopathic 
properties, that may
also prevent this non-mycorrhizal plant family from
associating with AMF
. These phytochemicals may be released into soils
as root exudates, as
result of damaged root tissue, or in the form of leaf
of garlic mustard in the field correlate with low
inoculum potential of
and extracts of garlic mustard leaves have been shown
to reduce the
germination of AMF spores and impair AMF colonization
of cultivated tomato
roots in laboratory settings . Although not all
invasive, it is possible that garlic mustard's
successful invasion of
understory habitats involves the negative effects of
its phytochemistry on
the native plant and AMF species it encounters outside
its home range.
Others have shown that exotic plants can recruit
different suites of
microbial organisms in their new ranges that can be
antagonistic to native
plants . However, to our knowledge, no previous
studies have directly
tested whether this species or any other exotic plant
plant-AMF mutualisms within natural communities. Here,
we present novel
evidence that garlic mustard negatively impacts the
growth of AMF-dependent
forest tree seedlings by its disruption of native
We further show that, because seedlings of dominant
tree species in mature
forest communities are more highly dependent on AMF
than plants that
typically dominate earlier successional communities,
invasion may disproportionately damage mature forests
relative to other
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