The evolution of increased competitive ability (EICA) hypothesis was first proposed by Bernd Blossey and Rolf Nötzold in 1995 as a way to explain the success of invasive,
non-indigenous species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...
(in particular, plants). Observing that:
# there is usually a lag period between the time of introduction of an
invasive species
An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species ad ...
and the point at which it is considered invasive, and
# invasive plants seem to be more virulent in habitats into which they have been introduced (as compared to their native habitats), the scientists presumed a sort of
naturalization
Naturalization (or naturalisation) is the legal act or process by which a non-citizen of a country may acquire citizenship or nationality of that country. It may be done automatically by a statute, i.e., without any effort on the part of the in ...
through modification for non-indigenous plants.
Because of a lack of native
predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
, the scientists reasoned, introduced plants are able to reallocate resources from defense mechanisms into growth and development. Introduced plants can thereby
evolve to grow taller, produce more
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
, and yield more
viable offspring than their native counterparts, according to the hypothesis.
Blossey and Nötzold tested their hypothesis on ''
Lythrum salicaria
''Lythrum salicaria'' or purple loosestrifeFlora of NW Europe''Lythrum salicaria'' is a flowering plant belonging to the family Lythraceae. It should not be confused with other plants sharing the name loosestrife that are members of the family Pr ...
'' (purple loosetrife) by potting seeds from plants growing in Ithaca, New York, U.S.A., and Lucelle, Switzerland. The seeds were allowed to
germinate
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...
in a lab at Christian-Albrechts University in Kiel, northern Germany, and observed for two years. True to the predictions of the EICA Hypothesis, the plants derived from Ithaca produced significantly more biomass that the plants derived from Lucelle. The ''Lythrum salicaria'' plants derived from Ithaca also grew taller and were significantly less resistant to the root-feeding
weevil
Weevils are beetles belonging to the Taxonomic rank, superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and Herbivore, herbivorous. Approximately 97,000 species of weevils are known. They b ...
present over its native range.
Significance
Unlike the notable ideas (concerning the success of invasive non-indigenous organisms) that preceded it, such as the
enemy release hypothesis The enemy release hypothesis is among the most widely proposed explanations for the dominance of exotic invasive species. In its native range, a species has co-evolved with pathogens, parasites and predators that limit its population. When it arri ...
(ERH) and
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
's
Habituation Hypothesis, the EICA hypothesis
postulate
An axiom, postulate, or assumption is a statement that is taken to be true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Ancient Greek word (), meaning 'that which is thought worthy or f ...
s that an invasive species is ''not'' as fit (in its introduced habitat) at its moment of introduction as it is at the time that it is considered invasive. As suggested by the name of the hypothesis (Evolution of Increased Competitive Ability), the hypothesis predicts that much of the invasive potential of an invasive species is derived from its ability to evolve to reallocate its resources.
This idea is troubling in that it adds a new variable to "invasive potential", making it harder to predict whether or not a species will become invasive if it is introduced into a new area. In other words, the EICA hypothesis presents a new environmental safety concern. If its postulates hold, in the long run,
introduced species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...
may have to be more highly regulated than they are at present, because no set of
traits or pattern of introduction can predict the extent to which an organism can reallocate its resources in response to a release from stress.
Scientific support and revision
Since its debut in 1995, Bernd Blossey and Rolf Nötzold's paper, "Evolution of increased competitive ability in invasive nonindigenous plants: a hypothesis" has been met with varying degrees of enthusiasm. The paper has been cited over 1000 times as of September, 2021 in
scientific journals
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research.
Content
Articles in scientific journals are mostly written by active scientists such as s ...
, including
review articles
A review article is an article that summarizes the current state of understanding on a topic within a certain discipline. A review article is generally considered a secondary source since it may analyze and discuss the method and conclusions ...
, tests of the hypothesis using different
model species
A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...
, and expansions and reformulations of the hypothesis. Among the model species on which the hypothesis has been evaluated most recently (in its original form) are ''
Solidago gigantea
''Solidago gigantea'' is a North American plant species in the family Asteraceae. Its common names include tall goldenrod and giant goldenrod, among others.
Goldenrod is the state flower of Kentucky, and ''Solidago gigantea'' is the state flowe ...
'' (giant goldenrod), ''
Sapium sebiferum
''Triadica sebifera'' is a tree native to eastern China. It is commonly called Chinese tallow, Chinese tallowtree, Florida aspen, chicken tree, gray popcorn tree, or candleberry tree.
The seeds (as well as from those of '' Triadica cochinchine ...
'' (Chinese Tallow), and ''
Lepidium draba
''Lepidium draba'', the whitetop or hoary cress, or Thanet cress, is a rhizomatous perennial flowering plant in the family Brassicaceae. It is native to western Asia and southeastern Europe and widely introduced elsewhere.
Description
Whiteto ...
'' (whitetop). Of these three model species, the success and behavior of ''Sapium sebifurum'' agreed most closely with the postulates of the EICA Hypothesis, according to the researches conducting the study. In its study, the success and behavior of ''Solidago gigantea'' was only partially explained by the EICA hypothesis, according to its researchers. ''Lepidium draba'' did not seem to follow any of the postulates of the EICA Hypothesis, as the researchers of the study understood them.
Through most of the studies done on the EICA Hypothesis (see examples above), it holds that the introduced populations of invasive plant species are less able to cope with the pressures of specialist
herbivores
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
than native populations of the same species are, suggesting that invasive species ''do'' respond to accelerated
natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
after being released from the
selective pressure
Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...
of specialist herbivores and ''do'' have the potential to reallocate resources away from specific forms of defense. However, not all of these introduced populations produce significantly more biomass than the native populations of the same species under laboratory conditions. A study conducted by Bossdorf et al. in 2004 on ''Alliaria petiolata'' (garlic mustard)
may lend some insight into this discrepancy. Bossdorf et al. potted seeds from native and introduced populations of ''Alliaria petiolata'' and put them in direct competition with one another in a laboratory setting (i.e. the native and introduced populations were grown on in the same pot of soil, and subjected to the same treatments), and found that in direct competition, the native populations were able to out-compete the invasive populations. Bossdorf et al. proposed that this observation could result from the fact that there is a
fitness cost to traits that increase so-called "competitive ability". Under this assumption, invasive populations of ''Alliaria petiolata'' had evolved a higher fitness (similar to ''Lythrum Salicaria'') in their introduced ranges at the cost of certain defense mechanisms ''and'' at the cost of certain aspects of growth and development (dissimilar to ''Lythrum Salicaria''). It could be, therefore, that the EICA Hypothesis is too narrow in scope, and should be reworded to place an emphasis on an invasive species' ability to reallocate its resources in order to procure a fitness advantage that may or may not involve more vigorous growth and development.
References
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Botany
Ecology
Evolutionary biology