Ecological fitting

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Solanum tuberosum, an introduced relative of its original Solanum hosts, as a result of ecological fitting.[1]

Ecological fitting is "the process whereby organisms colonize and persist in novel environments, use novel resources or form novel associations with other species as a result of the suites of traits that they carry at the time they encounter the novel condition".

abiotic environment seem to indicate a history of coevolution, when in actuality the relevant traits evolved in response to a different set of biotic and abiotic conditions.[2]

The simplest form of ecological fitting is resource tracking, in which an organism continues to exploit the same resources, but in a new host or environment. In this framework, the organism occupies a multidimensional operative environment defined by the conditions in which it can persist, similar to the idea of the

Hutchinsonian niche.[3] In this case, a species can colonize new environments (e.g. an area with the same temperature and water regime), form new species interactions (e.g. a parasite infecting a new host), or both, which can lead to the misinterpretation of the relationship as coevolution, although the organism has not evolved and is continuing to exploit the same resources it always has.[2][4] The more strict definition of ecological fitting requires that a species encounter an environment or host outside of its original operative environment and obtain realized fitness based on traits developed in previous environments that are now co-opted for a new purpose. This strict form of ecological fitting can also be expressed either as colonization of new habitat or the formation of new species interactions.[2][5]

Origin

The evolutionary ecologist Daniel H. Janzen began to explicate the idea of ecological fitting with a 1980 paper[6] that observed that many instances of ecological interactions were inferred to be the result of coevolution when this was not necessarily the case, and encouraged ecologists to use the term coevolution more strictly. He observed that the existing defense traits of plants were likely produced by co-evolution with herbivores or parasites that no longer co-occurred with the plants, but that these traits were continuing to protect the plants against new attacks.

He expanded this idea in a 1985 paper

heterogeneity of habitats across these ranges, individuals were mostly identical across locations, indicating that little local adaptation had taken place. He described the cyclical life history pattern he believed responsible for this pattern: a species begins as a small population occupying a small area with little genetic variation, but then over the course of a few generations grows to occupy a large area, either because of the emergence of a genotype successful over a wider range, or because of the removal of a geographic barrier. This large interconnected population is now subject to many contradictory selection pressures and thus remains evolutionarily static until a disturbance separates populations, restarting the cycle.[7]

This cyclic life history pattern is dependent on three premises: that the ancestral range of most species is smaller than the ones now occupied, that biological communities have porous borders and are thus subject to invasion, and that species possess robust genotypes that allow them to colonize new habitats without evolution.[7] Thus, many biological communities may be made up of organisms that despite their complex biological interactions have very little evolutionary history with each other.

Contrasting views

Ecological fitting represents a contrasting view to, and

adaptationist explanations of why a phenotype or species might exist in a particular environment, and expressed his concern with what he perceived as an overuse of coevolutionary explanations for current species associations. He stated that it would be difficult to distinguish between coevolution and ecological fitting, leading ecologists to potentially spurious explanations of current species associations.[2][6] It is difficult to determine whether a close relationship is the result of coevolution or of ecological fitting because ecological fitting is a sorting process in which only associations that 'fit', or increase fitness (biology), will be maintained.[9] When trying to determine which process is at work in a particular interaction, species can only come into contact through biotic expansion and ecological fitting, followed by adaptation or coevolution. Thus, both processes are important in shaping interactions and communities.[10][11]

Mechanisms

Ecological fitting can occur by a variety of mechanisms, and can help to explain some ecological phenomena. Resource tracking can help to explain the parasite paradox: that parasites are specialists with narrow environmental ranges, which would encourage host fidelity, yet scientists commonly observe parasite shifts onto novel hosts, both in the

phylogenetic record and in ecological time.[12][13] Ecological fitting can explain the frequency of this phenomenon: similar to the expansion phase of the cyclic life cycle described by Janzen,[7] a species undergoes taxon pulses,[14] usually in a time of ecological disturbance, and expands its range, disperses, and colonizes new areas.[10][11][15] For parasite–host, insect–plant, or plant–pollinator associations, this colonization is facilitated by the organism tracking an ancestral resource, and not tracking a particular species.[13][16] The probability of this is increased when the tracked resource is widespread, or when specialization on a certain resource is a shared trait among distantly related species.[13][17] This resource tracking has been demonstrated for both insect–plant and parasite–host systems in which sister species are capable of surviving on each other's hosts, even if they were never associated in nature.[16]

When operating under the more strict definition of ecological fitting, in which traits must be

exapted for a new purpose, several mechanisms could be operating. Phenotypic plasticity, in which an organism changes phenotype in response to environmental variables, allows for individuals with existing genotypes to obtain fitness in novel conditions without adaptation occurring.[2][17][18] Correlated trait evolution can encourage ecological fitting when direct selection on one trait causes a correlated change in another, potentially creating a phenotype that is pre-adapted to possible future conditions.[2][19][20] Phylogenetic conservatism is the latent retention of genetic changes from past conditions: for instance, historical exposure to a certain host may predispose it to colonization in the future.[2][9][15][17] Finally, fixed traits such as body size may lead to entirely different biotic interactions in different environments; for example, pollinators visiting different sets of flowers.[17][21]

Examples

Studies of introduced species can provide some of the best evidence for ecological fitting,

primates[25] or in trout.[26] Another study examined the time required for sugarcane, Saccharum officinarum, to accumulate diverse arthropod pest communities. It determined that time did not influence pest species richness, indicating that host–parasite associations were forming in ecological, not evolutionary, time.[27]

The human-made cloud forest on Green Mountain, Ascension Island, represents an example of how unrelated and unassociated plant species can form a functioning ecosystem without a shared evolutionary history.[28] 19th-century accounts of the island, including that of Charles Darwin on his expedition aboard the Beagle, described the rocky island as destitute and bare.[28] Plants were brought to the island by colonists, but the most important change occurred in 1843 with the terraforming of Green Mountain by botanist Joseph Dalton Hooker, who recommended planting trees on Green Mountain and vegetation on the slopes to encourage deeper soils.[28] Plants were regularly sent from England until, in the 1920s, the mountain was green and verdant, and could be described as a functioning cloud forest.[28] Although some of the species likely were introduced together because of their coevolutionary relationships,[29] the overwhelming mechanism governing relationships is clearly ecological fitting.[30] The system has changed dramatically and even provides ecosystem services such as carbon sequestration, all as a result of ecological fitting.[28][30] This is important with regard to climate change for two reasons: species ranges may be shifting dramatically, and ecological fitting is an important mechanism for the construction of communities over ecological time,[12][22] and it shows that human-made systems could be integral in the mitigation of climate change.[28]

Theoretical applications

Explaining diversity patterns

Ecological fitting can influence species diversity either by promoting diversification through genetic drift, or by maintaining evolutionary

ecospace, plant clades can undergo evolutionary radiation, in which diversification of the clade occurs quickly due to adaptive change.[8] The herbivorous insects may eventually succeed in adapting to the plants' defenses, and would also be capable of diversifying, in the absence of competition by other herbivorous insects.[10] Thus, species associations can lead to rapid diversification of both lineages and contribute to overall community diversity.[23]

Ecological fitting can also maintain populations in stasis, influencing diversity by limiting it. If populations are well-connected through gene flow, local adaptation may not be able to occur (known as antagonistic gene flow), or the well-connected population could evolve as a whole without speciation occurring. The Geographic Mosaic of Coevolution theory can help to explain this: it suggests that coevolution or speciation of a species occurs across a wide geographic scale, rather than at the level of populations, so that populations experiencing selection for a particular trait affect gene frequencies across the geographic region due to gene flow. Populations of a species interact with different species in different parts of its range, so populations may be experiencing a small sub-set of the interactions to which the species as a whole is adapted.[12][32][33] This is based on three premises: there is an environmental and biotic interaction mosaic affecting fitness in different areas, there are certain areas where species are more coevolved than others, and that there is mixing of allele frequencies and traits between the regions to produce more homogeneous populations.[32][33] Thus, depending on connectivity of populations and strength of selection pressure in different arenas, a widespread population can coevolve with another species, or individual populations can specialize, potentially resulting in diversification.[17]

Community assembly

Ecological fitting can explain aspects of species associations and community assembly, as well as invasion ecology.

Henry Gleason, who was also a plant ecologist studying successional communities, is more individualistic and emphasizes the role of random processes such as dispersal in community assembly.[35] The Clementsian view would emphasize coevolution and strict niche fidelity as a major factor structuring communities, also known as the niche-assembly perspective, whereas the Gleasonian, or dispersal assembly view emphasizes neutral and historical processes, including ecological fitting.[28][36] These views of community assembly prompt questions, such as whether species continue stable relationships over time, or if all individuals represent "asymmetrical pegs in square holes".[7][36] Some of these questions can be answered through phylogenetic studies, which can determine when certain traits arose, and thus whether species interactions and community assembly occurs primarily through coevolution or through dispersal and ecological fitting. Support exists for each, indicating that each has a varied role to play, depending on the community and on historical factors.[36]

Emerging infectious diseases

A field of recent[

leopard frogs, even though bullfrogs do not and have never occurred in this area.[38] When an emerging infectious disease is the result of ecological fitting and host specificity is loose, then recurrent host shifts are likely to occur and the difficult task of building a predictive framework for management is necessary.[12]

Related terms

References

  1. S2CID 84910076
    .
  2. ^
    PMID 18778274
    .
  3. doi:10.1101/sqb.1957.022.01.039. Archived from the original
    (PDF) on 2007-09-26. Retrieved 2011-01-30.
  4. S2CID 205432131
    .
  5. ^
    JSTOR 1368525
    .
  6. ^
    S2CID 14608571
    .
  7. ^
    JSTOR 3565565
    .
  8. ^
    JSTOR 2406212
    .
  9. ^
    ISSN 0030-1299
    .
  10. ^ a b c Janz, N.; Nylin, S. & Tilmon, K. J. (ed.) (2008). "Chapter 15: The oscillation hypothesis of host plant-range and speciation". Specialization, Speciation, and Radiation: the Evolutionary Biology of Herbivorous Insects. University of California Press, Berkeley, California. pp. 203–215. {{cite book}}: |first3= has generic name (help)
  11. ^
    doi:10.3354/meps311251
    .
  12. ^
    doi:10.1590/s1984-46702010000200001
    .
  13. ^
    PMID 16922304.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  14. ^ Erwin, T.L.; Nelson, G. (ed.) & Rosen, D.E. (ed.) (1981). "Taxon pulses, vicariance, and dispersal: an evolutionary synthesis illustrated by carabid beetles". Vicariance biogeography: a critique. Columbia University Press, New York. pp. 159–196. {{cite book}}: |first2= has generic name (help)
  15. ^
    ISBN 978-0-19-956135-3. {{cite book}}: |first3= has generic name (help
    )
  16. ^
    S2CID 28565232
    .
  17. ^
    doi:10.1034/j.1600-0706.2000.880222.x
    .
  18. ISBN 978-0-19-512235-0
    .
  19. S2CID 36544045
    .
  20. PMID 12482948.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  21. JSTOR 3545623
    .
  22. ^
    PMID 17640765
    .
  23. ^
    S2CID 84647531
    .
  24. JSTOR 2097225
    .
  25. S2CID 82689429
    .
  26. ^
    S2CID 32761353
    .
  27. JSTOR 1935118
    .
  28. ^
    S2CID 59332510
    .
  29. doi:10.1111/j.1365-2699.2004.01118.x
    .
  30. ^
    doi:10.1111/j.1365-2699.2004.01216.x
    .
  31. ^ a b c Brooks, Daniel R. (2002). "Taking Evolutionary Transitions Seriously". Semiotics, Evolution, Energy, and Development. 2 (1): 6–24.
  32. ^
    ISBN 978-0-226-79762-5
    .
  33. ^
    S2CID 11656923
    .
  34. ISBN 978-1-162-21647-8
    .
  35. JSTOR 2479596
    .
  36. ^
    PMID 19473217
    .
  37. S2CID 26853701
    .
  38. ^ a b Brooks, Daniel R., Deborah A. McLennan, Virginia León-Règagnon, and Eric Hoberg (2006). "Phylogeny, ecological fitting and lung flukes: helping solve the problem of emerging infectious diseases". Revista Mexicana de Biodiversidad. 77: 225–233.{{cite journal}}: CS1 maint: multiple names: authors list (link)

External links

  • [1], Fasting-growing man-made rainforest may change leading ecological theory, Mongabay
  • [2] Ascension Island: Another Green World, The Economist
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