Functional equivalence (ecology)

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In ecology, functional equivalence (or functional redundancy) is the ecological phenomenon that multiple species representing a variety of taxonomic groups can share similar, if not identical, roles in ecosystem functionality (e.g., nitrogen fixers, algae scrapers, scavengers). [1] This phenomenon can apply to both plant and animal taxa. The idea was originally presented in 2005 by Stephen Hubbell, a plant ecologist at the University of Georgia. This idea has led to a new paradigm for species-level classification – organizing species into groups based on functional similarity rather than morphological or evolutionary history. [2] In the natural world, several examples of functional equivalence among different taxa have emerged analogously.

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Plant-pollinator relationships

One example of functional equivalence is demonstrated in plant-pollinator relationships, whereby a certain plant species may evolve flower morphology that selects for pollination by a host of taxonomically-unrelated species to provide the same function (fruit production following pollination). [3] For example, the herbaceous plant spiny madwort ( Hormathophylla spinosa ) grows flowers that are shaped so that taxonomically unrelated pollinators behave almost identically during pollination. From the plant's perspective, each of these pollinators are functionally equivalent and thus are not subjected to specific selective pressures [3] Variation in the shape and structure of both flower and seed morphology can be a source of selective pressure for animal species to evolve a variety of morphological features, yet also provide the same function to the plant. [4]

Plant-animal seed dispersal mechanisms

Plant-animal interactions in terms of seed dispersal are another example of functional equivalence. Evidence has shown that, over the course of millions of years, most plants have maintained evolutionary trait stability in terms of the size and shape of their fruits. [3] However, the animal species that consume and disperse the seeds within the fruits have evolved physically at a faster rate than the plants they feed off of. In other words, animal species have been changing and evolving more than the plants have been changing their seed and fruit morphology. Functional equivalence of the animal species consuming and dispersing the seeds can account for the ability for these plants to continue to survive without genetic changes to their fruit/seed morphology. [3] As with the Hormathophylla example above, the plant species are not subjected to selective pressures the same way that animals are.

Metabolite production

Another instance is the analogous evolution of plant metabolite production as a response to herbivory. In this case, different plant species have evolved different mechanisms of chemical repellant to herbivores, yet each response provides the same function – resistance to herbivory. [3] In some cases, plants living in completely different environments (geographic separation) and that are not taxonomically related can evolve different metabolites that provide the same function to the plant - protection against herbivory. This is another example of functional equivalency among taxonomically unrelated species. [3]

Symbiotic relationships

Numerous instances of functional equivalence may exist within microbial symbionts and their associated host. Some examples of these include the large diversity of microbes within termite digestive tracts and the human gut microbiome. [5] In these environments, a vast array of taxonomically diverse organisms provide the function of food digestion and cellulose breakdown. These microbial organisms most likely evolved under similar conditions but at different points in time, and they have now been discovered interacting with one another and providing the same function to their host organism. [5]

Functional equivalency and biodiversity

Recently, biologists have used the idea of functional equivalency, sometimes referred to as functional redundancy, to make predictions about how to best manage ecosystems and their microcosms. It is a common misconception that high degrees of taxonomic diversity within an ecosystem will ultimately result in a healthier, highly functional system. [2] For example, an ecological microcosm consisting of 30 species of legume plants (which add fixed nitrogen to the soil) is only fulfilling one ecosystem function (nitrogen fixation) despite being rich taxonomically. On the other hand, an ecosystem containing low taxonomic diversity but high functional diversity may be more sustainable. [6] Recent studies have argued that an ecosystem can maintain optimum health by having each ecosystem functional group represented by many taxonomically unrelated species (functional equivalency). [6] [2] In other words, an ecosystem can potentially be at its highest level of integrity if it is both functionally rich and taxonomically rich.

Skepticism

Some biologists have questioned the importance of the functional equivalence theory. For example, Loreau points out that, in actual testing of functional equivalency, it is hard to draw concise conclusions as to whether or not the theory is sound due to the complexity and oversimplification of the theory itself. For example, many studies testing the effects of species loss and functional redundancy rarely address the ambiguity of whether or not functionality is acting at the individual or population level and the possibility for multiple niche dimensions to be overlapping with one another. [7]

Ultimately, the hypothesis of functional equivalence is one that is well recognized among systems ecologists and evolutionary biologists and is an active area of modern research to determine quantitative examples. However, further research is needed in order to quantify the effects of species loss on ecosystem function in order to provide more evidence to support the hypothesis of functional equivalence.

See also

Related Research Articles

<span class="mw-page-title-main">Herbivore</span> Organism that eats mostly or exclusively plant material

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 mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material.

<span class="mw-page-title-main">Mutualism (biology)</span> Mutually beneficial interaction between species

Mutualism describes the ecological interaction between two or more species where each species has a net benefit. Mutualism is a common type of ecological interaction. Prominent examples include most vascular plants engaged in mutualistic interactions with mycorrhizae, flowering plants being pollinated by animals, vascular plants being dispersed by animals, and corals with zooxanthellae, among many others. Mutualism can be contrasted with interspecific competition, in which each species experiences reduced fitness, and exploitation, or parasitism, in which one species benefits at the expense of the other.

<span class="mw-page-title-main">Biological interaction</span> Effect that organisms have on other organisms

In ecology, a biological interaction is the effect that a pair of organisms living together in a community have on each other. They can be either of the same species, or of different species. These effects may be short-term, or long-term, both often strongly influence the adaptation and evolution of the species involved. Biological interactions range from mutualism, beneficial to both partners, to competition, harmful to both partners. Interactions can be direct when physical contact is established or indirect, through intermediaries such as shared resources, territories, ecological services, metabolic waste, toxins or growth inhibitors. This type of relationship can be shown by net effect based on individual effects on both organisms arising out of relationship.

The diversity of species and genes in ecological communities affects the functioning of these communities. These ecological effects of biodiversity in turn are affected by both climate change through enhanced greenhouse gases, aerosols and loss of land cover, and biological diversity, causing a rapid loss of biodiversity and extinctions of species and local populations. The current rate of extinction is sometimes considered a mass extinction, with current species extinction rates on the order of 100 to 1000 times as high as in the past.

A functional group is merely a set of species, or collection of organisms, that share alike characteristics within a community. Ideally, the lifeforms would perform equivalent tasks based on domain forces, rather than a common ancestor or evolutionary relationship. This could potentially lead to analogous structures that overrule the possibility of homology. More specifically, these beings produce resembling effects to external factors of an inhabiting system. Due to the fact that a majority of these creatures share an ecological niche, it is practical to assume they require similar structures in order to achieve the greatest amount of fitness. This refers to such as the ability to successfully reproduce to create offspring, and furthermore sustain life by avoiding alike predators and sharing meals.

<span class="mw-page-title-main">Functional ecology</span>

Functional ecology is a branch of ecology that focuses on the roles, or functions, that species play in the community or ecosystem in which they occur. In this approach, physiological, anatomical, and life history characteristics of the species are emphasized. The term "function" is used to emphasize certain physiological processes rather than discrete properties, describe an organism's role in a trophic system, or illustrate the effects of natural selective processes on an organism. This sub-discipline of ecology represents the crossroads between ecological patterns and the processes and mechanisms that underlie them. It focuses on traits represented in large number of species and can be measured in two ways – the first being screening, which involves measuring a trait across a number of species, and the second being empiricism, which provides quantitative relationships for the traits measured in screening. Functional ecology often emphasizes an integrative approach, using organism traits and activities to understand community dynamics and ecosystem processes, particularly in response to the rapid global changes occurring in earth's environment.

<span class="mw-page-title-main">Nectar</span> Sugar-rich liquid produced by many flowering plants, that attracts pollinators and insects

Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide herbivore protection. Common nectar-consuming pollinators include mosquitoes, hoverflies, wasps, bees, butterflies and moths, hummingbirds, honeyeaters and bats. Nectar plays a crucial role in the foraging economics and evolution of nectar-eating species; for example, nectar foraging behavior is largely responsible for the divergent evolution of the African honey bee, A. m. scutellata and the western honey bee.

<span class="mw-page-title-main">Plant defense against herbivory</span> Plants defenses against being eaten

Plant defense against herbivory or host-plant resistance (HPR) describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants can sense being touched, and they can use several strategies to defend against damage caused by herbivores. Many plants produce secondary metabolites, known as allelochemicals, that influence the behavior, growth, or survival of herbivores. These chemical defenses can act as repellents or toxins to herbivores or reduce plant digestibility. Another defensive strategy of plants is changing their attractiveness. To prevent overconsumption by large herbivores, plants alter their appearance by changing their size or quality, overall decreasing their consumption rate.

Herbivores are dependent on plants for food, and have coevolved mechanisms to obtain this food despite the evolution of a diverse arsenal of plant defenses against herbivory. Herbivore adaptations to plant defense have been likened to "offensive traits" and consist of those traits that allow for increased feeding and use of a host. Plants, on the other hand, protect their resources for use in growth and reproduction, by limiting the ability of herbivores to eat them. Relationships between herbivores and their host plants often results in reciprocal evolutionary change. When a herbivore eats a plant it selects for plants that can mount a defensive response, whether the response is incorporated biochemically or physically, or induced as a counterattack. In cases where this relationship demonstrates "specificity", and "reciprocity", the species are thought to have coevolved. The escape and radiation mechanisms for coevolution, presents the idea that adaptations in herbivores and their host plants, has been the driving force behind speciation. The coevolution that occurs between plants and herbivores that ultimately results in the speciation of both can be further explained by the Red Queen hypothesis. This hypothesis states that competitive success and failure evolve back and forth through organizational learning. The act of an organism facing competition with another organism ultimately leads to an increase in the organism's performance due to selection. This increase in competitive success then forces the competing organism to increase its performance through selection as well, thus creating an "arms race" between the two species. Herbivores evolve due to plant defenses because plants must increase their competitive performance first due to herbivore competitive success.

<span class="mw-page-title-main">Flower</span> Reproductive structure in flowering plants

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants. The biological function of a flower is to facilitate reproduction, usually by providing a mechanism for the union of sperm with eggs. Flowers may facilitate outcrossing resulting from cross-pollination or allow selfing when self-pollination occurs.

Soil ecology is the study of the interactions among soil organisms, and between biotic and abiotic aspects of the soil environment. It is particularly concerned with the cycling of nutrients, formation and stabilization of the pore structure, the spread and vitality of pathogens, and the biodiversity of this rich biological community.

<span class="mw-page-title-main">Community (ecology)</span> Associated populations of species in a given area

In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological community, or life assemblage. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place or time, for example, "the fish community of Lake Ontario before industrialization".

<span class="mw-page-title-main">Insect ecology</span> The study of how insects interact with the surrounding environment

Insect ecology is the scientific study of how insects, individually or as a community, interact with the surrounding environment or ecosystem.

<span class="mw-page-title-main">Plant ecology</span> The study of effect of the environment on the abundance and distribution of plants

Plant ecology is a subdiscipline of ecology that studies the distribution and abundance of plants, the effects of environmental factors upon the abundance of plants, and the interactions among plants and between plants and other organisms. Examples of these are the distribution of temperate deciduous forests in North America, the effects of drought or flooding upon plant survival, and competition among desert plants for water, or effects of herds of grazing animals upon the composition of grasslands.

<span class="mw-page-title-main">Ecological fitting</span> Biological process

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". It can be understood as a situation in which a species' interactions with its biotic and 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.

Seed dispersal syndromes are morphological characters of seeds correlated to particular seed dispersal agents. Dispersal is the event by which individuals move from the site of their parents to establish in a new area. A seed disperser is the vector by which a seed moves from its parent to the resting place where the individual will establish, for instance an animal. Similar to the term syndrome, a diaspore is a morphological functional unit of a seed for dispersal purposes.

Flowering synchrony is the amount of overlap between flowering periods of plants in their mating season compared to what would be expected to occur randomly under given environmental conditions. A population which is flowering synchronously has more plants flowering at the same time than would be expected to occur randomly. A population which is flowering asynchronously has fewer plants flowering at the same time than would be expected randomly. Flowering synchrony can describe synchrony of flowering periods within a year, across years, and across species in a community. There are fitness benefits and disadvantages to synchronized flowering, and it is a widespread phenomenon across pollination syndromes.

Plant strategies include mechanisms and responses plants use to reproduce, defend, survive, and compete on the landscape. The term “plant strategy” has existed in the literature since at least 1965, however multiple definitions exist. Strategies have been classified as adaptive strategies, reproductive strategies, resource allocation strategies, ecological strategies, and functional trait based strategies, to name a few. While numerous strategies exist, one underlying theme is constant: plants must make trade-offs when responding to their environment. These trade-offs and responses lay the groundwork for classifying the strategies that emerge.

Size-asymmetric competition refers to situations in which larger individuals exploit disproportionately greater amounts of resources when competing with smaller individuals. This type of competition is common among plants but also exists among animals. Size-asymmetric competition usually results from large individuals monopolizing the resource by "pre-emption". i.e. exploiting the resource before smaller individuals are able to obtain it. Size-asymmetric competition has major effects on population structure and diversity within ecological communities.

Herbivores' effects on plant diversity vary across environmental changes. Herbivores could increase plant diversity or decrease plant diversity. Loss of plant diversity due to climate change can also affect herbivore and plant community relationships

References

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  2. 1 2 3 Naeem, Shahid (2006). Foundations of Restoration Ecology. Washington DC: Island Press. pp. 210–237. ISBN   978-1597260176.
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  4. Darwin, Charles (1859). On the Origin of Species. John Murray.
  5. 1 2 Fan, Lu; Reynolds, David; Liu, Michael; Stark, Manuel; Kjelleberg, Staffan; Webster, Nicole S.; Thomas, Torsten (2012-07-03). "Functional equivalence and evolutionary convergence in complex communities of microbial sponge symbionts". Proceedings of the National Academy of Sciences. 109 (27): E1878–E1887. doi: 10.1073/pnas.1203287109 . ISSN   0027-8424. PMC   3390844 . PMID   22699508.
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