Plant Invasions and Invasibility of Plant Communities
Plant invasions are crucial and refer to exotic species’ invasion of a particular ecosystem with or without native plant species. Plant invasions slowly occurred in the past as the earth was minimally explored, and there weren’t enough vectors to carry out the migration of exotic species to new locations (Dimitrakopoulos et al., 2017). The last few centuries have seen an immense improvement in plant invasions. Many exotic species have now invaded new areas, and either thrived alongside the native species or failed altogether (Bellemare et al., 2017). The adaptation of exotic species to an environment is dependent on several factors. These factors include the invading species, the habitats invaded, and how the invasions are managed. The third alternative is the elimination of native species and the progress of the exotic species alone.
Generally, the factors determining species invasiveness can be broadly classified into organism-related factors or ecosystem-centered factors. Organism-related factors include the tens rule, residence time, taxonomic patterns, phenotypic plasticity, and rapid evolutionary change (Jeschke & Heger, 2018). Ecosystem-centered factors include invasion levels, biotic resistance, links between diversity and invisibility, mutualism, and invasion meltdowns. No single factor entirely determines the invasiveness of an exotic species, and therefore there is an interdependence of some of these factors to this phenomenon. The concepts of plant invasion are crucial for several biological processes, including conservation ecology (Jeschke & Heger, 2018). Invasiveness is crucial in helping scientists conserve plant species poised to become extinct by integrating them into a new ecosystem and ensuring their survival. Weed science is another field that is a major beneficiary of plant invasions. This is due to the need for advanced agricultural practices. Identification of species likely to thrive better than weeds in an area is crucial in ensuring the survival of desired plant species.
Biotic Resistance Hypothesis
The biotic resistance hypothesis is also called the diversity resistance hypothesis or the species richness hypothesis. This theory proposes a negative association between original species diversity and ecosystem invasibility. Experimental work shows this true when artificial collections of varying diversity are used in these experiments (Fridley et al., 2007). Contrastingly, observational studies over a huge area show a positive relationship between invasiveness and diversity. The negative findings from observational studies and experimental studies can be explained through several phenomena. On a large scale, the extrinsic conditions that enable the high diversity of native species also support different alien species. These conditions include climate, substrate, and habitat heterogeneity (Petruzzella et al., 2018). The overall positive relationship results from uniting data from many small negative relationships where the extrinsic conditions vary. In a highly diverse community, the utilization of resources is more effective, and productivity is enhanced. The low invisibility of highly diverse communities is due to the low availability of resources hence inadequate supplies for the invading species.
Biotic resistance affects different ecosystems in varying ways, with plants in mesic surroundings being more invasive than those in the terrestrial environment. Rejmánek et al. (2013) explain that the resources aspect of the biotic resistance hypothesis is a major determinant of this phenomenon. Terrestrial environments do not provide sufficient sunlight for the germination and seedling survival of many exotic species. The native plant species in such environments exhibit rapid growth and intense competition for available resources such as sunlight hence difficulty in the survival of exotic species. Functional group identity is a vital factor that has an immense impact on biotic resistance in aquatic environments as only one species survives in these environments, as shown in Figure 1 (Petruzzella et al., 2018).
Note. Adapted from “Mechanisms of invasion resistance of aquatic plant communities” by Petruzzella et al., 2018, Frontiers in Plant Science, 9(134).
Areas with highly diverse native species are likely to be invaded better by exotic species than areas with low species diversity. Fridley et al. (2007) outline the role of other species such as animals in developing biotic resistance as they impact the ecosystem. Some of these creatures, especially aquatic animals, serve as deliberate spreaders of the exotic invaders into an ecosystem.
Plant Communities and Invasions
Plant communities are crucial in influencing invasions into different ecosystems. The plant factors form one side of crucial factors for this phenomenon, with the other side representing ecosystem-centered factors. The invasive species must have features that give it the edge and ensure survival in the foreign ecosystem already occupied by other native species. Some of these factors include fast growth, rapid reproduction, high dispersal ability, phenotype plasticity, environmental tolerance (ecological competence), prior successful invasions, tolerance to a wide range of foods, and association with humans (Hiatt & Flory, 2019). Species that can grow quickly are better capable of invading an ecosystem and thriving as they escape elimination. Species with rapid reproduction ensure that their numbers are always high and favor their continued existence in an ecosystem, such that complete elimination is impossible. High dispersal ability means that a species can spread out over a large area, increasing its chances of survival within the ecosystem that it is invading.
Phenotype plasticity means that a species has the genetic ability to alter itself to suit environmental demands. This ensures that a species is not limited by the hardships that an environment may present (Smith et al., 2020). Aligning itself with environmental demands ensures that a species can invade an ecosystem and appropriately colonize it. Tolerance to varying environmental conditions such as scarce water and sunlight means that a species can survive until the conditions are favorable again (Wang et al., 2020). This encompassed entering a stage of latency and continued thriving when the conditions were appropriate. A plant’s ability to live off different types of food means that it is not dependent on only one food type; hence, it survives when the preferred type is limited. Prior successful invasions are vital for a species as they are crucial markers of their chances of survival in a new environment (Hulme et al., 2017). Association with humans is also vital as they regulate the growth and invasiveness of plants around them. These plants may have developed favorable mechanisms for adaptation.
Plant invasion is an important topic that determines many aspects of life, including food production. The presence of invasion and factors that affect this phenomenon is a reality. The control of these factors for end goals such as weed control is essential and prevents food inadequacy. Manipulation of plant-based factors is possible with advancements in technology and genetic studies. The manipulation of ecosystem-based factors is a possibility and can be done in controlled environments. Ecology has focused on controlling factors such as biotic resistance and finding mechanisms to ensure their interference is favorable. This field is poised to make greater advances in ensuring a better understanding of plant invasiveness and resistance.
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