Essay on Island Species Richness: Measuring Time-Based Taxonomic Efforts

According to Gray et al. (2014), the authors assert that the Island biogeography approach is a crucial concept in measuring the number of species per island, making taxonomy at its original foundation (Gray et al., 2014). Island biogeography theory requires a metric to be used. Notably, it has been discovered that Island species richness changes with time-based on the taxonomic effort levels, which are a technique used to describe and find the rate of species. An increase or a decrease in the number of species arises from increased sampling or taxonomic revisions to cause a massive impact on the values of single-island endemic species richness (Gravel et al., 2011). In most instances, the single -endemic island species tend to be smaller as compared to island species richness on the same island.

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Species richness is a vital metric applied to validate empirical research and several approaches, especially when the primary focus is to address the reason why specific places have many species as compared to the others (Gray et al., 2014). Taxonomy is the proven scientific foundation that spurs testing, validation, and development of approaches using species richness. In essence, taxonomic is used to defines and specify species based on their distribution, facilitating the performance of regional estimate of species richness to be derived.

The island biogeography approach strives to unify the relationship between species richness, abundance, and island area by generating models such as area curve. Taxonomic efforts comprise two parts, namely, the description effort and sampling effort (Gray et al., 2014). Taxonomic examination sampling effort entails data collation from geo-referenced specimens from specific taxonomic groups to facilitate the assessment of spatial representation collection.

According to Triantis & Sfenthourakis (2012), the authors assert that some island systems there are anomalous characteristics of species richness on the smaller island as compared to larger species (Triantis & Sfenthourakis , 2012). The small island effect refers to the apparent ecological differences between population and faunas of Small Island.

McGlaughlin et al., (2014) argues that the California Channel Island comprises of eight oceanic islands situated at the southern California state, which is closer to the mainland as compared to other wells (McGlaughlin et al., 2014). The island biogeography theory equilibrium states that the diversity of the species on the island will be significantly impacted by the island area. Also, the island species are negatively impacted by isolation.

The equilibrium of theory is realized when there is a balance between extinction and immigration regulated mainly by the island area that has a significant relationship with an environmental degree to a lesser extent (McGlaughlin et al., 2014). Equilibrium theory has been applied over time to other island diversity, such as the correlation between genetic diversity and island area. In essence, genetic diversity is the product of population size and diversity contained in immigrants. Few studies have been conducted to test the relationship between the genetic diversity level and island characteristics, especially for plants (McGlaughlin et al., 2014). Typically, the island population has less genetic diversity as compared with its continental relatives. The correlation between genetic diversity and island area holds for one species in the ADH region, which is not primarily maintained across markers and other species. Ideally, there ceases to be any support for island isolation.

Edwards Wilson and Robert MacArthur were the first people to propose island biogeography theory. In essence, the theory is an equilibrium that depends on the observation where there is an unchanged correlation between the numbers of the species contained in an island and the area of the world's island. In this context, the Island species richness emergences as a balance between the extinction on the island rate and immigration of the species island.

The equilibrium that is obtained as a result is dynamic based on the continuous arrival of the species, which extinct over time (McGlaughlin et al., 2014). If the time is prolonged, the rate of appearance of species and extinction rate diminishes. The theory entails the chiastic dynamic equilibrium, which works at longer time-scales. The theory takes into account the distance and size of the island from the mainland.

An area-effect occurs when there is an increase in island size and biodiversity. If the island is furthest from the island, biodiversity is more likely to become very less, which contributes to the distance effect (Rosindell & Phillimore, 2011). MacArthur-Wilson Model of island biogeography explains the species numbers based on the concept that there is a balance between extinction and immigration rates. In the context of immigration, the theory postulates that the establishment rate of the species already resident the regional species pool size where colonists can come close to the island proximity to colonize resources (Gray et al., 2014). In the context of extinctions, the rates are considered to be slightly low when a small portion of species are resident. However, the extinction rate increases inappropriately when the number of residents increases. The extinction rate is deemed to occur as a result of competitive exclusion, which becomes more pronounced (Gillespie & Baldwin, 2010). When the island is small, and the resident number is high, the population sizes are reduced, making the extinction rate to become higher.

Arguably, the insufficient support for equilibrium approach comprises of two vital aspects. For instance, an expansion in the island area may lead to having many habitat patches per island that can be occupied by the species. However, the equilibrium theory does not relieve the pressure of organisms occurring in a discrete population that may constrain the genetic diversity levels.

The other concept is that the channel island is much closer to the mainland and each other for dispersal to facilitate the augmentation of genetic diversity in many populations through repeated gene flow. Although, there ceases to be any support for the genetic impact predicted by the equilibrium approach (Gray et al., 2014). Some studies support that the most botanically diverse island has several plastid haplotypes, which may lead to successful colonization of events.

According to population genetic theory, the larger the size and number of the population expected on larger islands would contribute to a higher cumulative diversity level on the island (Helmus et al., 2014). In other words, the genetic diversity level should highly correlate with the area of the island. Island communities are usually small, which makes it easier for researchers to study the ecological impacts experienced within the communities.

The theory of island biogeography postulates that the island size and isolation levels from the mainland regulates (S) species richness. In other words, the species number relies on the emigration or extinction of species within the island and the immigration of the new species. In essence, the number of extinction and immigrants depend on the distance between the mainland and the island (Gray et al., 2014). An increase or a decrease in the number of species arises from increased sampling or taxonomic revisions to cause a large impact on values of single-island endemic species richness-extinction rate considered to arise as a result of competitive exclusion, which becomes more pronounced.

References

Frankham, R. (1997). Do island populations have less genetic diversity than mainland populations? Heredity, 78(3), 311-327. https://www.nature.com/hdy/Gillespie, R. G., & Baldwin, B. G. (2010). Island biogeography of remote archipelagoes. The theory of island biogeography revisited, 358-387.

Gravel, D., Massol, F., Canard, E., Mouillot, D., & Mouquet, N. (2011). Trophic theory of island biogeography. Ecology letters, 14(10), 1010-1016.

Gray, A., & Cavers, S. (2014). Island biogeography, the effects of taxonomic effort and the importance of island niche diversity to single-island endemic species. Systematic Biology, 63(1), 55-65. https://doi.org/10.1093/sysbio/syt060

Helmus, M. R., Mahler, D. L., & Losos, J. B. (2014). Island biogeography of the Anthropocene. Nature, 513(7519), 543-546.

McGlaughlin, M. E., Wallace, L. E., Wheeler, G. L., Bresowar, G., Riley, L., Britten, N. R., & Helenurm, K. (2014). Do the island biogeography predictions of MacArthur and Wilson hold when examining genetic diversity on the near mainland California Channel Islands? Examples from endemic Acmispon (Fabaceae). Botanical Journal of the Linnean Society, 174(3), 289-304. https://doi.org/10.1111/boj.12122

Rosindell, J., & Phillimore, A. B. (2011). A unified model of island biogeography sheds light on the zone of radiation. Ecology letters, 14(6), 552-560.

Triantis, K. A., & Sfenthourakis, S. (2012). Island biogeography is not a single-variable discipline: The small island effect debate. Diversity & Distributions, 18(1), 92-96. https://doi.org/10.1111/j.1472-4642.2011.00812.x