Biodiversity: Diversification and Speciation



The Intergovernmental Science Policy Platform on Biodiversity and Ecosystem Service's (IPBES) defines biodiversity as "the variability among living organisms from all sources including, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This includes variation in genetic, phenotypic, phylogenetic, and functional attributes, as well as changes in abundance and distribution over time and space within and among species, biological communities and ecosystems. " (UN Convention on Biological Diversity, 1992).
Biodiversity is essential for the overall functioning of ecosystems as different species cover different roles in servicing the survival of the environment (Gamfeldt 2008). Therefore, the loss of natural biodiversity leads to unhealthy ecosystems more prompt to exacerbating climate-change consequences and thus undermining food security and livelihood of the local communities (UNEP, Facts about the nature crisis). 

But what is the origin of biodiversity and why did speciation occur?

It all started with Darwin, who first theorizes that all species were linked in a single great phylogeny, or tree of life, and that all could be traced back to a presumed single original species. Moreover, species evolved and survived through time by means of natural selection (Darwin 1859). Such discovery allowed us to understand that species adapt and thrive in their specific natural environment and therefore highlighting the importance of the interconnectedness of species and ecosystems.
A key variable in the evolution of biodiversity is geography which leads to speciation by means of geographic isolation (Safran 2012). Geographic isolation will diverge populations from one another by means of natural selection or random chance leading to reproductive isolation, this kind of speciation is called allopatric (Safran 2012). On the other hand, speciation which occurs in overlapping populations not geographically divided is called sympatric (Safran 2012). This might be a result of contrasting patterns of natural selection for adjacent populations which leads to a diversified gene flow in different species (Safran 2012). Finally, parapatric speciation refers to populations which are in close proximity with one another and a small proportion of each are in actual contact (sympatric speciation), whereas all the rest reside far apart from each other, making encounters a rare occasion (Safran 2012).


Recent research aims at finding new modes of speciation. Studies are not focusing anymore solely on geographic variables, but they start to include new evolutionary processes driving genetic divergence (Safran 2012). For example, ecological speciation "is defined as the process by which barriers to gene flow evolve between populations as a result of ecologically-based divergent selection between environments" (Safran 2012). Another current debate is "whether sexual selection can lead to speciation in the absence of ecological divergence" (Safran 2012).  


References:

UN Convention on Biological Diversity, (1992)

UNEP, Facts about the nature crisis, Available at: https://www.unep.org/facts-about-nature-crisis?gclid=Cj0KCQjwgLOiBhC7ARIsAIeetVDxvyw9AKkXFp2qVOtZxz9ypG8CYKOfE0gXP3qZY7DBa0uSdRuO1TEaAldbEALw_wcB

Benton, M.J.,  (2016), Origins of biodiversity, PLOS Biology 14(11)

Lars Gamfeldt, Helmut Hillebrand, Per R. Jonsson, (2008), Multiple Functions Increase the Importance of Biodiversity for Overall Ecosystem Functioning, Ecology 89(5)

Darwin, Charles, (1859), On the origin of species by means of natural selection, or preservation of favoured races in the struggle for life 

Safran, R.J. and P. Nosil, (2012), Speciation: the origin of new species, Nature Education Knowledge 3(10) 

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