Figure 3: Identity Test showing niche overlap of the pair are outside
the 95% confidence interval
Discussion
The niche difference has been clearly visible from the study. Four
general factors are opined to be important causes of niche conservatism
which are natural selection, gene flow, pleiotropy, and lack of
variability (Wiens, 2004c; Wiens, 2004a). I believe, the lack of niche
conservatism in this case could have been an interplay of some of these
factors. The new ecological condition in Indus may not have been one
that reduce their fitness or population growth. Otherwise, natural
selection would favour traits that keep individual inside the niche if
there was a cost of reduction of fitness or population growth (Holt and
Gaines, 1992; Holt, 1996). Contemporary genetic exchange has been deemed
unlikely since the populations are separated by several hundred
kilometers of land at their closest point and the dispersal through
brackish water has been deemed highly improbable (Braulik et al. ,
2015). If there was a consideration of the dispersal abilities of
species than it could radically change interpretations of niche
similarity or difference (Peterson, 2011). A clear genetic
differentiation between the two geographically isolated populations have
been found through mtDNA study and there has been speculations that
additional comparative investigations may allow recognition of these
isolated populations as distinct taxa (Braulik et al. , 2015).
Likewise, non-conservatism can be achieved by any change of the three
BAM (biotic, abiotic, movement) factors (Pearman et al. , 2008).
The abiotic conditions includes the climate, physical aspects that
impose physiological limits on species’ ability to persist in an area.
The biotic factors are the set of interactions with other species
modifying the species’ ability to maintain populations. Movement is the
parts which are accessible to the species in some ecological sense. It
is not clear as to the changes in which factors resulted in the
non-conservatism in the present study but movement bears a special
significance by initially separating the species through drainage
capture and then creating of barrier through land and brackish water
limiting their ability to interact.
While generally underutilized, SDM in combination of phylogenetics has
already made contribution on species delimitation (Carstens et
al. , 2013). In a study by Raxworthy et al. (2007) they used
ecological niche modeling for studying species delimitation. The study
elevated three subspecies to species rank using a combination of
morphological, niche study and mitochondrial DNA. The additional
comparative study as suggested by Braulik et al. (2015), should
thus be conducted. An erroneous classification can lead to potentially
inappropriate conservation management decisions for threatened species.
The additional study could help to ascertain the taxonomic status of the
South Asian Dolphins. This is fundamental for insights into the biology
and evolution of species and effective conservation management (Huet al. , 2020). Carstens et al. (2013) recommend that
supposition about species limits should use methods which is an
integration across many data types and analyses. It is rather wise to
fail to delimit species than to falsely delimit entities. The study
clears the air on niche conservatism of the species and it is time to
focus on the genetic evidence of the taxas.
Conclusion
The South Asian Dolphins show very little niche overlap but this article
by no means ascertains the existence of two separate species of South
Asian dolphins. But very little niche overlap were seen and their niches
were not found to be equivalent. A lot of factors have been speculated
on why the niche non-conservatism has been witnessed such as lack of
contemporary genetic exchange. The study simply aids in the discussion
that further efforts are needed to ascertain its taxonomic status.
Correct species delimitation could have a lot of implications for the
conservation of these Endangered taxas. Hence, I recommend further
genetic study to affirm this claim.
Statement of data achieving
The supplementary data and OBIS-SEAMAP
(http://seamap.env.duke.edu/)
provides a complete reference of presence records.
Acknowledgements (optional)
I would like to thank Dr. Dan Warren for entertaining my queries on
ResearchGate regarding the niche equivalency test. I would also like to
thank Mr. Aashish Mishra for reviewing my manuscripts for formatting and
grammatical errors. A special acknowledgement to the Majhi (indigenous
fishing tribe) in Koshi River who’s snatched catch from the protected
area made a deep impact on me to study about Ganges River Dolphins.