Earlier this year we learned that humans and dolphins have more in common than we thought, but while they have the ability to um, experience pleasure similar to humans, they’re a little bit (read: a lot) better at coexisting.
The news today isn’t more unsolicited sexual health news from our dolphin pals, but rather the findings from Flinders University scientists that sheds new light on the reasons why two species of dolphins coexist in the northern Australian waters.
Flinders said that Australian snubfin (Orcaella heinsohni) and humpback (Sousa sahulensis) dolphins live in sympatry throughout most of their range. This is primarily in shallow tropical/subtropical coastal waters, those which are less than 30-metres deep, from southern New Guinea across northern Australia.
“A major challenge in ecology and conservation is to understand the means by which species coexist as this is the basis of biodiversity,” said associate professor Guido Parra Vergara.
“If we are to understand the effects of global change on marine mammal biodiversity, and how we can maintain assemblages of coexisting species, we need to understand their patterns of co-occurrence; the biological significance of their interactions, and the mechanisms underlying their coexistence.”
This is known as ecological niche theory. It predicts the coexistence of closely related species is promoted by resource partitioning in space and time. But fully understanding how different species of marine mammals such as dolphins co-exist is particularly challenging due to their size, high mobility, longevity and the fact that they spend most of their time underwater.
Flinders said ecologically, both species are similar.
Each occur in small populations of typically fewer than 150 individuals, show a high degree of overlap in space use, have similar patterns of habitat use and behavioural activities. As a result, they are seen frequently in mixed species groups.
But this is where it gets super scientific: this shows that segregation into exclusive ranges in space and time, and difference in habitat use and behaviour patterns, do not seem to fully explain their coexistence.
So, to compare stable isotope ratios of carbon and nitrogen in their skin, researchers collected skin samples from live Australian snubfin and humpback dolphins along the east coast of Queensland.
“Differences in carbon isotope ratios are passed up the food web to consumers, providing a quantifiable estimate of habitat and resource use. In contrast, nitrogen isotope ratios increase at each trophic level with top predators having higher nitrogen isotope values compared to lower trophic levels,” the uni explained.
The results of the isotope analysis suggest that while both dolphin species feed at similar trophic levels, have substantial dietary overlap and rely on similar basal food resources, there are subtle differences in their habitat use and prey selection that may promote the coexistence of Australian snubfin and humpback dolphins.
In more simple terms, what these two types of dolphins snack on and need out of a safe space to chill differs a little, with snubfin dolphins munching on a wider diversity of prey, while humpback dolphins forage on a wider range of habitats.
“Food diversity and abundance and habitat heterogeneity are key factors promoting the coexistence of these two dolphin species, and pressure from overfishing and pollution that could reduce prey abundance and diversity or deteriorate their habitat quality could affect the future of such dolphin co-existence,” added Vergara.
You can read the research, Isotopic niche overlap between sympatric Australian snubfin and humpback dolphins, in the Ecology and Evolution journal.