'Big headed' ant, Pheidole megacephala (soldier cast).
As well as species evolving, there is another form of biological evolution that is often not recognised as such - the evolution of ecosystems as the populations of species that exist within it changes.
Environmental change is the prerequisite of evolutionary change on the classic Darwinian evolution by natural selection model, so we would expect to see an evolutionary change to significant environmental change, given time, but changes to delicately-balanced ecosystems can occur very quickly - in a matter of years or even months, whereas evolutionary change in the species gene pool will normally take many generations to occur, and that slow response to ecosystem change often results in extinction or sometimes, in favourable conditions, a population boom.
And one such ecosystem change is currently underway in Africa due to a small, invasive species of ant, as Professor Todd Palmer, an ecologist and professor in the Department of Biology at the University of Florida, with colleagues including University of Wyoming doctoral candidate and Kenyan scientist Douglas Kamaru, Jake Goheen, from the University of Wyoming, and Corinna Riginos, with The Nature Conservancy reported recently in Science.
I have remarked several times elsewhere how, because the giraffe's long neck and legs have evolved in an arms race with acacia trees, if acacia trees disappeared what is now an advantage to giraffes, would become a handicap as they find drinking difficult and are vulnerable to predation by lions and leopards as they drink because they can't raise their heads up rapidly without a dangerous fall in blood pressure to their brain and that, together their spread-eagled legs, mean they can't suddenly get up and run. Their long necks and legs only make sense in the presence of acacia trees.
And acacia trees have also been evolving in this expensive -do-or-die arms race with giraffes and other browsing species, in which the massive cost of producing enough sugar to build such a tall trunk would also be a handicap in the absence of giraffes. But, in one of those serendipitous turns of good fortune, acacia trees have an ally in this arms race in the form of vicious ants of the Pseudomyrmex and Crematogaster genera that take up residence in swellings at the base of thorns in the crown of the tree. These ants vigorously defend the trees against not only giraffes, but also elephants which can reach to lower branches with their trunks and will even push them over to get at the leaves.
The close interdependence of acacia trees and these ants is an example of co-evolved mutualism:
Acacia cornigera which is also referred to as a swollen-thorn acacia is found in close association with ants (Pseudomyrmex ferruginea). Janzen (1966) undertook an extensive study of the interaction between these two species in their natural habitats of Central America. The acacia provides a home and food resources for the ants. The ants provide the acacias with protection from both insect herbivores and plant competitors.In Africa about 11 species of acacia are associated with around 20 species of ant of the Crematogaster genus.
The ants hollow out the large thorns of the acacia and use them as protective structures and a place for raising their young. The acacia also provides the ants food from their enlarged foliar nectaries. Acacias also produce small protein rich buds at the tip of their leaves called Beltian bodies which are an additional source of food for the ants. Virtually all the food used by the ant population comes from the combination of acacia nectar and Beltian bodies. Many acacias will shed their leaves during the dry seasons to conserve moisture. The swollen-thorn acacias provide nearly year-round leaf production to accommodate the ant population.
The ants are aggressive and will attack other insects and small mammals that attempt to forage on the acacia. Likewise, neighboring plants that start to encroach on the acacia or the space close (within 10–150 cm) to the acacia are trimmed down by the ants. This reduces the competition for growth and allows the acacias to increase in size more rapidly, which then also provides the ants with greater resources.
Janzen (1966) notes that one of the advantages of this system for studying a mutualism is that the ants can be experimentally removed from the acacias to observe the impact that a lack of ants has on plant growth and survival. Janzen in fact predicts that the acacia population would probably go extinct if the local ant population were completely removed.
Laurence Mueller, in Conceptual Breakthroughs in Evolutionary Ecology, 2020
And acacia trees also provide cover for lions as they stalk a major prey species, zebras.
So, a whole interdependent, dynamic ecosystem has evolved over the years in which elephants, giraffes and other species are deterred from over-grazing the acacia trees, and lions have enough cover to hunt their preferred diet - all hinging on the vicious ants living in the acacia trees.
But, and here is where the big change is occurring, those ants are now a major prey species of a small invasive, 'big-headed' ant, Pheidole megacephala that is a voracious predator on other insects. This has now diminished the acacia ant population so much that elephants in particular are no longer deterred from eating acacia trees and acacia trees are quickly disappearing. The first losers in this change, apart from the acacia ants and the acacia trees, is the lions who can no longer successfully ambush zebra, so they have turned their attention to buffalo, which, while more dangerous for the lions to hunt, are slower and easier to ambush.
So, the introduction of this tiny ant, which is spreading throughout the tropics, is threatening the extinction of the acacia ants, acacia trees, lions and buffalos and reducing predation on zebra and if acacia trees go, they'll be followed quite quickly by the now-handicapped giraffe.
AbstractEcological evolution exactly parallels species evolution with the species in the system being analogous to the genes in a species, as the ratio of different species changes so the ecosystem changes.
Mutualisms often define ecosystems, but they are susceptible to human activities. Combining experiments, animal tracking, and mortality investigations, we show that the invasive big-headed ant (Pheidole megacephala) makes lions (Panthera leo) less effective at killing their primary prey, plains zebra (Equus quagga). Big-headed ants disrupted the mutualism between native ants (Crematogaster spp.) and the dominant whistling-thorn tree (Vachellia drepanolobium), rendering trees vulnerable to elephant (Loxodonta africana) browsing and resulting in landscapes with higher visibility. Although zebra kills were significantly less likely to occur in higher-visibility, invaded areas, lion numbers did not decline since the onset of the invasion, likely because of prey-switching to African buffalo (Syncerus caffer). We show that by controlling biophysical structure across landscapes, a tiny invader reconfigured predator-prey dynamics among iconic species.
Douglas N. Kamaru et al. ,
Disruption of an ant-plant mutualism shapes interactions between lions and their primary prey. Science 383, 433-438 (2024). DOI:10.1126/science.adg1464
© 2024 The Authors, Published by American Association for the Advancement of Science.
Reprinted with kind permission under license #5717000308213.
ID is not a problem for science; rather science is a problem for ID. This book shows why. It exposes the fallacy of Intelligent Design by showing that, when examined in detail, biological systems are anything but intelligently designed. They show no signs of a plan and are quite ludicrously complex for whatever can be described as a purpose. The Intelligent Design movement relies on almost total ignorance of biological science and seemingly limitless credulity in its target marks. Its only real appeal appears to be to those who find science too difficult or too much trouble to learn yet want their opinions to be regarded as at least as important as those of scientists and experts in their fields.
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