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SMALL THINGS MATTER: A SHORT PRIMER ON ANTS IN THE APEIROZOIC WORLD, PART ONE


For hundreds of millions of years, the Earth has been ruled by ants. They have been an important component of most terrestrial ecosystems since they first took advantage of the appearance of flowering plants in the Mesozoic. Today is no different, and despite the constant dangers and setbacks experienced by life on Earth, ants and their Hymenopteran kin have always persisted and overcome all obstacles. Their blossoming diversity and outstanding ability to adapt their environment has allowed them colonise every landmass, barring a few remote islands. We estimate around 50,000 extant species of ants in this time period. Throughout their history ants have developed close relationships with many other kinds of organisms, and this still holds true today. Old alliances and roles remain, and numerous other organisms have seized the opportunity to benefit from the ants' industry. Perhaps even more so than in previous eras, ants are an important part of the daily lives of many organisms including large vertebrates.

Ants are abundant in all regions they are present in except the highest mountains, and are active year-round everywhere except the polar forests. There are
species which are accomplished gliders and swimmers, which we will be able to examine in several locations, but of particular interest are the various habitats we have called 'ant forests', and those species which have developed mutualistic and symbiotic relationships with vertebrates and other post-Holocene Ants have long been accomplished farmers and gardeners, but in this time period we can see this behaviour practiced on an even greater scale. 'Devil's gardens' as they are known in the Holocene, are maintained by numerous species of ant on every continent. These types of antforest are quite striking and easily identified - the forest floor is relatively clear of undergrowth and these small clearings contain only a few plant species. These areas are relatively common, and may cover several thousand square metres. A second type of antforest is less immediately identified, but to the trained eye is just as distinctive as a Devil's garden. In these areas, the ant colony has not just cleared away unwanted plants, but has actively cultivated a new selection of understorey vegetation. These gardens' floral communities are quite distinct and vary between species of ants. Mosaics of these two types of ant garden and uncultivated habitat may cover many acres in favourable areas - usually drier areas, but there are some varzea-dwelling specialists.

A few groups of gardening ants have partially overcome the problem of defending the garden from herbivores by enlisting the help of other organisms in various ways. Strategies range from ignoring certain favoured species of predator, to encouraging them, through to cohabiting with other species such as different ant species, wasps, beetles or termites. One in particular has had a great effect not only on the lifestyles of the ants and their fellow arthropods, but on the evolution of several clades of vertebrate.

You may recall the pair of small Palustrian marsh dergons from this morning - these are derived, endothermic varanid lizards. Varanoids are one of the major clades of vertebrate now present, with many dazzling species and a great variety of form. What probably stood out most about them was their filamentous pelage - quite different to the scales of their lizard ancestors. These structures are known as ribbon scales, and their structure and variety will be covered in a little more depth later on. For now, suffice to say the evolution of the varanid pelage was a major milestone in their evolution. Shortly after their appearance in the late Cenozoic, varanid lizards underwent an incredible radiation in form and expansion in range. Despite the long, hard series of extinctions at the end of the Cenozoic, varanids survived and quickly recovered, once again expanding and diversifying into many fantastic forms. At first glance, even fairly generic ribbon scales appear to be more difficult to maintain than either fur or feathers, and many varanoids look somewhat ungainly and have some trouble grooming themselves thoroughly. It would appear that many of these lizards would bear particularly heavy ectoparasite loads - but this is not often the case. As we will see later, the secret to the success of the varanoid lizards is their long co-evolution with ants.

Anting is a behaviour long known in birds - there is some debate about how or why this behaviour developed in birds, but regardless of its origin the ants' defensive secretions did prove to have some benefits for maintaining plumage. Anting in birds often seemed to benefit the birds significantly more than the ants, and some birds consumed the used, disarmed ants after the ant bath. However, not all birds took to eating their insect benefactors. Over time, some species of ants developed a more mutually beneficial relationship with a lineage of small galliforme birds. Rather than frantically and indiscriminately attacking the bird, the ants discovered a useful source of food in the form of mites, lice and fleas infesting the birds' plumage and leg scales. The birds, in turn, enjoyed an enhanced version of the original anting. Over time, several species of ants specialised in this grooming behaviour. It became a major source of nutrition for a few, and some even sought out birds to groom. Nest-dwelling or -visiting species, and conversely, birds living in ant nests evolved. Birds benefit from the grooming and nest cleaning activities of the ants, and their vigorous defense of their nest. Ants in turn have a useful source of food, and raw materials for farming other organisms in the form of dung and feathers. These are useful for growing fungus. fertilising their garden plants, and farming lice and other keratin eating insects.

Although birds were early adopters of cleaner ants, it was not until ribboned varanids appeared that they really rose to prominence. Varanids were enthusiastic in their uptake of cleaner ant services, and anting behaviour preceded the first real explosion in varanid diversity (concurrent with diversification of cleaner ants of course). Many lizard ants display remarkable complex, host-specific grooming behaviours. No longer limited to simple pest removal, many ants work to maintain the health and structure of the host's skin and pelage. Trimming, smoothing and shaping damaged scales and flaky or irritated skin, removing dirt and providing assistance moulting free varanids from much of the burden of grooming themselves. This has led to cleaner ants becoming valuable resource - burrows and nests with resident ant colonies are sought after and carefully maintained and protected, and territories with independent 'ant stations' are often the most desirable. Many animals, not only varanids, will defend and actively maintain their favoured ant station by chasing away or killing any threats. Anteating animals are not welcome visitors and may be mobbed or attacked on sight even away from ant stations.

While ribboned varanoids have been uniquely dependent on and influenced by cleaner ants for millions of years, after the 'lizard event', bird ants also underwent a renaissance. Birds themselves began developing more and more extravagant and ludicrous display and defensive plumage and body plans, as like the lizards they no longer needed to preen all these structures themselves. No ants are able to properly preen flight feathers or aquatic species' feathers, but do an admirable job off cleaning, tidying and de-lousing the outrageous modified feathers on many of the more unusual lineages of galliform and passerine.

The original bird ants were not dependent on birds for survival, and could function well enough in the absence of an avian lodger. There is one ant lineage that has found an extra use for their resident birds - dispersal. New queens cling on to fledgling or visiting birds with specialised forelimbs, saving them the trouble of growing wings and flying; once the fledgling has alighted in a suitable spot, the queen ant will drop off and go about building a colony. Following the extinction of the mammalian megafauna and the rise of large varanoids, some of these clinging cleaners ants have gone a step further and simply moved into the pelage of their hosts. Flattened bodies and large strong forelimbs enable these strange insects to cling to and forage amongst the varanoid's ribbon plumage. Some allow the ants to colonise them but otherwise leave them to fend for themselves, others will protect their mobile cleaning crew from birds. At the extreme end are the anthouse lizards, which provide a home and some supplemental nutrition in the form of patches of highly modified scales and glandular secretions. In return for their hosts' extra investment, they provide a more aggressive and targeted defense - attacking predators and biting insects. These army cleaner colonies may live permanently on a larger animal, only leaving when the host dies, or they may spend some time living a more conventional life as a nomadic swarm. All types of army cleaner send workers out to forage off-host when the animal is sleeping - the ants' diet and other adaptations are determined by they habits of the animal they live on, so there are a great many host-specific army cleaner.

Birds and varanid lizards are the major benefactors of cleaner ants, but other animals use them too. Amongst mammals, cleaner ant use is limited, but some spiny and scaled species regularly avail themselves. Cervids shedding velvet can be observed visiting ant stations for relief. Interestingly, this is a learned behaviour and only occurs in ant forest and other areas with a high density of independent ant stations. For the most part though, mammals limit themselves to eating ants - possibly because mammal fur is easy to groom and novel structures are less common and elaborate than either feathers or ribbon scales. Gekkotan lizards with modified scales may visit, using the ants to remove shed skin as well as parasites. There is even a cleaner guild which specialises in cleaning other invertebrates. These miniature cleaners remove lice and mites from larger arthropods such as beetles and especially land crabs. An entire suite of mimetic and parasitic organisms has also evolved around the cleaner ants and these are just as fascinating. An assortment of bugs, crabs, beetles, spiders, lepidopterans, termites and molluscs live with and around cleaner ants both on large hosts and in stationary nests.

So to conclude, the reign of ants continues into the Apeirozoic. Their influence can be seen in many of the habitats present and they have shaped the lifestyles and appearance of much of the larger fauna. This time period may lack the towering giants of the Mesozoic and Mid - late Cenozoic, but it is no less interesting and should provide a nice contrast to those eras.

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BTW is the scale toad an actual toad or a lizard?

Monster

Nov 27 2016, 07:12 AM

I saw footage of a sword billed hummingbird preening vs other hummingbirds

Sheather

Nov 27 2016, 04:13 AM

The idea of symbiotic ants is so good I cannot believe nobody has thought of it before! The writing is so well-done descriptively that it doesn't even need illustration. This is my favorite update so far.

HangingThief

Nov 27 2016, 12:03 PM

Sheather

Nov 27 2016, 04:13 AM

The idea of symbiotic ants is so good I cannot believe nobody has thought of it before! The writing is so well-done descriptively that it doesn't even need illustration. This is my favorite update so far.

There are many similar cases of symbiosis between ants and plants.

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I was unaware that there are apparently tours of the future?

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Planet Earth 2 by any chance?

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A few nitpicks-

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It's heartening too, knowing that there are still plenty of original ideas to come up with.

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Geez, either this worlds economy tanked or time travel is ridiculously easy!