Life of the Drylands | Cricket and Finch Symbiosis

North Anciska ~ 15 Million Years PE

The Northern Drylands comprise the largest temperate desert region in the world at this stage, covering an area more than three times the size of California. Two hundred and fifty miles north from the extreme northern edge of the floodplains, they lie at higher elevation and support an entirely different ecosystem. Rain is infrequent here towards the center of the continent, with most falling towards the coasts before ever reaching the region, which grows increasingly desert the further one goes towards the center of the landmass.

North Anciska is a varied continent so far as biomes, progressing from the sprawling wetlands of the central floodplains to widespread tropical forest in the south, temperate savannah to woodland up through tundra in the north, and hot desert in its interior - in addition, of course, to a variety of border habitats in between. It is one of these border habitats we will visit today; intermediate between the sunflower woodlands of southwest Anciska and the dry desert interior crop up innumerable small, patchy savannahs. Though trees grow sparser and smaller the further inland one goes from this point, they continue to occur, albeit in lessening quantities, nearly to the center of the desert, tapping into ground water invisible from the surface and providing a small lifeline that allows complex life to survive even into the extreme depths of the region's hottest heartland.

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Now, here we see a male Robbie's Redbreasted Ground Serin, Terraserinus robertii, a lovely little bird native to the Anciskan drylands - and nowhere else. It is an omnivorous, basal species with a range covering only a few hundred miles in any direction, but within this range it is enormously abundant and it must surely number in the millions, running about the ground, flapping its little under-sized wings as it goes. It's cute, sure, but it's only a few ounces in weight, a tubby and poor-flying species from the same early wave of derivation which by now has mostly died out on the planet, eaten out of existence. Yet this creature persists. It can barely fly and almost never does, and it feeds entirely upon the soil, on insect larvae and large, ripe grass seeds. It lives in an environment surrounded by predators, frequently with no significant cover in which to hide, and beyond its heavy bill it has virtually no defenses of its own against their attacks. How does it survive?

To figure this out, we must delve further into its environment.

Aha! Here it is. Look how lovely it is, early spring in the drylands. Grass is still relatively abundant in this outlying region, including several species of thick-leafed and stocky species which on close inspection far more resemble aloes or yuccas. Alongside miserable, thorny dandelion shrubs, these unusual forms grow low to the ground, sending up colorful, nectar-filled flower stalks even more atypical for their family than their leaves; these are an unusual new offshoot of the grass family which, as a result of Serina's ecological vacuum are beginning to trade their ancestral wind pollination for an insect-driven route, converging closely on showier plants for the same reasons: to attract insects to spread their pollen. These new oddball grasses even fruit, producing succulent fleshy covering upon their seeds for the purpose of feeding birds in the hopes that their actual seeds, hard and fibrous, pass through their tummies untouched and manage to sprout - a real problem for other grasses with such large numbers of seed-eating birds around, to the point where for many others, it is a given few seeds will ever survive, with asexual reproduction through runners and off-shoots providing the main means of reproduction.

Still not far from the dense forests, sunflower trees (many still in winter dormancy, while one early riser has just begun to blossom) still dot the landscape with relative regularity here. Large and weeping, they exist as a strange chimera of parts, resembling trees when in leaf, cacti when in dormancy, and yet when in bloom, showing large yellow flowers effectively unchanged from their ancestors; they are a flower with an identity crisis. Once they all come fully into leaf, they will provide some degree of welcome shade to grazers, such as the large and lithe cursorial aardgoose derivative which has left the wetlands for the upland savannah. She is now carried by long, strong legs and exhibits a bill much better adapted for grazing, with sharp ridges along its length ideal for handling coarse grass - the first of Serina's bird to come to this innovation. She belongs to a new radiation of the aardgoose line which has spread across Anciska, which are adapted to the open grasslands and the food they provide.

But she is not alone in this environment, and there is a reason she now must run - predators have arrived. Though at almost two hundred pounds in weight she worries little from the kestrel-like aerial hunters that are the Falconaries - fully-fledged and capable bird-hunting specialist predators shot off from the shrieker line, now a bane to songbirds everywhere - she has worries of her own. An aberrant offshoot of the formerly herbivorous Axbills of five million years ago has evolved into the much larger and much more fearsome lineage of predators known as Skykes - opportunistic omnivores with sharp bills equally suited to rooting in the soil or killing small prey, such as the now near-precocial, already feathered newborn nestlings and eggs of our poor mother aardgoose, which, hatching at a far more mature stage than their ancestors, would have been able to run after their mother in only three days. Though they could not keep speed with an adult plains aardgoose, the Skykes become one of the earliest megafaunal carnivores in a young Serina. Womblers, those awkward over-inflated remnants of an early predator-free Serina, will decline markedly following the evolution of these large predators and will before long vanish entirely, leaving no descendants.

But below the feet of them all, an enormous lobster-like arthropod shovels soil, expanding its home in search of nutritious roots and tubers out of reach to surface dwellers. This huge creature, which weighs as much as a small kitten - up to two pounds - is in fact a cricket, and by Serinan standards, it is only a medium-sized specimen. With the absence of competition, crickets exploded into subterranean niches very quickly after their introduction to the planet, and unlike many other initially adaptable invertebrates, they've kept their dominion over the underworld even now. However, this particular cricket isn't by himself in this burrow chamber; around him a number of little birds scuttle and scurry, safe within his subterranean tunnels from the dangers of the surface world. They are ground serins, not unlike our fellow above, and while they could never dig out such a nice home for themselves, by making use of their benevolent neighbor's house they are provided shelter unavailable to any other birds. This is their secret to survival.

Why, however, is this neighbor so benevolent? Why should a large burrowing cricket, who has done all of this work to clear out this underground burrow system by itself, tolerate a flock of interlopers setting up house alongside it? It is larger than the serins and easily could trap one against a burrow wall and kill and consume it if it wished, yet it allows them to brush right alongside it without aggression, and it steps lightly over even nutritious nests of eggs which they lay and incubate deep within the burrow system without so much as licking its chops.

This is because here in the drylands, a marvelous example of symbiosis had evolved between the cricket and the finch. The cricket may seem to wear the pants in the relationship, with strength and power, but it is notoriously near-sighted. When it must come to the surface to push soil from its den or to feed when the rains bring nutritious greens to the desert, it could easily be caught and eaten up by some keen-eyed bird waiting just outside. It is so that by allowing a small, non-threatening species of bird to share its home in close quarters, the cricket is provided a highly effective warning system to safeguard itself against attack, in return for allowing the smaller bird a place of residence. As the birds forage for food outside the burrow's edge, they are extremely alert and wary to the slightest danger. If the cricket sees the birds outside foraging, it can be certain that danger is not about and that it, too, can come into the light and feed in safety. If the finch spots danger, it lets out a piercing alarm call and makes a mad dash to the burrow - a call which the cricket too will heed and follow suit, even if it sees no danger itself. When outside the burrow, the cricket never strays further than its comrades, maintaining a position at all times between them and the burrow and frequently keeping physical contact with one of its compatriots at all times, quickly running for cover if it loses this lifeline of safety, at which point a bird will often return to the burrow and lead the cricket back out. In return for the bird's advance notice of danger and protection in the surface world, the cricket gives the otherwise defenseless serin a place to retreat and to rear its young, protected by the large cricket which stations itself near to the burrow entrance, blocking it with its enlarged digging claws when at rest and preventing any other more harmful interlopers from entering the nest.