Rats are, without a doubt, the dominant species at this time in Apterra’s history. They may not remain that way forever, but they’ll certainly have a good run for many millions of years. Right now, they are in their first of several golden ages. They rule a world quite friendly to them; unlike the kiwis, they were ancestrally quite well-adapted for subsisting on a grass-heavy diet, and their population exploded immediately after they were introduced. Their numbers far surpass both other land vertebrates on Apterra combined. However, they have experienced little change at this point, for they are under minimal selective pressure in this land of plenty.
Despite this, a few interesting forms have appeared. They live across all environments, only slightly differing from their ancestral condition. In the brackish waters of north Abeli, they swim after their prey, while their cousins scale mountains in search of similar quarry. On the plains, they dive into burrows during the brief moments they lie unattended. Everywhere they find themselves, there is at most one species that challenges them. In the early days, the rats had almost always won this fight.
Those days are over now. Apteryx eggs are no longer easy pickings, and the rats have adapted in turn. The simplest solution to this problem is to stop seeking avian prey. As opportunists, rats have an easy route to becoming dedicated herbivores if given the chance. Vast herds of these rats now roam the plains, cutting swathes of grass down to their roots. Not purely plant-eaters, they will still eat an egg or young chick if they find one, but are more likely to pass right over a burrow if they find it well-defended. They do, however, threaten the burrowing kiwis in a different way. By consuming all the cover in an area, they can leave a nest exposed for their more meat-hungry cousins to discover.
There is at this time only one population of rats that is truly exclusively herbivorous. Most of the time, their population numbers only a few hundred. These rats scrape out a meager living on the outskirts of the Loxodian interior desert, consuming the scraggly grasses clinging to life around small oases and pockets of moisture. A few dozen kilometers further inland, and they would find nothing but barren desert, a land that goes years without a drop of rain. This year, the winds changed, and the moment the rats felt the first drops of rain on their backs, they turned towards the vast desert. An instinct in them was triggered by the arrival of the irregular storm, one honed over the thousands of generations that have already passed since they first arrived in the region.
Four hundred or so rats dispersed across the sands, passing cautiously across riverbeds that would, in a few days' time, run with waters strong enough to carry them away easily. They had less than a week to make their way as far into the desert as possible, establish a territory, and enter a brief period of torpor. As they dug their temporary dens, rain beat down on the sands above them. Seeds that had lain dormant beneath the surface finally cracked open, revealing the tiny green leaves within. In just days, these sprouts reached a foot in height. Not long after, the rats woke up.
The enormous volume of plant matter that grew during the rainy season was far beyond what these few grazers could consume. They filled their bellies, never going hungry, until another instinct took over. Every pair of rats produced between seven and fifteen young with each litter, and the pups reached maturity under a month later. After a few weeks of rain, four hundred became more than four thousand. Another month passed, and 40,000 rats wandered the lush temporary grassland. Three months later, the rains slowed and the plants stopped growing, leaving the rats’ numbers to briefly stagnate somewhere in the low seven-figure range. Now, the first seeds are beginning to drop from the dying plants, and the rats are finding a new source of food. In two more months, there will be nearly 25 million of them swarming the surface of the desert. In years when the rains last slightly longer, the population may increase several times over again.
The last chapter of the desert rats’ story will be a predictable one. The desert grasses will wither and disappear, and the rats, having depleted their food source, will begin to die off. The seeds that avoid being eaten will use their bodies as fertilizer whenever the rain returns to this land. For now, though, life leaves the desert once again. The few surviving rats make their way into the surrounding scrubland, find isolated patches where plants still grow, and await their next chance to invade the desert.