Chainbrakes

Chainbrakes are a new riparian ecosystem found across most major landmasses. The biome is defined by the derived chaintree genus Tectocatenus, also known as Riverchain. Members of the chaingrass family have been associated with water since the Muricene, but riverchain is the first to become a riverside ecosystem engineer. The grass begins to grow a few meters away from running water, as it cannot survive its roots being submerged for long periods. Depending on the topography around the stream, chainbrakes may extend several hundred meters into the surrounding landscape, ending when the chaintrees get outcompeted by drier-adapted plants. In some areas, these may be ground-level grasses; chainbrakes serve the role of gallery pseudoforests in grasslands worldwide. They also grow amid forests of all kinds, though in these cases the chaintrees do not stand alone; they can coexist with a wide variety of wetland trees. 

Few other species are specialized to live solely in chainbrakes, but many use them as dispersal corridors. For mid-sized prey animals, the thick stands of tough, semi-woody stems provide cover from large ground predators, who find it difficult to move through the brakes. A genus of pouchwings called Portents (Prophetornis) is not normally found here, but during mast years, when riverchain seeds are so numerous as to satiate all other granivores, portent birds take advantage of the brakes' safety and abundance. Belonging to the arboreal pouchwing tribe Dendrothylacavini, portents are closely related to stashers. Unlike their cousins, portent pairs keep their eggs (which come in clutches of up to a dozen) in their pouches through the entire incubation process. This has two main effects on their lifestyle.

First, portents can travel great distances while incubating their eggs. Under normal circumstances, this is risky business, as the eggs can easily be broken during transit. Thus, parents will restrict themselves to a modest territory where they know little danger is present. However, during riverchain mast years - about one in twenty - the brakes become highways of favorable conditions for portents, and they may travel hundreds of kilometers before food runs out. The result is that portents show up very suddenly in new ecosystems, and their generalist diet allows them to quickly flourish, often at the expense of the previous inhabitants. Downlings in particular, with their tendency to hyper-specialize by food source, have declined sharply across the former lands of Panapterra since portents began spreading about two million years ago.

Second, since eggs are deposited into a warm pouch immediately after being laid, the oldest eggs in a clutch may hatch as far as two weeks earlier than their last-laid siblings. The young are precocial and require only a few days of parental care, so the parents rarely have to worry about more than three or four chicks at a time. If one hatches during a mast-dispersal event, it will only follow its parents for a short time before establishing a territory along the way. This means a single pair of portents can seed several new locations along its journey. Of course, most will fail to survive in unfamiliar lands, but occasionally one will hold its own. With a maximum lifespan of nearly three decades, a portent stranded in a new area can afford to wait many years before more individuals arrive to form a breeding population. The genus derives its common name from the ominous potential of the first individual; if it does not die, it serves as a warning that an ecological turnover is coming soon.

Back in the brakes, one downling holds the line against pouchwing encroachment. This genus is found nowhere else, as it is specialized to eat the seeds of the riverchain plant. The Brakebreaker (Neoconfractogranus) is the last representative of the nutcracker downlings, which were once the dominant granivorous perching birds worldwide. Now, only one remains, though it seems to be doing well for itself. Brakebreakers are found at low densities across Panapterra, Aglirium, and the Northern Isles. Different landmasses and biomes often have their own morphs, but these do not always betray true species boundaries, as interbreeding has occurred many times in this genus. This is a consequence of the ever-shifting geography of chainbrakes; when watersheds change, a single population can suddenly become isolated high up an isolated river. Alternatively, two river systems can suddenly merge, placing long-separated groups in close contact again. Generally speaking, the selective pressures faced by different brakebreaker lineages is similar, so hybrids have neither advantage nor disadvantage. Exceptions include coloration and size, which must be suited to the local climate, so these traits are regionally specific and stable, even with repeated hybridization.

Riverchain itself has over fifty species, and because each one is specialized for the climate, soil, and hydrology of its region, hybrids are much less likely to survive. A few have massive ranges, such as the Slough Riverchain (T. tidalis), a brackish-adapted species that grows by tidal streambanks close to the ocean. Some of these are true freshwater-driven streams that backfill with seawater when the tide rolls in, while others are passive sloughs that simply drain and fill as the water rises and falls. Erosion rates can be extreme, so this riverchain species keeps most of its biomass in its strong root and rhizome system. This slows the erosive process, and when the bank does eventually collapse, energy can be transferred to portions of the rhizome further uphill, from which new shoots can sprout. The stems are short, usually under two meters, because they are easily lost, so the plant puts little energy into each one. 

The largest Tectocatenus species is known as Gallery Riverchain (T. magnus) and can be found beside rivers on the Deltalands of Ailuropia. Because it faces far less competition than forest-growing riverchains, this species can reach as high as six meters, and as such it supports the world's largest density of brakebreakers: around a dozen per square kilometer during a typical year. During mast seasons, which in this species can last as long as seven months, the local brakebreakers can quintuple in population, rearing one chick after another as long as food remains abundant. Even so, the downlings' low reproductive rate means there will still be food available for many other animals, from seed-storing castlebugs to portents to an assortment of small granivorous swattermice.