Pathway · about 15 minutes · 8 steps
The web of partnerships
Read the invisible deals — pollination, seed-planting, dependency — that turn a list of species into an ecosystem.
A species list tells you who is here. It does not tell you who needs whom, and that is the more interesting question.
Start with the New Holland honeyeater working a flower for nectar, then meet the banksia it is paying rent to — a bargain struck in fire and drought. Drop to ground level for the ants that plant wattle seed for a fatty bribe and bury it against the next fire. Then follow a different courier: the mistletoebird, built around one fruit, wiping mistletoe seed onto the very branch that will feed it next. Underground, the trail gets stranger still — an orchid seed that cannot grow without a fungus to find it first, and a bettong that once tilled the hills every night, spreading that fungus as it dug for its dinner.
Eight species, four bargains, one lesson: pull a single thread — lose the ant, the bird, the digging kangaroo — and the whole arrangement can quietly stop working, long before anything visibly dies. Take that with you. Close the page and go outside, and look for the deal being struck on the nearest flower.
- New Holland honeyeater — A sharp, black-and-white, quarrelsome nectar-drinker — one of the region's most persistent flower-workers, and the common, everyday face of a pollination bargain rarer species are losing their grip on.
- Banksia — A hard-leaved shrub that banks its seed in woody cones only a fire will open, and spends the interest on nectar for the region's honeyeaters — the drought-and-fire bargain in one plant.
- The seed-planting ants — Meat ants and their smaller, less conspicuous kin hire out as gardeners for a fatty snack — hauling seed underground, eating the bribe, and leaving the seed itself planted and safe.
- Wattles (Acacia) — A fast, hard-seeded coloniser that pays ants in fat to bury its seed and then leaves fire, not the calendar, to decide when that seed wakes up — a cornerstone of the region's ant-sown flora.
- Mistletoebird — A tiny red-and-black bird that eats almost nothing but mistletoe berries, digests the seed in minutes, and wipes it — deliberately — onto the very branch it is sitting on: a dispersal partnership tuned to exquisite precision.
- Mistletoe — The much-maligned parasite of the gum trees, planted branch by branch by its own dedicated bird — and generous enough, in flower and fruit, to feed and shelter a startling share of the bush's animal life.
- Orchids and their fungi — A native ground orchid's seed is a mote of dust with no food reserve at all — it cannot become a seedling until it is found underground by one particular fungus, which is why you cannot rescue an orchid with seed alone.
- Brush-tailed bettong (woylie) — A rabbit-sized digging kangaroo that once tilled the Adelaide Hills every night, sowing truffle-fungus spores as it went — gone from the whole mainland but for a handful of fenced sanctuaries, one lost gear in the underground loop.
The end-check — put it together
You've walked the steps. Now answer these from what the pathway taught, not from the pages — getting them here is what tells you it stuck.
A dense, untidy ball of foliage hangs from a branch high in an old eucalypt — mistletoe. Its own leaves are green and clearly photosynthesising, yet a haustorium sunk into the branch is drawing on the tree's own water and minerals. What kind of plant does that make it, and what should you do about the loppers?
Mistletoe keeps its own green, photosynthesising leaves and only draws water and dissolved minerals through the haustorium — that half-and-half arrangement is exactly what 'hemiparasite' means, distinct from a true parasite (no photosynthesis of its own), an epiphyte (which takes nothing from its host), or disease. A worldwide review found vertebrates from ninety-seven families feeding on mistletoe and fifty families nesting in its clumps, which is why the old reach for the loppers is the wrong response (Watson 2001).
A rare ground orchid is about to lose its patch of Mount Lofty forest to clearing. Someone suggests collecting its seed and scattering it on suitable-looking soil in a reserve nearby. Why will that alone not save the orchid?
Orchid seed is dust-fine, built for wide wind dispersal, but almost entirely lacking the food store (endosperm) other seeds carry, so it cannot grow unaided (Bonnardeaux 2007). It only becomes a seedling if a compatible mycorrhizal fungus is already present to feed it — a dependency Warcup's germination trials at the Waite Institute showed runs at genus level, greenhoods with *Ceratobasidium* and donkey orchids with *Tulasnella* (Warcup 1971, 1981). Move the seed to soil without its fungus and nothing happens; the transplant or sowing is only ever half the plant. (Ch 15.)
The brush-tailed bettong (woylie) is now extinct across the Adelaide Hills outside a few fenced sanctuaries. Every night of its working life, what underground partnership was it maintaining as it dug through the leaf litter?
Native hypogeous fungi such as Mesophellia and Hysterangium fruit underground and cannot release spores to the wind the way a mushroom does, so they depend entirely on being smelled out, dug up and eaten by mammals like the bettong; the spores pass through its gut and are deposited, still viable, wherever it next digs (Claridge 1994; Danks 2020). Losing the bettong does not stop the loop cleanly, but it removes a fire-tuned, purpose-built disperser from the system at exactly the moment recently burnt ground most needs reseeding.