Predators and prey – everybody’s doing it
Every organism (except those at the top and bottom of the food web) is both predator and prey.
Predators range in size from tiny single-celled amoebae that occur in their billions, to large, less numerous animals such as crocodiles, lions and eagles. Each one has a different strategy to overcome their prey.
The large animals sometimes hunt in packs, or they capture their quarry using cunning, speed and strength.
The smaller organisms use similar strategies or, in the case of the marine cone snail, use a lethal mix of toxins. All predators have important roles in the ecosystem.
Amoebae (including slime moulds) prey on soil-dwelling bacteria, algae, yeasts and other single-celled fungi. They are especially important in controlling populations of bacteria.
The amoebae in turn are eaten by nematodes, another incredibly diverse and species-rich group of organisms.
Nematodes are preyed on by mites, insects and other invertebrates. Mites also predate smaller invertebrates such as springtails (collembola).
There are at least 40 species of carnivorous fungi!
The edible oyster mushroom (Pleurotus ostreatus) preys on nematodes to supplement its nitrogen in nutrient-deficient soils. The fine microscopic fungal threads called hyphae have adhesive strips or lasso-like constricting rings that paralyse nematodes within minutes of contact.
Mites are eaten by other mites, small ladybird-like beetles and other insects. Predatory insects like assassin bugs prey on caterpillars and beetles. Many insects fall victim to spiders that in turn are eaten by birds or wasps.
Small birds fall prey to larger birds including Grey Shrike-thrush, or raptors like hawks and eagles.
Cats, quolls, rats and snakes take a significant number of birds, with one of the craftiest of them all, feral and domestic cats, killing an estimated two billion birds, reptiles and mammals every year.
At the top of the food web are the apex predators. Lions, cheetahs, leopards and bears – amongst others – are native in Europe and the Americas. In Australia we have devils, eagles, quolls and crocodiles.
These animals play crucial roles in the ecosystem by controlling populations of other animals lower in the food web and by preying on weak or sick animals thus keeping the populations healthy.
Their absence and decreasing numbers can have large and unforeseen consequences.
For instance, fewer predators can lead to an increase in herbivorous animals such as pademelons and Bennett’s wallaby.
Left unchecked, large numbers of herbivores can create grazing pressure on native vegetation as well as crops.
This can eliminate food and/or shelter for other animals that live in the understorey, or birds that nest and shelter in dense vegetation.
Top predators are naturally rare, and they are often persecuted because they are perceived as being a threat to livestock. Wedge-tailed Eagles may take the occasional lamb, but this is more than offset by their important role in controlling grazing animals that compete with domestic stock.
All apex predators and their habitats must be protected.
Sarah Lloyd OAM
