Interspecific Aggressive Responses • Competition for food • This occurs when resources become scarce. • It leads to stress and a reduction in population size, especially for the least successful species. One population may even become extinct. • Gause’s Principle (competitive exclusion principle) – ‘no 2 species with identical ecological niches can co-exist for long in the same place’.
Interspecific Aggressive Responses • One species will die out, or move away, or the species will differentiate their niches (often subtlety).
Predator-Prey Relationships • Not truly an aggressive relationship. • Predators can limit a population to a healthy level. • Most predators tend to catch the least well-adapted animal, sick or old. • Keeps the gene pool of the prey strong. • The 2 species are dependent on each others well-being.
Variables in Predator-Prey Relationships • The density, size and reproduction rate of the prey animals. • The variation in the predator-prey ratios for different prey species. • The possible differences in what the predator might eat if there was plenty of food , compared to what it actually does eat.
Factors to Consider… • Energy Balance • It will not benefit the animal if it uses up more energy in the hunt than it gets eating the carcass. • Weather • In warm weather, less energy is expended by mammals in keeping warm. • E.g. lions need less food than wolves.
Factors to Consider… • Size • Larger animals tend to eat less food per unit weight than smaller animals • Endurance • Cats, in general, lack the endurance of animals such as wolves. • They stalk their prey very carefully, saving energy for the short, sharp rush. • Wolves always hunt and lions sleep 22hrs a day.
Factors to Consider… • Social Systems • Male lions may expend no energy on the hunt. • These individuals require fewer calories than if they hunted actively. • Size of Prey • If a group of hunters can bring down a large animal and share the carcass, the energy expended would be worthwhile. • Small prey are for individual kills.
Adaptations for Getting Food • There are 3 main ways of feeding: • Staying in one place and letting the food come to you. • Moving about and finding the food. • Parasitising another organism.
Letting the Prey Come to the Predator • Sifting the Environment • Barnacles, mussels, Baleen whales, swifts and some bats • Dangle Bait • Snapping turtle, angler fish. Both these stratergies require good camouflage to work. Video
Letting the Prey Come to the Predator • Webs and Traps • spiders • Lying in Ambush • Praying mantis • video
Moving After the Prey • Having the Right Appendages • Hunting in swarms • Army ants • Hunting in teams • Pelicans, lions, African Wild dogs, Barracuda • Using tools • Sea otters, Chimpanzees, finches
Parasite/ Host Relationships • Parasites, for the most part, exist at the expense of the host. • Parasitoids – parasites with a free living stage in their life cycle
Defence Strategies • Camouflage • Animals can camouflage their smell or the sound that they make. • Visual camouflage is the most commonly used means of defence. • Bulk is usually disguised by countershading. • The silhouette is disguised with disruptive colouration.
Defence Strategies • Camouflage • Camouflaging eyes is most important as this is the head and brain end, a vital part of the animal. • Eyes can disappear amongst stripes and blotches, and some animals flaunt a false eye in a different part of their body.
Defence Strategies • Blend and Bluff • Certain animals, especially those that are nocturnal, rely on camouflage during the day to go unnoticed. • They remain motionless and cryptic colouration protects them.
Defence Strategies • Startle the Predator • A screech owl bluffs by swelling, and flapping its wings. • Many moths have eye patterns on their wings, which they flash. • Many caterpillars have eye spots painted on their bodies • The caterpillar makes the appropriate part of the body appear thicker, to look like a head.
Defence Strategies • Pretend to be Inedible • Many animals gain protection by imitating both the physical structure and behaviour of objects regarded as inedible by the predator. • A caterpillar or a stick insect looks like a stick and freezes motionless • Tropical katydids look like leaves, complete with veins and blemishes • A tropical frog sits on leaves and is coloured to look like bird dropping • Moths look like tree bark • Angler fish and turtles look like rocks
Defence Strategies • Mimicry • An organism’s close imitation of the appearance of another organism to which it is not related. • Batesian Mimicry • This is the resemblance of a harmless or palatable species to one that is dangerous, poisonous or revolting. • E.g. a fly looking like a bee
Mimicry • Mullerian Mimicry • Several poisonous species that all have similar warning colouration, this works to the advantage of all the species. • Yellow and black stripes are a definite warning and many animals use these colours.
Aggressive Mimicry • Amongst cleaner fish. • Wrasse, this fish has white and black stripes running along the body. • They set up cleaning stations in coral reefs. • Fish, recognising their colouration, will queue to be cleaned of parasites. • Another fish called a sabre-toothed blenny that mimics the cleaner fish colouration.
Aggressive Mimicry • As the trusting fish approach them, they take a quick bite out of a fin or tail.
Warning Colouration – Aposematic Colouration • Many animals warn that they are dangerous by having bright colours, especially stripes • E.g. monarch butterflies, wasps, striped snakes.
Warning Sounds – aposematic sound • Bats hunt at night using ultrasonic squeaks. • Some prey moths give out ultrasonic clicks when they hear the bat’s squeaks. • The bats never eatthese moths.
Firing Chemicals • Snakes spit venom. • Skunks spray nasty smells. • The bombardier beetle fires a revolting chemical in the face of a would be attacker.
Curling up • Armadillo, porcupines, hedgehog and slaters all roll up into a ball when attacked. • These animals are usually covered with tough scales or sharp spines that the predator can not penetrate.
Retreating Into a Shell • Snails pull into their shells, blowing bubbles of a nasty green chemical as they do so. • Clams, pipi and toheroa clam up. • Turtles and tortoises can pull their legs and heads into their shells for protection.
Keeping Watch • Many animals sniff the air and keep a wary eye while they eat. • In groups some animals are the ‘lookouts’, allowing others to eat in peace. • In mixed groups of animals, the cries of warning by one species will be heeded by others.
Hiding • Animals will dive into the mud, sand, snow or anything that will ‘give’ enough to hide a body; then, a quick flick with a flipper, fin or leg covers the back. • E.g. flounder
Playing Dead • Many predators are geared to only attack live prey, and leave anything that looks dead alone. • European grass snake turns upside-down with its mouth open wide and keeps totally still. It also secretes a chemical that attracts blowflies. • American oppossums.
Escape by Numbers • Offering a predator so many food items at once that it can’t eat them all. • Shoaling fish
Interspecific Co-operative Behaviour • Mutualism • Both animals benefit • Commensalism • One animal benefits, and the other is not harmed of benefitted