Interspecific aggressive responses Year 13. Competition between animals is usually for: 1)Food 2)Water 3)Space 4)Breeding sites If the competition is

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  • Interspecific aggressive responsesYear 13

  • Competition between animals is usually for:FoodWaterSpaceBreeding sites

    If the competition is intense, one population may become extinct.

  • Predator-prey relationshipsMost predators tend to catch weak, sick or old animals. This way the gene pool of the prey population is kept strong.

    In a predator-prey relationship, the two species are dependent on each others well-being. A predator that eats too many prey will cut off its own food source. The predators also regulate the size of the prey population.

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  • In any predator-prey graph, the prey always has a higher population and precedes the predator.

  • Adaptations for getting foodThere are 3 ways of getting food:Stay in one spot and let the food come to youMove and find foodParasitise another organism.

  • 1. Letting the prey come to the predatorBaleen whales swim through the sea, trapping their food on baleen sieves.A. Sifting the environment

  • Barnacles open their trapdoors and wave hairy feet about in the water to trap plankton.

  • B. Dangle baitAngler fish has a glowing appendage on the top of its head that it dangles to attract prey.


  • The snapping turtle has a worm-like structure on its tongue. It waits with its mouth open, wriggling the worm. Fish go to eat the worm, the turtle snaps its mouth shut, catching the fish.

  • C. Webs and trapsWebs: Web spiders spin strong sticky threads to trap flying insects.Trapdoor spiders dig holes in the soil, and cover them with a trapdoor. If an animal comes near, spider shoots out and pulls prey into hole.

  • D. Lying in ambushMany animals lie in ambush to get their prey, using camouflage and stealth rather than speed.Example praying mantis. Sits motionless until prey comes by. It then lunges and grabs prey between two front legs.

  • 2. Move and find food

  • B. Having the right appendagesMany animals have special appendages in order to eat their food.Snakes can disengage their lower jaw in order to swallow an egg.Teeth are often specialised depending on the food source. Eg meat eaters have incisors.

  • 3. Different birds have different beaks which are adaptations related to their food source.Woodpeckers can chisel a hole to get at beetle grubs.Other birds have small beaks for picking up fine seeds.

  • C. Hunting in swarmsArmy ants hunt in a group (750 000) and overcome opposition with their bites and sheer numbers.Army ants swarm on a scorpion.

  • D. Hunting in teamsLions, hyenas and wolves hunt in packs with coordinated team work.

  • Barracuda drive fish into shallow water where they are easier to catch.

  • E. Using toolsE. Tool use: Chimpanzees use twigs or grass stalks to extract termites from their holes.

  • 3. Parasite/ host relationshipsParasites live in or on a host organism. The host is always harmed by the presence of the parasite, but it is not usually killed.Tick ectoparasite on a bird wing

  • Head louse -ectoparasiteTape worm from puppy - endoparasite

  • *Social Parasites e.g. cuckoo - a brood parasite. e.g. ants slave-making of other ants nests.The picture shows a queen of a social parasite, Acromyrmex insinuator, being harassed by a worker of its host species, Acromyrmex echinatior. Socially parasitic ants use the nests and workforce of other ant species to raise their own offspring. The queens of social parasites need to get inside the nests of other ants, where they will lay eggs which are reared by the workers of their host.

  • *


  • Defence strategies against predatorsJust as predators have strategies for locating and capturing prey, prey have counter strategies to avoid being detected, subdued, and eaten.

  • 1. CamouflageCamouflage is used to avoid detection. Adaptations in form, colour, patterning, and behaviour enable prey species to blend into their surroundings.


  • 2. Startle the predatorAn owl can screech and flap its wings, startling a predator.

    Many moths have eye patterns on their wings which they flash. This startles the predator, allowing the moth to escape.

  • Meerkats have lookouts to warn the group against predators.

    Some animals like fawns hide.3. Avoid the PredatorsGroup vigilance and alarms in meerkatsHiding is a common strategy of fawns

  • 4. MimicryMimicry is when an organism looks like another organism to which it is unrelated.

  • In Batesian mimicry, a harmless, palatable species resembles a toxic or dangerous species. Mimics benefit because predators avoid all individuals with a similar appearance.For Batesian mimicry to be effective, the mimic must not significantly outnumber the model. Predators must have a greater chance of encountering the unpalatable species.Batesian MimicryThe dangerous common waspand its harmless Batesian mimic, the wasp beetle

  • In Mllerian mimicry, unpalatable species tend to resemble each other. The mimics present a common image for predators to avoid.Orange and black, or yellow and black are common warning colours in insects. For example, yellow and black stripes are a warning used by bees, snakes and wasps.Mllerian MimicryMonarch butterfly: Danaus plexipusQueen butterfly: Danaus gillipus

  • 5. Warning ColoursMany prey species taste bad, are toxic, or inflict pain on attackers.Truly toxic or noxious species, such as arrow poison frogs and skunks, make little or no attempt to conceal themselves from predators. Instead, they often have warning (aposematic) colouration.The conspicuous patterns and colours advertise their unpalatability to predators.

  • Warning ColoursMonarch butterflyArrow poison frogLionfish

  • *Mllerian mimicry in Dendrobates frogs near Tarapoto, Peru (a - c) The three frogs are all putative members of a single species, Dendrobates imitator. Each of these different morphs is sympatric with a different species in a different geographical region. The species with which each morph is sympatric is shown directly below that morph. From left to right, the species in (d - f ) are: Dendrobates variabilis (Tarapoto), Dendrobates fantasticus (Huallaga Canyon) and `Dendrobates ventrimaculatus (Yurimaguas).

  • Tough outer coverings, such as shells, are common in several taxa. Almost all mollusks have protective shells. The head and muscular foot can be withdrawn into the shell.Turtles and tortoises are characterized by their hard, protective shell, virtually their only defense.6. Body ArmourPill millipedeTortoiseStag beetle

  • 7. Curling upSome animals like the porcupine, armadillo and hedgehogs curl into a ball when attacked. Spines and scales protect the animal from attack.

  • Many insects, including the Bombadier beetle and pentatomid bugs (stink bugs), exude or spray a noxious fluid when attacked.North American skunks can squirt a strongly smelling, nauseous fluid from their anal glands, at would-be attackers.8. Chemical DefenseNorth American skunkPentatomid (stink) bug

  • Individuals within large groups are each less vulnerable to attack than they would be if alone.Large flocks of birds and schools of fish tend to move together as one mass in a way that confuses predators and makes the isolation of individuals difficult.Large groups also provide greater surveillance; a predator is much less likely to approach a large group undetected.9. Group DefenseFlamingoes congregate in large flocksLarge schools confuse predators

  • Morphology and behaviour are shaped by natural selection.Predation provides strong selective pressure on prey populations to evolve effective defense mechanisms, e.g.greater speed and agilitybetter surveillanceIn turn, natural selection favors counter-adaptations in predator populations, cooperationgreater stealthThe Evolutionary Arms RaceSlower, more vulnerable individuals are often those that fall prey to predatorsNatural selection favors the more capable hunters

    *********************Figure 3. Cuckoo parasitism. (a) Adult shining bronze cuckoo (Chrysococcyx lucidus) in western Australia. (b) One-day-old nestling Horsfield's bronze cuckoo (Chrysococcyx basalis) after it has evicted young splendid fairy-wrens (Malurus splendens); note the hollow back that balances the host egg while the nestling evicts it from the nest. (c) Klaas cuckoo (Chrysococcyx klaas) fledgling fed by a Marico sunbird (Nectarinia mariquensis) in Kenya. (d) Horsfield's bronze cuckoo fledgling fed by an adult western thornbill (Acanthiza inornata) in western Australia. ***************


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