Types of inter-specific relationships
These are relationships between members of two different species - it can be two different species of animals, two different species of plants, or the relationship between a species of plant and animal.
Co-operativeBoth species experience increased reproductive success from the relationship
|
CompetitiveNeither species experience increased reproductive success from the relationship, but must stay in the relationship to survive
|
ExploitativeOne species experiences increased reproductive success from the relationship, while the other suffers
|
CommensalOne species experience increased reproductive success from the relationship while the other is neither harmed or helped
|
Animals are classed as being in a mutualistic relationship when the reproductive fitness of both species increase as a result of being part of this relationship. In other words, each species reproduces more successfully because they are in this relationship - if they weren't in this relationship they'd be less successful.
They are more successful because
They are more successful because
- they are more likely to reach the 'reproductive stage' of their life because of this relationship
- they are able to produce more offspring because of this relationship
Zebra and oxpecker example
The oxpecker lands on the zebra and eats ticks and other creepy-crawlies that live on the zebra. In doing so, the oxpecker is getting some delicious food and can just follow the zebra herd around - so is guaranteed a meal! The zebra benefits because it has its own form of pest-control, and is informed of any nearby predators as the oxpeckers fly upwards and start squarking as a warning! This gives it more time to escape any predators!
Both species are more likely to survive and reproduce, increasing their reproductive success as a result of this relationship!
Both species are more likely to survive and reproduce, increasing their reproductive success as a result of this relationship!
Inter-specific competition is when individuals from different species are in direct competition for a particular resource. Each are negatively impacted by the presence of the other. Thus, the reproductive fitness of both species are reduced as a result of being part of this relationship! If they weren't in this relationship, both species would be more reproductively successful! However, particular resources are essential for survival, so both species must compete for it, or die without it!
Lion and hyena example
Lions and hyenas both live in the same environment, are active at the same time and compete for the same food. Because of this, they are in direct competition for essential resources!
Both species are less likely to survive and reproduce, reducing their reproductive success as a result of this relationship!
- For the lion - the presence of the hyena affects the survival and reproductive success of the lion. This is because if the hyena (who often lives in a large pack) obtain a large portion of their shared food resources, the lions will go hungry and be less likely to survive because of this.
- For the hyena - the presence of the lion affects the survival and reproductive success of the hyena. This is because if the lion (and its pride) obtain lots of food, the hyenas will go hungry and be less likely to survive because of this.
- To reduce competition between the species, lions will kill young hyenas. This means the young hyenas won't grow up to reach reproductive age and therefore reduces the reproductive success of the species. Hyenas have been found to kill young lions as well, which has the same effect on the lion population.
Both species are less likely to survive and reproduce, reducing their reproductive success as a result of this relationship!
-
Predation
-
Parasitism
-
Herbivory
<
>
Predator/prey relationships
Over the short-term
The relationship between predator and prey can cause the population numbers of both populations to fluctuate/change i.e. low numbers of prey cause low numbers of predators, high numbers of predators cause low numbers of prey, low numbers of predators can cause high numbers of prey. |
Over the long-term
The relationship between predator and prey can influence the evolution of both species. This is an example of co-evolution - they evolve together. i.e. Prey that have characteristics that help them escape being eaten (e.g. camouflage) will more likely survive and this trait becomes most common in the prey population - same with predators who have characteristics that help them to catch their prey. |
Predator strategies
There are many ways that predators can capture their food!
Letting the prey come:
Letting the prey come:
- Sifting the environment - e.g. Swifts (bird) fly through the sky with an open mouth, insects just happen to fly in
- Dangle some bait - e.g. Angler fish dangle a glowing appendage in front of their face, attracting small fish at the bottom of the ocean. The angler fish then gobbles them up!
- Trap them - e.g. Spiders make a web to catch unwary insects
- Hide, then ambush/attack them - e.g. Chameleons stay undetected by prey, then grab it with its long tongue and eats it up!
- Use their speed - e.g. Cheetah outruns prey then kills them
- Stalk and pounce - e.g. Leopards creep up to their prey (sneakily) then pounce
- Hunt in numbers - e.g. Army ants hunt in huge numbers, all biting and taking down the prey, hyenas hunt in packs
- Paralysis of prey - e.g. Snakes poison their prey, allowing them to then go in for the kill
- Tools - e.g. Thrush birds pick up snails and drop them on rocks to break the shell open
Prey strategies
Prey animals employ some rather incredible strategies to avoid becoming breakfast, lunch or dinner!
Living in groups
Living in groups
- Greater vigilance - e.g. Ostriches live in groups, the more group members, the more likely one of them will detect a predator (more eyes/ears etc. to detect) and they will alert the group, making survival more likely
- Prey dilution - e.g. Antelopes live in large groups - the more antelopes, the less likely you are to be eaten (if you're an antelope!)
- Predator confusion - e.g. Schools of fish group together then split off in different directions, making it hard to focus on a single individual
- Concealment of young - e.g. Wildebeest adults are not preyed on by hyenas, but young are. By keeping young close and concealed, it is harder for predators to spot them
- Camouflage - e.g. Forest Gecko (nocturnal) hides in appropriate background during the day and remains still so predators can't find it
- Batesian mimicry - e.g. Viceroy butterfly mimics the pattern of monarch butterfly . The monarch butterfly is distasteful to the viceroy's predator, so by looking like the monarch, the viceroy is less likely to be preyed upon
- Mullerian mimicry - e.g. Bees, wasps and some snakes all share the same 'warning' colouration, to deter predators - it is easy for a predator to learn what not to eat based on colour
- Diversion of attack - e.g. Emperor Gum Moth has two sets of 'eyes' on its wings, so the predator 'goes' for the wings and not the body, making the individual more likely to survive a predator attack (wings can withstand more damage than abdomen!)
- Autotomy - e.g. Lizards can shed their tail if it is caught by a predator, and it will wriggle around 'alive' and keeping the predator's attention while the lizard escapes
Visualising predator-prey relationships
In order to reproduce successfully, predators must obtain a sufficient amount of food (prey). Without much, predators won't have any/many offspring. There is such a strong relationship between prey numbers are reproductive success of the predator.
As prey numbers increase, so do the predator numbers. This is until there are too many predators, all attacking the prey, causing the prey populations to become very small. This, in turn, affects the number of predators as many don't survive/reproduce due to lack of food/prey. After a while there will be a small number of predators, which will allow prey numbers to grow again as there are less predators attacking them... the cycle continues. |
|
Predators aren't bad - they are actually extremely important for ecosystems to function properly!
|
Parasite/host relationships
This is where one organism lives on/in a host and uses them as a source of shelter and food! The parasite doesn't usually kill the host, but can make it weaker and more susceptible to life-threatening situations. There are two 'types' of parasites:
- Endoparasites
- Ectoparasites
Endoparasites
Parasites that live inside the host. Some endoparasites include tapeworms which live in the gut, liver flukes which live in the bile duct, and roundworms which live inside blood vessels. The reproductive success of endoparasites directly depend on the survival of their host, so it is not in their best interest to kill the host! |
Ectoparasites
Parasites that live on the outside of its host. Examples of these are fleas and mosquitoes. Ectoparasites don't usually have just one host, but can have many, at different times during its life. They are not as imtimately associated with their host, compared to endoparasites! Ectoparasites are what usually spread disease between animals, as they are in contact with the blood of different individuals! |
There's one more type of parasite...
Brood parasites (the most fascinating!)
Brood parasites (the most fascinating!)
|
Some species of animals 'drop off' their young in the home of an animal of another species, so that animal can feed and care for the young rather than its own parents! This means the animal's parents are no longer spending energy looking after their offspring, and can use it to do other things, such as produce more offspring (more offspring = higher reproductive success!). For example, cuckoo birds!
|
Herbivore/plant relationship
Herbivores exploit plants by eating particular parts of the plant - such as the fruit, leaves, seeds or flowers. Herbivores are incredibly important because they kick off the food chain within an ecosystem. They are the primary consumer, the animal that feeds on the producers. Carnivores don't feed on plant matter, they must feed on herbivores!
There are several 'types' of herbivores - they are grouped based on what they eat
- Nectar feeders - they extract the nectar out of flowers by sucking/slurping it out - e.g. Hummingbirds, butterflies
- Pollen feeders - they feed on the pollen - e.g. Honeybees
- Grazers - they feed on grass - e.g. Zebras, horses, sheep
- Browsers - they feed on foilage (shrubs, bushes, trees) (things with leaves) - e.g. Giraffes, goats
- Sap suckers - they feed on the sap from the stems /trunks of plants (they tap into the phloem) - e.g. Aphids
- Chewers - they bite into leaves and roots - e.g. Caterpillars
- Seed and fruit eaters - they eat fruits, nuts, seeds - e.g. Monkeys, squirrels, bats
Herbivores can be generalists (eat all sorts of plans) or specialists (eat only one type of plant). Specialist herbivores are completely dependent on their type of plant for their survival and successful reproduction. Without herbivores, dominant (/best-adapted) plants will overrun particular habitats and 'choke' out other plant species.
Plant defenses
As plants are negatively impacted by herbivores, those that have some sort of trait that allows them to survive and reproduce in the presence of herbivores allows for the evolution of such traits. Below are some examples of plant adaptations that help to protect them from being eaten by herbivores!
As plants are negatively impacted by herbivores, those that have some sort of trait that allows them to survive and reproduce in the presence of herbivores allows for the evolution of such traits. Below are some examples of plant adaptations that help to protect them from being eaten by herbivores!
Mechanical defenses (structural adaptations)
structures used in an attempt to prevent or reduce herbivory
Chemical defenses (physiological adaptations)
toxins or 'bad tastes' used in an attempt to prevent or reduce herbivory
structures used in an attempt to prevent or reduce herbivory
- Spines - leaves that are modified in a way that spikes the herbivore - e.g. Gooseberry, holly (think of Christmas), all types of cactus!
- Thorns - branches that are modified to spike the herbivore - e.g. Hawthorn
- Prickles - parts of the stem that grow outwards, like little thorns - e.g. Blackberry bushes, roses
- Stings - modified hairs that secrete and release chemicals that irritate the skin of herbivores - e.g. Stinging nettle
- Divaricating growth - branches form a big tangled mess (makes it hard for herbivores to eat the plant!) - e.g. Twiggy coprosma
- Hard seeds - seeds enclosed in a hard case - e.g. Macadamia nuts, walnuts
Chemical defenses (physiological adaptations)
toxins or 'bad tastes' used in an attempt to prevent or reduce herbivory
- Cyanogenic glycosides - releases hydrogen cyanide when damage is sustained by the plant - e.g. Clover leaves
- Cardiac glycosides - releases chemical that is classed as a 'heart poison' - e.g. Foxglove
- Insect hormones - plants release hormones that disrupt growth of particular insects and when insects feed on plant they are affected by them - e.g. Ferns and conifers
- Tannins - make plants bitter (distasteful) and harder to digest - e.g. Eucalyptus
- Alkaloids - make plants distasteful and slightly toxic - e.g. Ragwort (toxic to cattle)
Many herbivores still prevail as they can 'overcome' these chemical defenses
- Chemical concentrations in the leaves increase with age, so many herbivores target the young leaves instead
- Different plant species make different types of chemicals - these only have an effect on the herbivore in higher doses, so by feeding on many different types of plants, the concentration of a particular chemical does not get high enough to disturb the herbivore
Sea anemone and clownfish example
Clownfish live amid the tentacles of sea anemones - they are immune to the sting/poisons emitted by the tentacles. They live here as the tentacles offer the clownfish protection from predators, which will be poisoned by the tentacles, yet the anemone remains unaffected by the clownfish's presence!