Resource:
Food/water/shelter/nutrients
Competing (animals)
It is not in the best interest of any competing animal to be at risk of injury, so many animals employ particular behaviours to determine who gains access to particular resources without hurting one another. Social behaviours are more common in groups, rather than solitary animals.
Agonistic behaviour
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Aggressive behaviour
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Agonistic and aggressive behaviour are both used to establish territories and social hierarchies. By employing territories and/or social hierarchies, animals can decide who gets access to resources such as food, water and mates. Not all animals in a population can gain equal access to resources, and the resources might run out!
Resources are needed for an animal to survive and reproduce. The more offspring an animal has (the more genes it can pass on), the more successful the animal is.
Resources are needed for an animal to survive and reproduce. The more offspring an animal has (the more genes it can pass on), the more successful the animal is.
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Territories
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Social hierarchies
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A territory is an area that is defended against other members of the same species. This way of determining access to resources is common in solitary animals (i.e. those who live alone), but is also found in animals that live in groups. Territory holders are guaranteed particular resources since they are strong enough to defend the area. This makes them more likely to survive and reproduce, making them more successful! If in a group, the territory holder (the one who defends the territory) is the one who gains the most resources from within the territory.
Territory - An area that is defended against other members of the same species. It usually contains food and water (but not always), available sites for nesting/mating and is a 'safe' place for the animal. Kind of like our house! It has everything we need and it is where we are safe.
Home range - Surrounds the territory and is not defended. The home range is usually where the animal forages for food. |
A territory is usually marked so that other members of the same species know it is a place that is 'already occupied'. The way a territory is marked can be any of the following:
By marking boundaries, accidental intrusion is likely prevented, thus competition reduced. The only time an animal is likely to 'take over' the territory of another animal is if they have a chance at dislodging the owner. For example, if the owner is old, sick, weak or already deceased.
- noises/vocalisations - e.g. birds singing songs
- scent marking - e.g. dogs and wolves
- visual displays - e.g. pukekos
By marking boundaries, accidental intrusion is likely prevented, thus competition reduced. The only time an animal is likely to 'take over' the territory of another animal is if they have a chance at dislodging the owner. For example, if the owner is old, sick, weak or already deceased.
Costs of territory defence |
Benefits of territory defence |
It is energy expensive: A lot of energy is spent actively defending the territory, as well as marking the territory. |
It saves energy: Instead of always leaving the area to find food, food is close by and possibly defended from others, meaning less time is spent actually foraging for food. |
It is time expensive: A lot of time is also spent defending and marking a territory - this time could be used for doing something more productive, such as feeding or mating. |
It saves time: Again, less time is spent foraging for food and can be spent defending the territory and using the resources that are being defended. |
For species that hold territories - the benefits must obviously outweigh the costs. If resources are extremely limited, often territories are abandoned because: a) If you don't have resources - why defend something that you don't have? b) If you are lucky enough to have resources - when resources are scarce, competition is much more intense and you're more likely to be injured by other animals desperate for resources |
Animals that live in groups often have some sort of social organization in order to 'keep the peace' and share the resources around. However, many groups do not share resources fairly, as there may not be enough to go around. Dominant animals within a group often hold a higher 'rank' and therefore consistently have access to higher quality, or more, resources compared to those who hold a low rank. The most common form of social dominance is a 'pecking order', where an alpha (top) individual dominates over other group members, the beta (just lower than top) dominates over all other group members except the top, etc.
Instead of constantly fighting for resources, many animals share resources and live as a group - in doing so, individuals are guaranteed safety and resources. However within a group, some members gain access to more (or better) resources than others, as they have a higher rank. The individuals with the highest rank are the 'strongest', as they likely fought to be there. Within a hierarchy, there is very little conflict - agonistic and aggressive behaviour keep group members 'in line'. It is better to be at the bottom of the pecking order and get a little amount of resources, than to be out on your own and searching (and possibly fighting) for resources every day. |
Those with a higher rank within the hierarchy gain more food and better access to mates - allowing them to pass on their genes compared to those with a lower rank. Those lower in the ranks have little access to mates, therefore are not very reproductively successful.
Hierarchies are established by physical conflict, but maintained by agonistic behaviours. Some examples of social hierarchies are below!
Hierarchies are established by physical conflict, but maintained by agonistic behaviours. Some examples of social hierarchies are below!
Silvereyes are solitary birds during breeding season, males hold territories which females go to in order to breed. However in winter these birds form flocks and employ a male social hierarchy and a female hierarchy too.
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Hyenas are territorial animals and live in packs of up to 90. In the social hierarchy, females are dominant over males. Female domination is so prevalent that even the lowest ranking female is dominant to the highest ranking male.
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Male dragonet fish form dominance hierarchies, particularly during the time they breed. They act extremely aggressively towards other dragonets to establish mating rights, biting each other and twisting their bodies around one another. Males of this species often suffer higher mortality rates during breeding season as a result of this aggression.
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Competing (plants)
Plants compete with members of the same species for nutrients/minerals, light and water.
- It affects how much growth each individual plant can undergo
- It creates variation in the growth of individual plants within a population
When a group of seeds are planted, some will germinate faster than others. The knock-on effect of this is:
Rapid growth is an adaptive advantage
- Those who germinate earlier will emerge above the soil first they will have no competitors for light, allowing for rapid growth
- Those who germinate slightly later will emerge above the soil and have limited access to light. This is because those who germinated first will be dominating the space and thus soaking up all the light
- Those who germinated slightly later, as a result of limited light, will grow slower. The slower they grow, the less light they will get as those above them have more light
- more light = more PS = more glucose = more respiration = more ATP (energy) = more growth
Rapid growth is an adaptive advantage
- weeds - growing rapidly means they can take over gardens quickly and exploit all available resources
- emerging from dormancy - growing rapidly means that the seedlings will emerge quickly and begin growing as fast as possible, less likely for them to be in the shade of another plant
Co-operating (animals)
Many animals that live in groups will help locate food for the group members to collect, or bring food to those who can't fetch it themselves.
Social insects
Such insects include: honeybees, wasps, termites and ants. They have a very advanced type of group formation!
The social behaviour of honeybees is an innate behaviour (genetically programmed), controlled largely by pheromones. They live in a hive and are grouped based on the division of labour that they do. There is one queen bee, who mates with all the 'drones' and lays all the eggs. The drones live only to fertilise the queen, and die soon after. Worker bees go and find food for the colony, or a new nest, and let other bees know where to find them - using the round and waggle dance! These colonies demonstrate altruism. This is a self-sacrificing behaviour that occurs for 'the good of the colony'. In this case, worker bees sacrifice their own reproductive success so that the queen and several drones are able to reproduce. Altruism is a naturally selected-for behaviour. |
Social mammals
Such mammals include humans, elephants, chimpanzees, meercats, etc. Living in groups enhances the survival of individual in that group.
In such groups, a social hierarchy is often how order within the group is maintained, as well as who accesses resources. The social behaviour of Japanese macaques has been studied extensively. Their social groups contain 50-150 members and have several males at the top of a dominance hierarchy within the group. The alpha macaque male (leader of the entire group) gets his position long after he is a mature adult, based on the social position of his mother - not how 'big' and 'tough' he is. In such group, many young learn behaviours by watching other group members. Behaviors such as washing sand off potatoes - it's not an innate behaviour, it is learned. Such behaviour can only really be passed down in groups, not in animals that live solitary lives. This is called cultural evolution. |
Resource:
mates
competing
The 'goal' for all living things is to pass on their genes. The more genes you can pass on, the more successful you are as an animal. This leads many animals to compete for mates, as this directly affects their success! Males and females both invest a large amount of energy into reproduction, however they have different ways of doing this - mainly because females are the ones who carry the eggs/embryo to term.
Female investment
Females only have a limited number of eggs, therefore eggs are seen as a more valuable investment compared to sperm. Therefore, it is hugely important for females to ensure the sperm which will fertilize her egg is of a very high quality - this means she needs to be quite fussy about who makes the sperm! This type of selection means that males often compete for who mates with the female - the victor will gain access to the female, as they obviously have 'better' genes. |
Male investment
Males are always making sperm, they make thousands of sperm every day, so they are basically always ready to pass on their genes. It is not 'smart' for males to mate with one female and stay with them forever, as this is a huge limit to their reproductive success. It is in the interests of males to 'spread their seed' as far as they can, so males often mate with a female and then leave her and find another, and another, passing his genes on to many offspring! As the males don't get pregnant, and often aren't needed to help raise the offspring, they are free to go and attempt to produce as many offspring as possible! |
One method: males fight for the female (she doesn't pick the winner, the males fight it out!)
Males compete with each other for mates - the winner gets the girl! Competition in this form is more than agonistic behaviour, it is physical contact until either a) one of the males submits to the other, and leaves empty handed, or b) to the death. If neither party gives up, the latter is likely to happen as the injuries sustained in the fight can be fatal.
The winner gets to mate with the female, and can then go off and mate with more if victorious in more battles. Often by winning one battle, a male can gain access to the females in an area, rather than just one female. |
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Another method: males display for the female (female chooses the 'most attractive' male based on her own criteria!)
Males can compete with each other by performing amazing displays for the female, who then chooses the male who displays the best quality alleles. This is called sexual selection.
Species that employ this method of reproduction often have beautifully coloured males and dull females, as it is the males who need to do the displays, so those with the 'best' alleles often have the most beautiful appearance and they need to show it off in order to reproduce! Bright colours are likely to attract predators. Being a female with bright colours would be highly disadvantageous, as it would reduce the likelihood of her (and his) genes being passed on as bright colours would attract predators to the nest/home. When males and females of the same species are significantly different in size/colouring, this is termed sexual dimorphism. |
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Another method: males hold a 'mating territory' which multiple females visit (the better the territory, the more girls you get!)
A lek is a territory used solely for mating. A number of males gather together within this area and compete with each other for the 'best' mating spot - which is usually right in the middle of the territory. A hierarchy is formed within the lek, those most dominant get the best spots and the least dominant are pushed out towards the edges of the territory. There are no resources within a lek that are of use to the females - therefore they only enter this mating territory when they are 'in season' (fertile). They are attracted to the lek and choose to mate with the males who hold the best territories (they are the most dominant, therefore must have the best quality genes). The males can be chosen by several different females, allowing their genes to be passed on to several different offspring. After mating, the females leave the lek and rear the offspring on their own.
In the picture below, notice the males are bigger, more colourful and have beautiful tails? They are 'showing off' for the females (smaller, less colourful) who have entered the lek. The females will choose the males with the best territory and mate with them, then leave.
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Sexual dimorphism
Results from male competition for females. As the female has the longer-term investment, she wants the highest quality genes to be present in her offspring, so she will mate with the 'best' male. For some species, its the strongest and toughest male, like in the deer, so males have big horns for fighting and females do not. The male peacock spider has a flashy tail for his dance, the female doesn't dance for the male (he is trying to mate with anyone who will have him!) so she doesn't have a flashy tail! Often the males are appear 'prettier' than the females, due to sexual selection.
Co-operating
To be reproductively successful, which is the aim of all organisms (except altruistic ones, however they want other members of the colony to be reproductively successful), both the male and female need to reproduce.
Sexual reproduction involves a male and a female; sperm and egg, to create a viable zygote. The characteristics of sperm and egg:
To increase the likelihood of successful fertilization, sperm and egg must be released in close proximity to each other, at the same time. Therefore the timing of reproduction in both males and females of one species must be synchronized. It is easiest for this to happen if both individuals respond to the same environmental cue.
Sexual reproduction involves a male and a female; sperm and egg, to create a viable zygote. The characteristics of sperm and egg:
- sperm must propel themselves towards the egg - they can swim - but not very far and not for very long
- eggs, once released, do not remain fertile for very long
To increase the likelihood of successful fertilization, sperm and egg must be released in close proximity to each other, at the same time. Therefore the timing of reproduction in both males and females of one species must be synchronized. It is easiest for this to happen if both individuals respond to the same environmental cue.
Courtship helps animals of the same species prepare for reproduction
Courtship is type of behaviour that animals perform (species-specific behaviour) that precedes and accompanies mating. Some examples are in the videos below!
Courtship can involve different signals
Courtship is type of behaviour that animals perform (species-specific behaviour) that precedes and accompanies mating. Some examples are in the videos below!
Courtship can involve different signals
- Visual - i.e. most birds have elaborate displays of colour and movement
- Vocal - i.e. many birds, insects (e.g. crickets, grasshoppers) make particular noises to attract a mate
- Chemical - i.e. female moths using pheromones to attract male moths
- Touch - i.e. spiders who make webs - the male sends particular vibrations to the female spider through her web!
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Advantages of courtship behaviour:
- Ensures mating occurs between members of the same species - only same-species members recognize the behaviour and know how to respond. If mating occurs between members of different species (it does happen), offspring are less likely to be viable and is a waste of energy for both male and female involved.
- Courtship behaviour actually suppresses aggressive behaviour, which would normally occur when another same-species member neared the territory of another member. Reduces risk of injury as a result!
- For individual that form pair-bonds (stay together to rear offspring), courtship behaviour helps to develop this, making the rearing of young more likely to be successful
- Ensures each member is in a state of readiness at the same time, making reproduction likely to be successful. Rather than the male mating with the female when an egg is not ready - this is a waste of energy!
Reproductive strategies
The goal is to pass on your genes, after all!
r-strategyMany offspring low chance all will survive, but some are likely to
Those organisms described as r-strategists typically live in unstable, unpredictable environments. Here, the ability to reproduce rapidly (exponentially) is important. |
K-strategyFew offspring over lifetime, but all offspring highly likely to survive
Their reproductive strategy is to grow slowly, live close to the carrying capacity of their habitat and produce a few progeny each with a high probability of survival. Typical K-selected organisms are elephants, and humans. Usually this strategy is observed in stable environments. |
Parental care
The more care required by the offspring, the more likely that both parents will stay around and care for it. This increases chance of offspring surviving, therefore the reproductive success of the parents. The more care needed, the more likely parents will stay together to look after it.
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Parental care
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Offspring can be categorized based on their 'neediness'
- altricial - enter the outside world blind and helpless
- are characteristics of animals whose young are well protected
- e.g. rats and mice, humans
- precocial - are born in an advanced state and are able to run
- e.g. many groundnesting birds such as ducks, pukekos, other animals such as horses, giraffes
This leads to different strategies being employed by different species, relating to how much care the offspring require:
- monogamy
- polygyny
- polygynandry
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Monogamy
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Polygyny
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Polygynandry
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Monogamy is when each male mates with only one female in one breeding season, sometimes for his/their whole life!
Albatross pair for life this actually increases their reproductive success, which is why they do this! |
Polygyny is when a male mates with more than one female in one breeding season.
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Polygynandry is when a type of co-operative parental care where more than one adult is involved in rearing young.
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Reducing/avoiding intraspecific competition
There are 2 ways plants and animals do this
- dispersal
- niche differentiation
DispersalThis is a method for plants and animals who can't move much. By speading offspring out away from the parent plant or animal, competition is reduced between parent and offspring.
Adaptations for dispersal
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Niche differentiationWhen competition for resources is too high, some animals may
All of these things are ways that species who have closely overlapping niches can make them a little different and therefore reduce competition for one or more resources. If some animals left the group and moved to another location, this may lead to them becoming a new species this would take some time due to natural selection. |
New location = new resources to exploit
- those better adapted to these new resources will obtain more of the resource
- leads to more reproduction (lots of food = higher success rate or frequency of reproduction)
- more offspring produced holding genes that were passed on
- same genes that helped parent exploit new habitat
- the offspring can exploit habitat, high level of reproductive success
- genes that benefit individuals in this new environment become more common
- beneficial genes in this habitat = different to the previous habitat
- as more genetic differences accumulate between populations, could lead to them becoming so different that they could no longer produce viable offspring = speciation (next topic is all about this)