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ENV CHAPTER 8-1: HOW POPULATIONS CHANGE IN SIZE
Population – all the members of a species living in the same place at the same time-It is a reproductive group b/c organisms usually breed with members of their own population-It refers to the group in general and also its size (how many individuals) Properties of populations:1. Size – how many individuals there are2. Density – the number of individuals per unit area or volume3. Dispersion – distribution of individuals in a certain amount of space How a population grows- Increases with births, decreases with death.- Growth rate – the change in the size of a population over a certain period of timeo Growth rate = births – deathso Growths rates can be positive, negative, or zero How fast can a population grow?Biotic potential – the fastest rate a population can grow-It is limited by the maximum number of offspring an individual can produce (reproductive potential)-Different organisms have different reproductive potentials-Reproductive potential increases when individuals have more offspring at a time, reproduce more often and reproduce earlier in life- Reproducing earlier shortens generation time-Genertation time – time it takes an organism to reach reproductive age Exponential growth – the population keeps growing faster and faster- it only occurs when the population has plenty of food, space, and no competition or predatorsWhat limits population growth?-Natural conditions are never ideal or constant – populations can’t grow forever or rarely reach their reproductive potential-Carrying capacity – the maximum size of a population a particular ecosystem can support – this is a theoretical limit- Populations can increase past the number, but it can’t stay at the increased size – the population will crash – eventually it restabilizes around the limit again1. Resources limit populations – there’s only so much to go around Species reach the carrying capacity when they use a resource at the same rate the ecosystem makes it Such a resource is called a limiting resource2. Competition limits populations Direct – Members of a population can compete for a resource (like food) Indirect – members of a population can compete for territory or social dominancePopulation regulation – there are 2 kinds1. density dependent – organisms die depending on how crowded the population iso density-dependent factors include limited resources, predation, disease2. density independent – organisms die regardless of if it’s crowded or noto density-independent factors include severe weather, natural disasters
ENV CHAPTER 8-2: HOW SPECIES INTERACT WITH EACH OTHER
Niche – the unique role of a species within an ecosystemIt includes the organism’s physical home, the environmental factors that let the organism survive there, and its interactions with other organisms A niche is different from a habitatHabitat – place where the organism livesNiche – how the organism makes use of its habitat – the organism’s job in an ecosystem There are 5 ways species interact1. competition – when different individuals or populations try to use the same limited resource.Each individual has less access, so both species competing are negatively affectedIt can occur within and/or between speciesWhen different species compete – their niches overlap a. indirect – the species never come in direct contact (example – feeding on the same food but at different times, or plants that compete for pollinators) b. direct – individuals or species are in direct contact with each otherAdaptations to competition – adaptations that decrease competition are good for species whose niches interact- niche restriction – dividing up the niche in time or space- when both species are around, each uses less that it’s capable of using… but if one goes away, the other species takes it all up again. SUMMARY – species A and species B compete with each other. Both are harmed – they negatively affect each other. 2. predation – when an organism feeds on another organismPredator – the eater.Prey – the eaten.Populations of predators depend on populations of prey, so changes in one are usually linked to changes in the other.- adaptations to predation – many organisms evolve ways to avoid or defend against predators. Examples include camouflage, poison, mimicry. SUMMARY – species A feeds on species B. A benefits and B is harmed. 3. parasitism – when one organism lives on and feeds on another organismparasite – the feederHost – unluckyExamples include ticks, fleas, tapeworms, leaches, mistletoeParasitism is different from predator/prey b/c a parasite spends some or all of its life inside the host (whereas a predator just chomps on the prey)And the parasite can benefit if it lets the host live a while, but usually the host is weakened or exposed to disease. SUMMARY – species A feeds on species B. A benefits and B is harmed. 4. mutualism – when species depend on each other for survival – each species provides a benefit to the other.An example is the bacteria in your intestines SUMMARY – species A and B help each other. Both benefit.5. commensalism – one species benefits and the other doesn’t gain or lose anything.Examples incluse sharks and remoras, and birds nesting in trees. SUMMARY - Species A benefits from B but B is unaffected.Symbiosis and coevolutionSymbiosis – where 2 organisms live in close association. Usually at least one species benefitsEventually species that interact so closely co-evolve together This means that the species evolve adaptations that reduce the harm or improve the benefit from the relationship. Examples include flowers and pollinators.Google Sites
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