Chapter 5 Interactions in the Ecosystem

1. Chapter 5Interactions in the Ecosystem Habitat-the place in an ecosystem where an organism lives Organisms adapt to their habitat by the way they gather food, reproduce, and avoid predators Organisms also have a specific role in the ecosystem called a niche Niche-the role of an organism in the ecosystem, what the organism does, its “job” Niches must include biotic and abiotic factors: food sources, predators, temperature, sunlight and water amounts, time of day or night All members of a species have the same niche, two different species cannot share the exact same niche in the same habitat Niches can be similar though Different species of the Anolis lizard eat insects, but just different sizes. If two species try to share the exact same niche in the same habitat, they will be forced to compete.

2. There can be only one winner in a competition, so one species will be forced to move or die out This causes competitive exclusion-the extinction of a population due to the direct competition with another species for a resource The species is not extinct entirely, just from the location Fundamental niche- the entire niche that an organism could have Realized niche- the niche that the organism actually has Many times, one species will help define the niche of another species Ex: barnacle species Species A(Chthamalus stellatus), Species B(Balanus balanoides)

3. Niche Diversity The number of different niches in an ecosystem Niche diversity is often determined by abiotic factors Marshes have many organisms but very few niches(jobs) because the environment is constant Deserts have few organisms, but many different niches(jobs) because of harsher environment (temperature and moisture) Predator-an organism that actively hunts other organisms Prey-the organism that is hunted Predators decrease the population size of their prey species Now more resources are available to other species, so a new niche is formed Predators increase niche diversity Keystone predator- predator that promotes the increase in niche diversity in a habitat Ex: sea stars and mussels studied by Robert Paine

4. Evolution and Adaptation Evolution-a change in the characteristics of a population of organisms over time Within a species, the individuals have genetic variations Sometimes, a certain variation (characteristic) allows the individuals to produce more offspring Since the characteristic is genetic, it will be passed on from generation to generation More individuals in the species population will have this characteristic/trait Over a long period of time, these individuals with the changes, “adaptations”,will outnumber the others without the adaptation The species will have evolved

5. Evolution causes population to adapt to very specific niches in one environment This reduces competition with other species Ex: 5 species of warblers All live in spruce trees & prey on insects Difference is each species feeds on a different part of the tree Specialized species- a species with a very small niche Ex:koala bear and eucalyptus trees Specialized species are very vulnerable to extinction Generalized species-a species with a very wide niche Generalized species have several food sources Ex:mice and cockroaches Generalized species can survive a constantly changing environment by changing their behaviors to fit the new environment

6. Convergent Evolution-the independent development of similar adaptations in two species with similar niches In English, that means two different species that live in two different ecosystems develop similar adaptations because they both have similar niches Ex: birds and bats Each are a different species and can live in different ecosystems and habitats. What do both of them have? Both developed wings because their niche requires them to fly This development does not have to occur in the same time period Ex: dolphins(exists today) and ichthyosaur(extinct reptile from the Jurassic period) Both have adaptations for swimming (fins, streamlined body shape, pointed nose)

7. Coevolution-occurs when species that interact closely become adapted to one another In English, two species live and interact so closely that they change together Ex: plants and caterpillars Many plants have poisonous chemicals that most insects cannot resist, except for some caterpillars These caterpillars adapt and eat only on the poisonous plants The plants have made the poison, and the caterpillar adapted to the poison Sometimes both species will benefit from the coevolution Ex: acacia tree and stinging ants in Central and South America The acacia tree has hollow, pointed tubes that the ants live in and are protected from predators The ants attack animals trying to eat the acacia, clear vegetation around the tree so it gets more sunlight (why?) Now, the ants and the acacia tree need each other to survive

8. Populations Populations are controlled by biotic and abiotic factors Thomas Malthus(1798-England) observed that human population can quickly grow past what the environment can support--causing famine and disease He inspired Charles Darwin(On the Origin of Species) What does this mean? “There is no exception to the rule that every organic being naturally increases at so high a rate, that, if not destroyed, the Earth would soon be covered by the progeny(descendants) of a single pair.” Darwin said that organisms produce more offspring than the Earth can provide for. This leads to the organisms competing for resources Only the most “fit” with the best adaptations will survive. This is called natural selection

9. Population growth in which the rate of growth in each generation is a multiple of the previous generation is exponential growth Start with 2 elephants Next generation has 6 elephants Next generation has 18 elephants And on and on…… All populations have the potential to grow exponentially IF it has the perfect environment In reality, populations are limited by food, climate, predators and many other things Populations are limited to short growth periods and certain geographic areas Each ecosystem has a carrying capacity for every species in it. Carrying capacity=the number of individuals of a species that can be supported by an ecosystem

10. What happens as populations grow? Resources (food & living space) are used and become hard to find Competition starts among a species Death rate increases, birth rate decreases Population growth slows Population growth will eventually stop when #births = # deaths This can be graphed with an S-shaped curve (Fig. 5-9, pg. 81) Small population starts off growing quickly (exponentially) because of unlimited resources As population approaches its carrying capacity, growth slows Growth stops once it reaches its carrying capacity

11. Limiting Factors Carrying capacity has things that slow growth of the population= limiting factors If the factors affect populations more when the population grows, it is a density-dependent limiting factor (based on size of population) Ex: food supply, predation, disease, living space, water Factors that affect population growth regardless of the size are density-independent limiting factors(not based on size of population) Ex: climate, natural disasters, human disturbances Populations controlled by density-dependent factors show a S-shaped growth curve Populations controlled by density-independent factors show a boom-and-bust growth curve Population grows exponentially under favorable conditions, and then drops sharply when conditions change (insects: Fig 5.11 pg 83)

12. Human Population Growth Human growth has been exponential for a long time We have had continued growth because of advances in farming, technology, energy development, transportation, medicine Eventually, our resources will be depleted No population can grow exponentially forever What can we do to save resources?