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SUCCESSION EQ: How does succession lead to a climax community? Succession • Primary Succession • Occurs in places where life has never existed before • There is no soil! • Pioneer species are the first species to arrive • Often moss or lichen (Freddy Fungus took a LICHEN to Alice Algae and now their relationship is on the rocks) • Clings to the rocks and breaks it down to create soil • Secondary Succession • Occurs where life has previously existed but was wiped out for some reason • SOIL IS AVAILABLE! • Both types of succession end in a stable climax community http://www.nps.gov/media/photo/gallery.htm?i d=3EB5B850-155D-4519-3EC97FCF1D50262A POPULATION GROWTH EQ: How do populations impact the environment? How does the environment impact populations? Exponential Growth • The simplest form of population growth is exponential • Population growth that expands faster and faster • 2 becomes 4 becomes 8 becomes 16 becomes 32… • This does not realistically occur Logistical Growth • Growth in which there are a series of phases and ends in a steady state where the number of individuals leaving the population is equal to the number of individuals entering the population Points of a Logistical Growth Curve • A : The species is first introduced to the environment • Growth is slow • B : A period of exponential growth occurs • C : Growth slows • D : population growth reaches a peak – the maximum number of individuals that can survive in the environment • E : Steady state Terms • Growth occurs when birth rate is higher than death rate • Steady state is when there is no population growth on average • Carrying capacity is the average number of individuals in a population at steady state Limits to growth • There are two types of limits to population growth – density dependant and density independent. • Density dependant means that the extent to which a factor limits population growth is dependant on the amount of individuals already in the population • Density independent means that the factor limits population growth regardless of the number of individuals already in the population. • A limiting resource is something that each organism needs to live and which is in limited supply • Food is such a resource Density Dependant Factors • Competition • If there is only a limited amount of resources available to the individuals they will compete for them • Only the strongest individuals in a large population will get use of the resources and be able to have young • Called intraspecific competition if it occurs within a species Density Dependant Factors • Predation • The act of one organism eating another • The organism doing the eating is the predator and the organism being eaten is the prey • Causes a decrease in the prey population • If the predators don’t eat too many individuals than birthrate can replace those that die keeping the population in steady state • If the predation is intense the population decreases • The number of prey and the number of predators are inter related – if the predators eat all the prey they will begin to starve to death; if the predators are scarce than the prey can have a jump in population Predator – Prey Relationships • Prey are introduced to the environment – multiply and are happy • Predator population increases because of plentiful prey • Prey population decreases because of plentiful predators • Predators population decreases because of lack of prey • Prey population increases because predator population decreased Good News • Predators often have a lot of variety in their diet and therefore the fluctuations between predator and prey interactions are not usually this dramatic • Some predators only take a bite out of the prey allowing it to survive another day • Most prey items usually have some defense against being eaten Density Dependant Factors • Parasitism • One organism lives on or in another organism eventually causing harm to the host • Very few marine organisms are parasite free • Parasites can be spread among individuals so the larger the population the greater risk for any one individual to die of a parasite Density Dependant Factors • Crowding and Stress • The more individuals in a population the faster they use up the limited resources available to them • Eventually there is not enough resources left to support any more individuals so the population levels off • The more crowded a population the more stress comes into play weakening immune systems and making individuals more prone to illness Density Independent Factors • Climate is the main density independent factor that affects organisms • El Nino which raises or lowers the water temperature can affect food sources Geographic Distribution • Main factor in determining population size • Where a population is located across the Earth