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POPULATION ECOLOGY What is a population? A group of organism of the same species living in an area List 3 different populations that would be found in this ecosystem. 1. ____Fox____________ 2. ______hawk___________ 3. ________squirrel________ Key Concepts: Population DENSITY is the _number__ of individuals in a population within a given area. Population GROWTH is the __increase____ in the size of a population over time. CARRYING CAPACITY is the __maximum__ number of individuals that an environment can support. (= k) There are certain factors that can control population density, growth, and carrying capacity. These are called LIMITING FACTORS. How do populations grow? There are 2 general trends: EXPONENTIAL GROWTH LOGISTIC GROWTH Graph: Graph shape: Description: __J_ - shape curve _S_ - shape curve means that as a population gets ___larger__, it also grows faster. shows that population growth stabilizes Examples: Bacteria, humans, Trees, animals, Limiting Resources? no Food, water, shelter, When populations are under the carrying capacity of an environment, births exceed deaths until the capacity is reached. In other words, there are more babies being ______________ than there are organisms _____________________. Logistic Growth: What is happening at… 1) Initial growth 2) exponential growth 3) carrying capacity Check for Understanding 1. What type of graph (growth curve) is this? logistic Check-for-Understanding: 2. What is the carrying capacity of the deer population ? 80 3. Explain why there might be a sudden decrease in the deer population once their numbers hit about 95. The ecosystem could not support that many individuals, so ‘some deer died off What kinds of things can affect whether a population exhibits exponential or logistic growth? Density – Dependent Limiting Factors Description: have negative effects as the population increases (Think about it: As the population grows larger and larger, disease is more easily spread, space becomes limited, competition increases, and food becomes more difficult to obtain. Hence, these density-dependent factors are affected by the size (or density) of the populatin). Examples: Density-Independent Limiting Factors affect every populations, regardless of the population size. Food, water, shelter, disease Natural disasters, hurricanes, forest fires, harsh winter, human intervention * What is the difference between density-dependent factors and density independent factors? ____________________________________________________________________________________________________________ ____________________________________________________________________________________________________________ How do limiting factors influence carrying capacity? Limiting Factor (density-dependent? density-independent?) Food availability (_density dependent) Example In a pond ecosystem, the level of algae determines the carrying capacity of a type of fish called carp. One summer the algae didn’t bloom as much because of a lack of sunlight. What would likely Competition (density dependent) Harsh winter density independent Disease density dependent happen to the carrying capacity of the carp? decrease_ Why? no food available Two species of birds live in the same woodland area. They both depend on lady bugs as their main source of food. One bird species is more effective at capturing the insects. How will the carrying capacity of this successful bird population compare to that of the other species? Population will increase, due to successful gathering of food. Other population will decrease, cannot compete successfully for food. One winter a huge blizzard wiped out a northeastern forest population of white rabbits. How would the carrying capacity of the wolf population (that preys upon those rabbits) be affected? The wolf population would decrease to do a decrease in their food supply In the winter it is well known that students are more likely to become infected with the influenza virus. Explain why this is so. Students are in close contact with each other and stay inside more, making it easier for the disease to spread Biotic Relationships within Ecosystems #1 Predator Pray Relationships 1. In year 15 the rabbit population began to increase. How did the fox population respond? _The wolf population eventually increased_ 2. What happens to the rabbit population then just after year 20? _it decreased rapidly Why? __________________________________ ________________________________________ 3. Why does the fox population never get as high or higher than the rabbit population? If there are more predators than prey, then both populations will eventually die out 4. Draw 2 new lines on the graph to predict how both populations will look by year 50. #2 Symbiotic Relationships Symbiotic Relationships Relationships where 2 different species have a close relationship with each other Mutualism Both species benefit Commensalism One benefits, the other is not affected Parasitism One species benefits, the other is harmed