1 5.1: How Populations Grow

2 Key Features of Populations When ecologists study changes in an ecosystem, they study it at the population level. population: group of individuals of one species living in one area at one time will study a number of features within each population

3 geographic range: area inhabited by a population can vary widely depending on the species House Sparrow Honduran Emerald Hummingbird

4 population density: number of individuals in a given area if they are too far apart they may only rarely encounter one another resulting in little reproduction Question: Which is more dense – US or Japan?

5 dispersion: way in which the individuals of a population are arranged Most common

6 age structure: number of males and females of each age in a population most plants and animals can’t reproduce until they reach a certain age only females can produce offspring

7 nearly all populations will tend to grow as long as there are resources available most basic factors that affect the rate of population growth are the number of births and the number of deaths growth rate = birth rate – death rate How do we see growth?

8 population growth can also be affected by individuals moving in and out of an area immigration: when individuals move into a population’s range ~ population will increase emigration: when individuals move out of a population’s range ~ population will decrease

9 exponential growth: population growth stays the same so the population size increases steadily looks like a “J” is the maximum population growth under ideal circumstances

10 includes unlimited resources (food, water, space, mates) and no predators No population exhibits this type of growth for long!

11 In reality, there is a limit to the number of organisms an area can support so growth will not continue forever carrying capacity: number of organisms of one species that an environment can support indefinitely

12 logistic growth: population growth that accounts for the declining resources available to populations as they grow looks like an “S” eventually birth = death so the population stops growing

13 this model shows how exponential growth will continue until the carrying capacity is reached for that environment

14 Exponential model (J- curve) occurs when there is no limit to population size. Logistic model (S-curve) shows the effect of the carrying capacity of the environment.

15 Invasive Species One of the greatest threats to biodiversity is the introduction of plants and animals that are not native to that area. These are known as invasive species. Because these organisms have no natural predators (controls), they can easily take over an area and push out all native species.

16 The impacts of invasive species are second only to habitat destruction as a cause of global biodiversity loss. Invading alien species in the United States cause major environmental damages and losses every year. US agriculture loses $13 billion in crops each year to invasives with a total economic loss estimated at $122 billion as of 2012.

17 Emerald Ash Borer – insect that kills ash trees

18 Confirmed in Lawrence County!

19 Zebra Mussel – bivalve (“clam”)

20 Grass Carp This 65 lb. 2 oz., 46.9-inch grass carp was landed by David Hughes of Indianapolis in a private lake in Morgan County. Hughes' record carp beat the previous Indiana grass carp record by nearly 24 lbs!

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