Populations and Communities

Do now- Monday Information: Tropisms are plants responses to stimuli. Stimuli can include sunlight, gravity, elevation, and many other factors by which a plant needs to respond by growing differently. Cypress trees grow in higher elevations where a lot of water is available. Scenario: I was at a music festival in the hill country of Texas. Expecting to see a lot of grassland and cacti, we were actually in the woods surrounded by tall cypress trees. Questions: 1. Why do you think cypress trees were able to grow there? 2. What kind of elevation do you think we were at? 3. How would the different trees affect other organisms in the same food web?

Thought Question In the last century, the piney woods of northwestern and central Louisiana were logged extensively by timber companies. A once vast forest was left with only a few areas intact, while all around, timber wasteland lay open with its wildlife decimated. In the 1930s, the US Forest service began purchasing what would amount to 604,000 acres of piney woods spread out across 5 management districts. The Forest Service dedicated the land to ecosystem restoration. Describe how the land area changed after the restoration effort. Be specific.

The effects of preservation

Ecology The branch of biology that studies the relationships of species with each other and their environment. Biology is a subcategory of ecology.

Biome An ecosystem with the same climate, ecosystem

Ecosystem The biotic factors in a biome

Community Group of populations living in a geographic area

Population All of the individuals of a species that live and reproduce in a given area

Individual One organism in a particular population

Thought Question Describe your status in the different spheres (starting at individual and working outward).

Thought Question 1 Describe some biotic and abiotic facts in the Kisatchie National Forest. Use the Forest’s website as a resource.

Habitat versus niche Habitat= The environment in which a population lives and provides the four things all species need to survive: food, water, shelter, and space Niche= The place where a population lives and the jobs that is performs within a community and a habitat

Thought Question 2 Predict what would happen if two species began competing directly for resources within the same niche.

Competition When two or more organisms need to use the same resource at the same time. Can occur between two species and within members of a population.

Predation When one animal pursues and uses another animal as a source of food.

Symbiosis More complex interaction taking place between species Parasitism Mutualism Commensalism

Parasitism One organism benefits as the other organism is harmed

Mutualism Both organisms benefit

Commensalism One organism benefits and the other organism is neither harmed nor helped

Limiting Factor #1 Predation

Thought Question In the early twentieth century, the US government wanted to increase the deer population of the Grand Canyon. To accomplish this, government officials wiped out the Grand Canyon’s wolf population. Describe two effects that this action most likely had on the deer populations.

Limiting factor #2 Food supply

Other limiting factors

Population Density Population density refers to the concentration of individuals living within an area. Divide the number of individuals in an area by the total area.

Thought Question A garden that is 50m2 is plagued by a population of roughly 2,500 caterpillars. Calculate the population density of the caterpillars in numbers per square meter. Explain how the size of a population in a habitat differs from the density of the population in a habitat.

Scientific Method Scientists can count the number of individuals in a population Or they can count the number of individuals in a small area then multiply that figure to estimate the total number of individuals in a habitat.

Thought Question When does it make more sense to estimate the number of individuals in a population rather than counting them all?

Changes in population size Population size is never constant Mortality refers to the death rate Natality is the birth rate

Thought Question In the US, the mortality rate for humans is about 2.4 million per year. The natality rate for humans is about 4 million per year. According to the mortality and natality rates, is the human population increasing or decreasing? In addition to mortality and natality rates, what processes could be changing the human population in the US?

Other population-changing factors Immigration= individuals moving into a habitat (remember In) Emigration= individuals leaving a habitat (remember Exit)

Thought Question Suppose that over the course of a year, a population of rabbits experiences the following changes in its population: 25,000 individuals die, 20,000 individuals are born, 15,000 individuals emigrate, and 20,000 individuals immigrate. By how much did the population of rabbits change in one year?

Invasive species New species that enter a community and don’t “fit in well” with the other species