Thanks to All Parents for the Spectacular Social Event for the 8th grade. It was wonderful and your hardwork is greatly appreciated. If you are missing a tray, I have some or if you mistakenly have someone else’s please return to me and I will find the owner.
Science notes for test on Tuesday 6/11
Notes Ch.21 Populations and Communities
An organism obtains food, water, shelter, and other things from its environment. An environment that provides the things the organism needs to live, grow, and reproduce is called its habitat.
. Biotic factors are the living parts of a habitat including grass, trees, other organisms .
Abiotic factors are the nonliving parts of an organism’s habitat. They include water, sunlight, oxygen, temperature, and soil.
Levels of Organization
- A species is a group of organisms that are physically similar and can mate with each other and produce offspring that can also mate and reproduce.
- All the members of one species in a particular area are referred to as a population.
- All the different populations that live together in an area make up a community.
- To be considered a community, the different populations must live close enough together to interact. One way the populations in a community may interact is by using the same resources, such as food and shelter
- The community of organisms that live in a particular area, along with their nonliving surroundings, make up an ecosystem.
The study of how living things interact with each other and with their environment is called ecology
Determining Population Size
Some methods of determining the size of a population are direct and indirect observations, sampling, and mark-and-recapture studies.
- The most obvious way to determine the size of a population is to count all of its members.
- Sometimes it may be easier to observe signs of organisms rather than the organisms themselves. Ex. Observing and counting mud nests on a cliff. If 4 birds inhabit each nest and there are 10 nests on the cliff you could estimate 4×10 = 40 birds.
- In many cases, it is not even possible to count signs of every member of a population. The population may be very large or spread over a wide area. In such cases, ecologists usually make an estimate. An estimate is an approximation of a number, based on reasonable assumptions.
- Another estimating method is called “mark and recapture.
Changes in Population Size
immigration- a species moves into a population
emigration- a species leaves a population
estimate - an approximate number based on reasonable assumptions
Births and Deaths
The birth rate of a population is the number of births in a population in a certain amount of time. The death rate is the number of deaths in a population in a certain amount of time. If 400 rabbits die in a year in the population, the death rate would be 400 rabbits per year.
The Population Statement
When the birth rate in a population is greater than the death rate, If birth rate > death rate, population size increases. However, if the death rate in a population is greater than the birth rate . If death rate > birth rate, population size decreases.
population density—the number of individuals in a specific area.
A limiting factor is an environmental factor that causes a population to decrease.
carrying capacity is the largest population that an area can support.
Some limiting factors for populations are
- food and water,
- weather conditions.
Adapting to the Environment
A characteristic that makes an individual better suited to its environment may eventually become common in that species through a process called natural selection. Natural selection works like this: Individuals whose unique characteristics are best suited for their environment tend to survive and produce offspring. Offspring that inherit these characteristics also live to reproduce. Natural selection results in adaptations, the behaviors and physical characteristics that allow organisms to live successfully in their environments. Individuals with characteristics that are poorly suited to the environment are less likely to survive and reproduce. Over time, poorly suited characteristics may disappear from the species.
Every organism has a variety of adaptations that are suited to its specific living conditions. The role of an organism in its habitat, or how it makes its living, is called its niche.
A niche includes
- the type of food the organism eats,
- how it obtains this food, and which other organisms use the organism as food.
- also includes when and how the organism reproduces
- the physical conditions it requires to survive.
There are three major types of interactions among organisms: competition, predation, and symbiosis.
- competition, the struggle between organisms to survive as they attempt to use the same limited resource.
- Predation-An interaction in which one organism kills another for food . The organism that does the kiling, is the predator. The organism that is killed is the prey.
- Symbiosis is a close relationship between two species that benefits at least one of the species. The three types of symbiotic relationships are mutualism, commensalism, and parasitism.
· Mutualism – A relationship in which both species benefit.
· Commensalism - A relationship in which one species benefits and the other species is neither helped nor harmed
· Parasitism - involves one organism living on or inside another organism and harming it.
- Primary succession is the series of changes that occur in an area where no soil or organisms exist. The first species to populate the area are called pioneer species. They are often carried to the area by wind or water.
- Secondary succession is the series of changes that occur in an area where the ecosystem has been disturbed, but where soil already exisits . Natural disturbances that have this effect include fires, hurricanes, and tornadoes. Unlike primary succession, secondary succession occurs in a place where an ecosystem currently exists.
Sect. 2 Assessment p. 718 1 a 2 abc 3 abc