Chapter 35.1 and 35.2 Populations

1. Chapter 35.1 and 35.2Populations by, Alex Kannel, Yanni Konstantinidis and Marina Guigli

2. Defining Populations BIG 3   (factors that influence a population's size)                 -"availabliltiy of food and space"                 -"weather conditions"                 -"breeding patterns" In order to properly understand how the BIG 3 affect different populations, a geographic boundary must be defined                 -natural boundary (e.g. a natural boundary for most fish  would be the edges of the ocean)                 -set boundary (e.g. a set boundary for humans would be a giant bubble like in the Simpsons Movie  or an aquarium for fish)

3. What is Population Density? -it is the number of individuals in a certain space -Population Density is often used to compare populations in different habitats Population Density= Beings/Units of Area Population Density of students in science classrooms=23/1 Classroom Population Density of students English classrooms=42/1 Classroom

4. Sampling Techniques -Scientists use different sampling techniques to keep measurements such as populations densities of different species similarly accurate -most often this number is not exact  (for it is almost impossible to count every living being of a species in one place at one time)     (e.g. the population density of trees in a forest can be more precisely recorded than the population density of  Largemouth Bass in a lake)  Some sampling techniques are: Creating quadrats, Indirect Counting and Mark-Recapture

5. Quadrats Quadrat=a specific boundary scientists create to count a species in -in order to keep their results accurate scientists perform this technique of sampling multiple times in different locations within the given ecosystem and average their findings -For example a scientist could cut a large rain forest into quadrats in order to accurately find the population density of tigers in the given forest

6. Indirect Counting Definition: A sampling technique that helps scientists count organisms that move around a lot or are difficult to see. -Unrealistic to count each organism in order to get a realistic population size. -Those organisms that move can be counted by their "homes"...nests, burrows or tracks. ex: birds (any evidence that they have been present)

7. Mark-Recapture Mark-Recapture: Tagging animals -Biologist trap animals and mark them. (animals can be marked with a drop of colored dye) -They then release the animals and then recapture more animals after a period of time. How does this tell you the population of the animal??? Formula: (# in the first capture) (# in second capture) Total population=       # of marked animals recaptured

8. A biologist captures 10 butterflies and marks them. After a period of time a biologist captures 15 butterflies. The biologist noticed he recaptured 5 of the origonal butterflies in the second trial (10)(15) = 30 butterflies        5 Mark-Recapture Example

9. Limits to Accuracy Accuracy can vary depending on the techniques a Biologist uses. Sources of error -Biologists can assume the organism is distributed evenly throughout the quadrant of study. ex: trees (estimates can be too low or too high) -Animals can become more contious of traps and unfimiliar areas from past experience. ex: Mark-Recapture...avoid being recaptured (prevention can be done by minimizing the effects of trapping the captured animals)

10. Exponential Growth of Populations Exponential Growth of Population= when population multiplies by the same number at equal time intervals This growth depends on two factors         -the organism's speed reproduction          -the organisms living conditions  e.g. bacteria can reproduce every 20 minutes in ideal conditions while human beings tend to take somewhere around 9 months to reproduce -exponential growth can be demonstrated on a graph in a line that forms a J ( y=2^x)         -One can see the exponential growth of populations easily with bacteria. They tend to split, under ideal conditions, at 20 minute intervals. Thus every 20 minutes their population is multiplied by 2

11. Carrying Capacity -Although many species populations can grow exponentially, eventually they will reach the limit of their natural resources, or their Carrying Capacity Limiting Factors- are the things that LIMIT the growth of a population            e.g. space, disease, lack of resources -Eventually the ratio of births and deaths will reach 1:1, keeping a population steady If one person dies every time one person is born how would population change?

12. Factors Affecting Population Growth -Many facts affect the growth of populations, such as: temperature, and food availability -A population of tropical fish would not be able to live in an arctic climate due to the difference in temperature -The population of bacteria in a petri dish, incubated indefinitely is directly related to the availability of the agar

13. Density-Dependent Factors -Factors that shift the population in correlation to how many creatures dwell in a set boundary are density-dependant factors -If a population of squirrels feeds specifically upon acorns, and the population of squirrels is small in comparison to the availability of the acorns then the squirrels will reproduce more -However, if the density of squirrels becomes too great for the acorns to support, one will expect to see a dwindling population

14. Density-Independent Factors -All factors that are not affected by the size of the population of a species are density-independent factors -Such factors include: droughts, blizzards, ice storms, flash floods, and hurricanes  Density Independent Factors are not affected by population density but actually affect it Density Dependent Factors are affected by population density and also affect it

15. Population Growth Cycles -Many species have "boom-and-bust" cycles, decrease sharply following a rapid increase -Some boom and bust cycles are directly related to the cycles of other species -If a species of lions feeds solely upon zebras, during the zebras boom the lions would experience a boom as well due to the increasing availability of nutrition -However, as the lions increase in number, so too do the deaths of zebras, causing both the zebras and the lions to bust

16. THANK YOU!!! QUESTIONS???