Population Ecology Part 1
AP Biology Population Ecology Part 1 The human population will soon be over 7 billion people on Earth.
Population Ecology This field of Biology deals with species populations and the populations environment. A Population is the same species, same time, same place, and showing signs of reproduction. The human population will soon be over 7 billion people on Earth. We reached 7 billion as of October 2011current figures are 7, , , Population Human Population on Earth 8 Billion (2024) According to the most recent United Nations estimates, the human population of the world is expected to reach8 billion people in the spring of 2024. 7 Billion (2011) According to the United Nations, world population reached7 Billion on October 31, The US Census Bureau made a lower estimate, for which the 7 billion mark was onlyreached on March 12, Billion (1999) According to the United Nations, the6 billion figure was reached on October 12, 1999(celebrated as theDay of 6 Billion). According to the U.S. Census Bureau instead, the six billion milestone was reached on July 22, 1999, at about 3:49 AM GMT. Yet, according to theU.S. Census web site, the date and time of when 6 billion was reached will probably change because the already uncertain estimates are constantly being updated. Previous Milestones 5 Billion: 1987 4 Billion: 1974 3 Billion: 1960 2 Billion: 1927 1 Billion: 1804 Population Ecology It mainly focuses on Density (number of organisms in a given area) and boundaries. Man made boundaries or natural boundaries exist. Dispersion This term refers to where within the boundaries are the organisms located. Population Density Mark-Recapture Method
Measuring Density Mark-Recapture Method N= #Captured and marked in first group x total of second group that is caught # Recaptured from first time N is the estimated population size for that defined area. Patterns of Dispersion https://www.youtube.com/watch?v=6K128gg6Soc
Clumped This usually results from a need for nutrients, mating, or employment. (humans, elephants, fish, some species of plants, fungi) Uniform (evenly) This usually results from territoriality or favorable environment. (snakes, nesting birds, some plants,) Random There is no apparent reason seen in the dispersion pattern. (dandelions, Dispersal Patterns Demography The study of population sizes and distribution.
Growth This occurs by birth or immigration.(to enter into a new area). Decline This occurs by death or emigration (to exit an area). Life Tables Provides Age Specific Traits for cohorts (individuals of the same age or demographic). These are expensive and time consuming to produce. (Like the U.S. census.) Demography Terminology
Births Immigration Population size Emigration Deaths Life Tables and Cohorts Survivorship Curves - probability of newborn individuals surviving to a particular ageThree basic types of curves can exist in nature. Type I (Many young numerous middle few old)(type of environment?) This environment favors the young and usually indicates that the environment is favorable and these organisms are usually at the top of food chain and there seems to be extensive parental care and energy investment. Type II (Constant decline) (type of environment?) This indicates that the environment is relatively favorable but the organism may be a food source for another organism. The parental cares is modest. Type III (Many young few middle and old (type of environment?) This indicates a harsh environment because most of the young die at an early age. This indicates that they are a food source that is low on the food chain as well as have practically no parental investment. Young are left to fend for themselves. Figure 46.4a (Late loss) (Constant loss) (early loss) Survivorship Curves E. Reproductive tables 1. These tables are only concerned with females of reproductive age or possibility. These are the only real individuals who will be able to impact a population size since it is the female who provides the birth. (Low # of females indicates a threatened or dying population; High # indicates a thriving population.) Population Ecology Part 2
AP Biology Population Ecology Part 2 21 Important concepts from previous units:
Traits within cells or organisms are directly associated with inherited DNA (genes). DNA is inherited from the parents by fertilization occurring between a sperm and egg. (sexual reproduction) Positive feedback loops enhance a process that is already in action. DNA Inherited 23 Expression of DNA to create traits
24 Life Histories A life history can tell a lot about a species fitness. Traits needed for survival in a particular environment can be determined. Two types of life histories can typically be seen: Semelparity (Big Bang) Reproduce one time with huge numbers of offspring. Organism usually dies after reproducing, so it went out with a Big Bang. Tremendous amounts of time, energy, and resources invested in making numerous offspring. This type of history usually indicates a harsh environment and low survival rates. Examples: Salmon or Century Plant Century Plant 26 Natural selection is very obvious with Semelparitystrongest survive.
Iteroparity - Repeated Reproduction year after year. (Applies to most organisms usually.) This history indicates a favorable environment and good survival rates. Modest time, energy, resource investment are required. Environmental Conditions and survival rates? Environment is directly related to time, energy involved, resources available. Compromises (When, how often, how many)(Natural selection?) Natural selection is very obvious with Semelparitystrongest survive. Natural selection with Iteroparity is directly related to competition. Population Growth Models
Exponential Growth Models (Ideal Growth) Involves r-selection species. (r- think rapid growth)(A.K. A. Density independent) There population size is related to resources not number of organisms. Produces a J curve graph. Environment has unlimited resources. (Good for ideal growth) Occurs mainly in a new environments and pioneer species such as bacteria, lichens, and mosses. (They are the first organisms to colonize the new environment.) Population Growth Characteristics
Exponential Growth-as a population gets larger, it also grows faster (J-shaped curve) (WHY?) Elephant population 1900 1920 1940 1960 1980 Year
Exponential Growth 8,000 6,000 Elephant population 4,000 2,000 1900 1920 1940 1960 1980 Year 31 This is in areas that are just formed like Hawaii was millions of year ago. (Hawaii started as barren rock, until the pioneers arrived and began to make soil. The soil enabled plants to grow. The seeds of the plants arrived in the bird dropping of birds that stopped while migrating to feed on the mosses and lichens. Larger plant roots sped up soil formation to allow for larger plants.) Hawaii millions of years ago
33 Pioneer species begin to colonize (lichens and mosses)
34 Then over time, grasses begin to grow.
35 Then over time, shrubs will appear and they will be followed by trees.
36 Hawaii today 37 = (bN) (dN) (birth rate death rate) (This is equal to rN.)
N/t = B D (Means change in population is equal to births deaths in that time.) = (bN) (dN) (birth rate death rate) (This is equal to rN.) = rN; r= b d (if r is positive = growth greater; if r is negative = death greater) ZPG (Zero Population Growth) (r= 0) Intrinsic growth = rmax (Population is growing as fast as possible/doubling. This is seen as the curve begins to make a straight up curve.) r=rate of increase =b-d rN-rate of increase x number in population
B = bN b(per capita birth rate) N (population size) B expected number of birth expected based on the population size D=dN d(per capita death rate) D expected number of death expected based on the population size bN-dN=rN r=rate of increase =b-d rN-rate of increase x number in population Current population growth rate Formulas related to population growth
Growth rate (r) = birth rate (b) - death rate (d) # of births / total # of deaths / total Practice Problem: In research on beetles, you estimate that the populations size is Over the course of a month, you record 400 births and 150 deaths. What is the growth rate (r)? Population growth = rN (r = growth rate, N = original population size) Calculate the population growth of the beetle population. US Population size in 2013 (N) = approximately 316 million
Number of births in the US in 2013 (B) = approximately 4.1 million Number of deaths in the US in 2013 (D) = approximately 2.5 million What is theper capitabirth rate ("b") for the US in 2013? b=4.1 milliin /316 mil=.013=13/1000 What is theper capitadeath rate ("d") for the US in 2013? d=2.5million/316 million = .008 = 8/1000 Exponential Ideal Growth
42 Intrinsic Growth 43 Logistic Growth Model (Realistic growth)
1. Involves K-selection species usually. (K refers to a population that is hovering around the carrying capacity which is represented by K) (Density dependent) These species numbers are about number because there are limited resources because the species is near the carrying capacity for that environment. 2. Produces an S curve graph. (snakes around the carrying capacity line) 3. Environment has limited resources; that is why organisms stay around the K. a. More organisms than K means damage will be done to the environment. b. More damage done to environment can cause K to drop even farther. This can be an example of a positive feedback loop. c. Wars, disease, and famine breakout in a population to bring numbers down below K. (Extinction is possible? depends on damage to environment and K.) Carrying Capacity-the number of one species an environment can support over long periods of time.(S-shaped curve Logistic realistic growth
46 4. dN/dt = rN (K-N/K) K-Nthe number of individuals that environment can still support K-N/Kthe fraction of K still available for growth (As a population N approaches K, K-N approaches zero.) Meaning when K- N is equal to 0 you are at the carrying capacity for that environment.When K- N becomes 0, the whole equation becomes 0. Before this time, a population is experiencing exponential growth so you have r maxed. Logistic Growth 48 5. Lag time (This accounts for the overshoot
5. Lag time (This accounts for the overshoot.) It takes time to begin to see the effects. (So the line goes above K and this is when death, war, disease, and famine accelerate.) 6. Allee effect This situation occurs when you have a small number of organisms.This low number causes inbreeding to occur and then this results in no variation for a gene pool and this leads to increased genetic diseases that can be lethal to accumulate in the already small population and then the population enters what is referred to as the Extinction Vortex.It is extremely difficult to break out of the vortex. (Like a black whole of extinction.) Allee affect and the Extinction Vortex
Small population Genetic drift Inbreeding Lower reproduction Higher mortality Loss of genetic variability Reduction in individual fitness and population adaptability Smaller population 50