http://www.hotelsbible.com/travelblog/wp-content/uploads/hotelsbible.com/animals-elephant-herd-drinkingafrican-safari-botswana.jpg POPULATION BIOLOGY
3 characteristics of a population: 1. Geographic distribution: the area inhabited by a population. 2. Population density: the number of individuals per unit area. 3. Population growth: Affected by the # of births, the # of deaths and the # of individuals entering (immigration) or leaving (emigration) the population. Populations grow if the birthrate is greater than the deathrate.
Linear Growth Population grows at a constant rate. The same number of individuals is added to a population in a given time period. Ex. A population of swallows grows by 10 birds each year. Year 1: 10 birds Year 2: 20 birds Year 3: 30 birds Year 4: 40 birds http://www.maths.mq.edu.au/texdev/mathsymp/honey/honey4.gif
Exponential Growth Unrestricted increase in populations Increase in population size is proportional to present size Produce J-shaped graphs (Jcurves); r-adapted Ex. Some bacteria can reproduce every 20 minutes (100% growth). 12:00 100 bacteria 12:20 200 bacteria 12:40 400 bacteria 1:00 800 bacteria 1:20 1600 bacteria 1:40 3200 bacteria 2:00 6400 bacteria http://www.maths.mq.edu.au/texdev/mathsymp/honey/honey6t.gif
Exponential growth AKA biotic potential the potential of a population to grow if nothing limits its size. Doubling time divide population size by the annual percentage growth this tells you how long it will take a population to double in size Ex. A deer population of 70 individuals is growing by 10% each year. How long will it take for the population to double? 70/10 = 7 years
In the Real World There are limits to growth The maximum number of individuals of a species that can be supported by a particular ecosystem is its carrying capacity Populations often overshoot the carrying capacity, and individuals die population crash Populations may fluctuate around carrying capacity with overshoots and diebacks common boom & bust cycles
Carrying Capacity
Logistic Growth Population size is regulated Population reaches equilibrium with its environmental resources and maintains a stable population size May begin as exponential, but growth rate slows as population reaches the carrying capacity of its environment http://www.geo.arizona.edu/antevs/nats104/00lect21grolog.
Logistic Growth http://www.bio.miami.edu/dana/pix/logisticpopns.gif
R-adapted vs. K-adapted species Opportunisitc or R-adapted species Short life Fast growth Mature early Many, small offspring Little parental care and protection Low trophic level Competitor or K-adapted species Long life Slower growth Mature later Few, large offspring High parental care and protection High trophic level
Limiting Factors
Limiting Factors Density dependent factors factors that depends on the population size. -increasing effect as population size increases disease, competition Density independent factors affects all populations equally, regardless of the population size temperature, drought, floods
Density-dependent limiting factors: 1.Competition: when the demand for resources such as food, water, space, and other essentials exceeds the supply. Some organisms avoid competition by migrating seasonally to areas where climate is better and more food is available
2. Predator-prey relationships: controls numbers of predators and prey 3. Parasitism and Disease: crowding leads to an increase in parasitism and resistance to disease.
Density Independent Limiting Factors 1.Unusual weather: such as extreme hot or cold temperatures 2. Natural disasters: such as hurricanes, tornados, floods, or droughts. 3. Human activity: such as damming a river or clear-cutting a forest
Spatial Distribution Clumped - many areas with many individuals, many with few. Random - some areas with many individuals, some with few. Uniform (Even) - all areas with same or nearly the same number; same distance between
Clumped distribution could result from individuals using a common resource that is in itself clumped (like buffalo around water holes).
Even distribution could result from individuals competing for a limiting resource (like creosote bushes in the desert).
Carrying Capacity in the Classroom You each now represent a cougar the classroom is your habitat. Your assigned seat is your den. To survive, you must hunt for food. Each cup represents a food item. You will need to sneak up on your prey (walk) and bring it back to your den. You can only carry ONE food item at a time back to your den.
Carrying Capacity in the Classroom To survive for about a month, you each need to bring back 50 kg of food. Food items in this habitat: S ( squirrel = 1 kg ) R ( rabbit= 2 kg ) P ( porcupine= 7,5 kg ) B ( beaver= 20 kg ) D ( deer= 75 kg )
Carrying Capacity in the Classroom Volunteer 1 You have been injured by a porcupine and are blind. Wear a blindfold as you hunt. No peeking! Volunteer 2 You tackled a big buck and broke your leg. Hop on one foot as you hunt. Volunteer 3 You have two cubs back in your den. Be sure to bring back enough food for everyone! (100 kg total)
Carrying Capacity in the Classroom Remember, cougars stalk their prey no running! In the wild cougars don t fight over food. The resulting injury may kill them. Start hunting!
Carrying Capacity in the Classroom Count up your food items remember, you need 50 kg to survive. Write down how much food you collected (total in kg) S ( squirrel = 1 kg ) R ( rabbit= 2 kg ) P ( porcupine= 7.5 kg ) B ( beaver= 20 kg ) D ( deer= 75 kg )
Carrying Capacity in the Classroom How many cougars survived? This is the carrying capacity of our habitat. What factors could affect the carrying capacity of this habitat? What do humans compete for? Is there a carrying capacity for humans?
In the early 1900 s, a few deer were brought to Angel Island. They rapidly multiplied to about 300 deer. This was far beyond the carrying capacity of the island, and many deer were starving. Concerned citizens brought the deer food from the mainland. This only made things worse. Excess animals trampled the soil, ate the bark off of trees, and destroyed seedlings of all kinds. The carrying capacity of the island was actually decreasing as the habitat was Real-world Example Angel Island
Angel Island State game managers proposed that the excess deer be shot by hunters. Protesters thought this was cruel. Then managers proposed that coyotes be imported to the island they d kill young fawns. Protesters also thought this intervention was wrong. In the end, 203 deer were caught and trucked miles away to other areas suitable for deer. 85% of these animals died within a year.
Cultural Carrying Capacity Some consider the human carrying capacity to be 50 billion. The current population is 7 billion. What would life be like with nearly 10 times as many people on Earth as there are today? If we consider supporting cultural luxuries such as eating meat, living in houses with yards, street lights, owning cars, heating buildings, higher education, etc. this reduces the carrying capacity cultural carrying capacity Cultural carrying capacity < simple carrying capacity
Cultural Carrying Capacity What do we do? Maximize the number of human beings living at the lowest possible level of comfort or optimize the quality of life for a much smaller population?