2 35.1 A population is a local group of organisms of one species I. Defining PopulationsA. A populations size is determined by the availability of food and space, weather conditions, and breeding patternsB. When scientists study populations they must determine its boundaries, such a lake, a state or the whole country
4 What is a species? Distinct form of life Population of organisms which can breed and produce offspring
5 Peacock + Peahen = Peachicks What about these?Peacock + Peahen = PeachicksHorse + Donkey = Mule
6 II. Population DensityA. Population Density is the number of individuals of a particular species per unit of area or volumeB.Population density is useful when comparing two populations in different areasClass Example.
7 III. Sampling Techniques A. Since it is impossible to count every member of a population scientists use sampling techniques to estimate the size of a populationQuadrats- scientists mark off a square boundary at several locations and take an average (plants)Indirect Counting- counting nests, burrows or tracks instead of the organisms themselves (insects)3. Mark-Recapture- scientists trap and mark individuals (birds)B. Most sampling techniques involve making assumptions about the populations being studied
8 Which sampling technique? Bats: mark-recaptureBlack bear: indirectCactus: quadrat
10 Which distribution pattern? Termite MoundRattlesnakeRandomClumped
11 35.2 Limits to population growth I. Exponential Growth of PopulationsA. A population’s ability to grow partly depends on the rate at which its organisms can reproduceB. Exponential Growth is when the population multiplies at a constant factor at constant time intervals i.e. bacteria doubling every 20 minutes
16 Transparency 35A-5 1. Compare and contrast the two growth curves. Both curves show a period of rapid population growth, but the fur seal population eventually levels off. The bacterial population appears to continue growing exponentially.
17 Transparency 35A-62. Which curve do you think more closely resembles the growth of most populations in nature? Explain.Limited growth curve; populations in nature are subject to limiting factors that prevent long-term exponential growth.
18 II. Carrying CapacityA population may start to grow exponentially, but eventually one or more environmental factors will limit its growthB. A limiting factor is a condition that can restrict a population’s growthC. The carrying capacity is the number of organisms in a population that the environment can maintain or “carry”
19 III. Factors Affecting Population Growth Density-Dependent Factors is a factor that limits a population more as a population density increasesB. Density-Independent Factors are factors that limit population but are unrelated to population density
20 Temperature and humidity Population GrowthTemperature and humidityFood availabilityDensity- IndependentDensity-dependent
21 IV. Population CyclingA “boom” and “bust” growth cycle is one that increases rapidly followed by a sharp declineB. Other growth cycles are influenced by those of other populations in their environments
32 I. History of Global Population Growth For most of human history, the human population has grown very slowly or not at allB. Human population growth depends on birth rates and death ratesC. The introduction of farming has provided a stable food supply so birth rates have gone upD. Advances in modern medicine, nutrition and sanitation have caused death rates to go downE. These factors have caused the human population to increase dramatically
34 Transparency 35B-21. Which age group forms the largest bulge in the age-structure graph of the United States? Of Kenya?40–44; under 5
35 Transparency 35B-32. Which country is likely to undergo the greatest increase in population in the next 20 years? Explain.Kenya; the majority of the population is under 25 years old, which is the portion likely to have children in the next 20 years.
36 II. Predicting Future Population Growth The Age Structure of a population is the proportion of people in different age groupsB. Prediction of future growth varies because of the difficulty predicting future birth and death rates of various countriesC. The question remains whether or not Earth will have the capacity for the human population
37 35.4 Species interact in biological communities
38 I. Competition Between Species Members of a population may compete for the same limited resourceB. Within a community, interspecific competition takes place when two or more species rely on the same limited resourceC. If two species are so similar in their requirements that the same resource limits both species’ growth it is called competitive exclusionD. A niche includes an organisms living place, its food source, the time of day it is most active and many other factors that are specific to that organism’s way of life
40 II. Predation Predation is when one organism eats another B. Eating and avoiding being eaten are important to survival and predators and prey have developed many adaptationsPredator adaptations include: being fast and agile, coloring that camouflages, hunting in groups, acute sense to find prey and having claws, teeth, fangs and stingers to help catch prey2. Prey adaptations include: retreating or fleeing from predators, camouflage, defensive coloring, mimicry, secreting poisonous chemicals, having spines and thorns
42 III. Symbiotic relationships A symbiotic relationship is when two species live in or on one anotherB. There are three main types of symbiotic relationshipsParasitism- A parasite gets it’s food at the expense of another organism, i.e. mosquitos and humans2. Mutualsim- Both organism benefit from the relationship, i.e. E.Coli and humans3. Commensalism- One organism benefits and the other is neither hurt nor helped, i.e. sharks and remoras
44 Symbiosis - Which is it? Predator-Prey Parasitism Mongoose & Cobra Liver Fluke
45 Symbiosis - Which is it? Commensalism Mutualism Clownfish & Anemone Air Plant
46 35.5 Disturbances in communities I. Disturbances to CommunitiesA. Natural Disturbances are events such as fires, volcanic eruptions, floods, storms, and droughts all destroy resources such as shelter and waterB. Disturbances can be either positive or negativeC. Humans also have an impact on communities which can be either positive or negative
48 II. Ecological Succession The series of changes in the species in a community, often following a disturbance is known as ecological successionThere are two types of succession:Primary succession which is when new community arises from a previously lifeless area i.e. plants growing on a volcanic island2. Secondary succession is when a new community arises from a previous community i.e. a forested area which has been cleared and abandoned
51 III. Human activities and species diversity 60% of the Earth’s land is used by humans, mainly for cropland or rangelandHumans usually have a negative effect on species in two waysClearing the Land- Humans clear vast amounts of land to make way for farming and building2. Introduced Species are species that are moved from one location to another either accidentally or on purpose. These new species may take over an area and prey on native species or drive them from their niches