Transcript Ecology
ECOLOGY Honors Biology What you will learn… 1. Ecology general overview. A. Definition B. Levels of Organization C. Abiotic vs. Biotic Factors 2. Populations A. Definition B. Population Density C. Population Structure and Dynamics D. Determining Population Growth E. Age Structure Communities and Ecosystems 1 A. Definition • Ecology is the study of how organisms interact with their environment and each other. This interaction of organisms is a two-way interaction. Organisms are affected by their environment, but by their activities they also change the environment. 1 B. Levels of Organization • Ecology is studied on several levels: – Organism • – Population • – Consists of all the populations of different species that inhabit a particular area. Ecosystem • – Group of individuals of the same species living in a particular geographic area. Community • – Ecologists may examine how one kind of organism meets the challenges of its environment, either through its physiology or behavior. Includes all forms of life in a certain area and all the nonliving factors as well. Biosphere • • • The global ecosystem; the sum of all the planet’s ecosystems. Most complex level in ecology, including the atmosphere to an altitude of several kilometers, the land down to and including water-bearing rocks under 3,000 m under Earth’s surface, lakes and streams, caves, and the oceans to a depth of several kilometers. It is self contained, or closed, except that its photosynthesizers derive energy from sunlight, and it loses heat to space. 1 B. Levels of Organization 1 C. Abiotic vs. Biotic Factors Abiotic components Physical and chemical factors (abiotic) affecting the organisms living in a particular ecosystem. Biotic components Organisms making up the community 1 C. Examples of Biotic Factors Anything that has the characteristics of life! Starfish Even bacteria! Polar bears Trees and grass 1 C. Examples of Abiotic Factors: Solar energy Water Temperature Wind Soil composition Unpredictable disturbances 2 A. What is a population? Populationa group of individuals of a single species that occupy the same general area. Rely on the same resources, are influenced by the same environmental factors, and have a high likelihood of interacting and breeding with one another. 2 B. Population Density – What is it? Population density The number of individuals of a species per unit area or volume For example, the number of oak trees per square kilometer (km2) in a forest or earthworms per cubic meter (m3) in forest soil 2B. Population Density- How do we measure it? In some cases, it is estimated by indirect indicators, such as number of bird nests or rodent burrows or even droppings or tracks. In rare cases, it is possible to count all individuals within the boundaries of the population. For example, it is possible to count the number of sea stars in a tide pool. Instead in most cases, ecologists use a variety of sampling techniques to estimate population densities. For example, they might base an estimate of the density of alligators in the Florida Everglades on a count of individuals in a few sample plots of 1 km2 each. The larger the number and size of sample plots, the more accurate the estimates. 2B. Population Density- How do we measure it? To measure population density, ecologists use a variety of sampling techniques to estimate population densities. In most cases, it is impractical or impossible to count all individuals of a population. Sampling Techniques: Point Sampling Transect Sampling Quadrat Sampling Mark and recapture (capture-recapture) 2C. Population Structure- Dispersion Patterns Within a population’s geographic range, local densities may vary greatly. The dispersion pattern of a population refers to the way individuals are spaced within their area. These patterns are important characteristics for an ecologist to study, since they provide insights into the environmental effects and social interactions in the population. Clumped Uniform Random 2C. Population Structure- Dispersion Patterns Clumped pattern Most common in nature Individuals are aggregated in patches Often results from an unequal distribution of resources in the environment. For example, plants or fungi may be clumped in areas where soil conditions and other factors favor germination and growth. Clumping of animals is often associated with uneven food distribution or with mating or other social behavior. For example, fish are often clumped in schools, which may reduce predation risks and increase feeding efficiency. Mosquitoes often swarm in great numbers, increasing their chances for mating. 2 C. Population Structure- Dispersion Patterns Uniform, or even, pattern Pattern of dispersion often results from interactions between the individuals of a population. For example, some plants secrete chemicals that inhibit the germination and growth of nearby plants that could compete for resources. Animals may exhibit uniform dispersion as a result of territorial behavior. For example, penguins and humans 2 C. Population Structure- Dispersion Patterns Random dispersion Individuals in a population are spaced in a patternless, unpredictable way. For example, clams living in a coastal mudflat might be randomly dispersed at times of the year when they are not breeding and when resources are plentiful and do not affect their distribution. Varying habitat conditions and social interactions make random dispersion rare. 2 C. Population Structure Life Tables Used to determine the average lifespan of various plants and animal species to study the dynamics of population growth. http://www.ssa.gov/OACT/STATS/table4c6.html 2 C. Population Structure Survivorship curves Graphs generated from life tables to make the data easier to comprehend. Plot the proportion of individuals alive at each age. • • • Type 1- produce few offspring, take care of their young, many survive into maturity. Type 2- intermediate, more constant mortality over the entire life span. Type 3- high death rates for the very young, mature individuals survive longer, usually involves very large # of offspring with little or no parent care 2 C. Population Structure Three types of survivorship curves 2 D. Determining Population Growth Population Growth The number of individuals comprising a population may fluctuate over time. These changes make populations dynamic. A population in equilibrium has no net change in its abundance. Population Growth = B – D + I – E • Factors that influence the number of individuals in a population: – – – – Birth (B) also known as natality Death (D) also known as mortality Immigration (I) Emigration (E) 2 D. Determining Population Growth The Exponential Growth Model The rate of population increase under ideal conditions. (High Birth Rate, Low Death Rate) Gives an idealized picture of unregulated population growth; no population can grow exponentially indefinitely. The whole population multiplies by a constant factor during each time interval. http://www.pbs.org/wgbh/nova/earth/global-populationgrowth.html 2 D. Determining Population Growth Logistic Growth Model (Carrying Capacity) A description of idealized population growth that is slowed by limiting factors as the population size increases. Limiting factors are environmental factors that restrict population growth. carrying capacity is the maximum population size that a particular environment can support or “carry” S-shape curve 1. Exponential Growth Phase-When the population first starts growing, population growth is close to exponential growth 2. Transitional Phase- The population growth starts to slow 3. Plateau Phase- Carrying capacity is reached and the population is as big as it can theoretically get in its environment 2 D. Determining Population Growth Logistic Growth Curves 2 D. Determining Population Growth 2 D. Determing Population Growth Factors that appear to regulate growth in natural populations: 1. Density-dependent factors: Competition among members of a growing population for limited resources, like food or territory. Health of organisms Predation Physiological factors (reproduction, growth, hormone changes) 2. Density independent factors • Regardless of population density, these factors affect individuals to the same extent. – Weather conditions – Acidity – Salinity – Fires – Catastrophies 2 D. Determing Population Growth Factors that appear to regulate growth in natural populations (continued): 3. Boom-and-bust cycles – the number of individuals within the population seems to show a cyclic change. Predator/prey relationships Changing food supply 2 E. Birth and Death Rates and Age Structure, OH MY! Human population can also be described by age structure diagrams. These diagrams are frequently dependent on the economy and social state of the country that they are measured in.