APES Notes Ch. 9. Mrs. Sealy. Major Characteristics of populations. size density Dispersion: clumped, uniform and random age distribution: Population dynamics: changes in size, density, dispersion and age distribution of a population. Clumped (elephants). Uniform (creosote bush).
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APES Notes Ch. 9 Mrs. Sealy
Major Characteristics of populations • size • density • Dispersion: clumped, uniform and random • age distribution: • Population dynamics: changes in size, density, dispersion and age distribution of a population
Clumped (elephants) Uniform (creosote bush) Random (dandelions) Fig. 9.2, p. 199
Limits on Population growth • A. Population change = (Births + Immigration) – (Deaths + Emigration) • B. Carrying capacity (k) = biotic potential + environmental resistance • C. Biotic potential: capacity for growth of a population. Example: flies – high biotic potential, pandas - low • D. Environmental resistance: all those things that limit the size of a population. Examples: fire, predation, lack of resources, disease
POPULATION SIZE Growth factors (biotic potential) Decrease factors (environmental resistance) Abiotic Abiotic Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients) Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients) Biotic Biotic High reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapt to environmental change Fig. 9.3, p. 200
Carrying capacity: • E. the maximum number of individuals of a given species that can be sustained in a given area indefinitely. When the carrying capacity of a population is exceeded, the population will have a dieback or crash to remove the excess animals. An example is: • The Reindeer of Angel Island
2,000 1,500 Number of reindeer 1,000 500 1910 1920 1930 1940 1950 Fig. 9.6, p. 201 Year
K Population size (N) Population size (N) Time (t) Time (t) Exponential Growth Logistic Growth Fig. 9.4, p. 201
2.0 1.5 Number of sheep (millions) 1.0 .5 1800 1825 1850 1875 1900 1925 Fig. 9.5, p. 201 Year
minimum viable population: • F. minimum population that a species needs to have to be sustained. You need a minimum number of individuals to support a population because: • 1. Too few individuals causes interbreeding • 2. They need to be able to find mates • 3. Not enough genetic variability for the population to adapt
G. Density and population growth: • 1. Density independent population controls are things that affect the size of a population that have nothing to with the density of a population. For example: • 2. Density dependent population controls are things that affect the size of a population that occur only as the density of the population increases. For example:
H. Population fluctuation curvesGraph of population curves – stable, irruptive, cyclic, irregular Irregular Stable Number of individuals Cyclic Irruptive Time Fig. 9.7, p. 202
160 140 Hare 120 Lynx 100 Population size (thousands) 80 60 40 20 0 1845 1855 1865 1875 1885 1895 1905 1915 1925 1935 Year Fig. 9.8, p. 203
5,000 Moose population Wolf population 4,000 3,000 Number of moose 100 90 80 2,000 70 60 Number of wolves 50 40 1,000 30 20 500 10 0 1900 1910 1930 1950 1970 1990 2000 Year 1997 Fig. 9.9, p. 204
Reproductive Patterns and Survival • III Asexual Reproduction: all offspring are exact genetic copies (clones) of a single parent. Example: bacteria, fungi • Sexual Reproduction: all offspring are a result of combining the sperm and ovum from both parents. This produces offspring that have traits from both parents. 97% of all known organisms.
r-Selected Species cockroach dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species Fig. 9.10a, p. 205
K-Selected Species elephant saguaro Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species Fig. 9.10b, p. 205
survivorship curves – life expectancy curve: shows number of survivors of each age group for a particular species • Graph Survivorship curve
100 10 Percentage surviving (log scale) 1 0 Age Fig. 9.11, p. 206
Conservation Biology • Multidisciplinary science of that uses the best information available to determine how to best protect species from extinction. • Determine which species are in danger of extinction, what the status of ecosystems is, what measures can be taken to preserve species.
Human Impacts on Ecosystems: • fragmenting and degrading habitats • simplifying ecosystems • strengthening some populations of pest species and disease causing bacteria • eliminating predators • introducing alien species • over harvesting resources • interfering with normal chemical cycling
Environmental Stress Organism Level Population Level Population Level Disruption of energy flow through food chains and webs Disruption of biogeochemical cycles Lower species diversity Habitat loss or degradation Less complex food webs Lower stability Ecosystem collapse Physiological changes Psychological changes Behavior changes Fewer or no offspring Genetic defects Birth defects Cancers Death Change in population size Change in age structure (old, young, and weak may die) Survival of strains genetically resistant to stress Loss of genetic diversity and adaptability Extinction Fig. 9.12, p. 208