Ch. 55: Ecology of Individuals and Populations: Powerpoint Notes - Environmental Challenge o Ecology: how organisms relate to one another and to their environments o elements of environment: food, water, sunlight, soil o homeostasis  steady internal state regardless of external  ex: beetles catch water to survive in dry areas  some animals adopt surroundings (temperature, salinity, ect) o short term: few minutes to lifetime o long term: NS adapts population to environmento coping mechanisms  physiological responses- sweating, increased erythrocyte production, ‘antifreeze’ morphological capabilities - endotherms minimize energy expenditure; thick fur in winter behavioral responses- migration, maintaining body temperature o NS leads to evolutionary adaptation  Closely related species in different environments  Allen’s Rule: mammals from colder climates have shorter ears and limbs  Ex: desert frogs evolved a reduced rate of water loss through skin - Populations o Groups of individuals of the same species in one place o Characteristics… Population range: area throughout a population occurs  Pattern of spacing of individuals  Population size changes throughout time o Range  Most species have limited geographic range - Ex: devil’s hole pupfish lives in a single spring in southern Nevada - polar bears are well adapted for Arctic, so they don’t live inthe tropics ranges change through time - environmental- colonize suitable, previously unoccupied areas- humans have expanded ranges of coyotes  dispersal mechanisms- lizards colonized islands due to individuals or eggs floatingon vegetation- seeds of plants o Spacing Patterns  random spacing: individuals don’t interact strongly with each other; not common in nature  uniform spacing: behavioral interactions, resource competition  clumped spacing: uneven distribution of resources; common in nature  Meta-populations: areas where suitable habitat is patchy and separated by unsuitable habitat- Dispersalo Unsymmetrical interactiono Populations increase and send out disperserso Small populations have few disperserso Individual populations may become extinct o Population bottlenecks may occur - Source-sink meta-populations o Some areas are better suited for habitat than others o Populations in better areas (source) bolster populations of poorer areas (sink)- Implications o Continuous colonization of empty patches prevents long-term extinction o Species occupies larger area than it otherwise mighto Ex: Glanville Fritillary Butterfly  Individual populations are too small to survive on their own, but meta-population can- Population Demography o Demography: quantitative study of populations and how they change over time o Size changes as a whole (increasing, decreasing, constant) or in parts (birth and death rates of ages) o # of females directly related to # of birthso Generation times: average interval between births of an individual and birth of its offspring Short generation times can increase more quickly than long generations  Larger organisms generally have longer generation times o Age structure  # of individuals in a different age group  cohort: group of individuals of the same age  fecundity: number of offspring produced in a standard time  mortality: death rate in a standard time  age structure has a critical influence on a population’s growth rate o life tables show probability of survival and reproduction through a cohort’s life o survivorship: % of an original population that survives to a given age o survivorship curve: express some aspects of age distribution -Life History o NS favors traits that maximize number of surviving offspring left in the next generation by one organism Factors-How long an individual lives -How many young it produces each year Complete life cycle of an organism Trade-off: limited resources vs. increased reproduction o Balance between number of offspring and size of offspring Larger offspring  greater chance of survival Many small offspring  low survival rate o Age at first reproduction correlates with life span Long lived  delayed reproduction -Juveniles gain experience before high cost of reproduction Short lived  early reproduction -Time is important; delay could mean no offspring-Environmental Limits to Population Growth o Populations often remain the same size regardless of offspring borno Exponential growth model (no growth limits): r = (B-d)+(i-e) R = rate of population increase B = birth rate D = death rate I = immigration E = emigration o Biotic potential: e = I and there are not limits on growth then… dN/dt = riN N is the number of individuals in the population dN/dt = rate of change over timeri = intrinsic rate of natural increase for population (innate capacityfor growth) biotic potential for any population is exponential -unchecked exponential growth results in population explosiono all populations eventually reach a limit o Carrying capacity (K): maximum number of individuals that the environment can support o Logistic growth model (populations as they reach K) dN/dt = rN (K-N)/K dN/dt = intrinsic rate of natural increase adjusted for available resources as N approaches K, population growth rate slows N=K, population growth rate is zero -If population exceeds K, population size will decline until itreaches K -Factors that Regulate Populations o Density-dependent: factor that affects the population and depend on population size o Density-independent: other factors such as natural disasters affect populations, regardless of size rate of growth of a population is limited by something unrelated to size of the population ex: cold winters, droughts, storms, volcanic eruptions -cause erratic growth patterns o ex: North American snowshoe10 year cycle in which populations fall 10 to 30 fold and 100 fold changes can occur factors: food plants and predators o resource availability limited resources  high reproduction cost -selection favors individuals that can compete and efficiently utilize resources -can lower reproductive rates -K selection populations: adapted to thrive when population is near carrying capacity Populations far below carrying capacity have abundant resources-Low reproduction costs-R-selection populations: selection favors individuals with the highest reproductive rates -Most natural