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3: POPULATION DYNAMICS. POPULATION DYNAMICS. SIZE DENSITY DISTRIBUTION GENDER RATIO AGE STRUCTURE BIRTH/ DEATH RATES. GENDER RATIO. For a monogamous species, like humans, the ideal sex ratio for a healthy population is 1:1 M:F. Monogamous behavior is rare in the animal kingdom.
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POPULATION DYNAMICS • SIZE • DENSITY • DISTRIBUTION • GENDER RATIO • AGE STRUCTURE • BIRTH/ DEATH RATES
GENDER RATIO • For a monogamous species, like humans, the ideal sex ratio for a healthy population is 1:1 M:F. • Monogamous behavior is rare in the animal kingdom. • Drop in worldwide amphibian populations. • Tied to unbalanced M:F ratios • Males converted to females! • “Estrogenic” chemicals. • http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=173544&fed_org_id=770&SIType=PR&TIMSType=&showCriteria=0&address=nerl/pubs.html&view=citation&personID=496&role=Author&sortBy=pubDateYear&count=100&dateBeginPublishedPresented= • http://1.usa.gov/1ao54Be
AGE STRUCTURE • The age structure of a population is important to the long-term success of that population, in that age structure is related to reproductive success. • For most species, older, and larger, individuals are more reproductively active. • Eg., an older and larger tree produces more seeds • Eg.,, an older and larger female fish produces more eggs
AGE STRUCTURE • Humans are unusual. • We generally outlive our reproductive years. • An older, or aging, human population is generally a declining population.
BIRTH AND DEATH RATES • DRs are, like reproductive rates, age sensitive. • Humans: • Follow 1,000 10-year olds • Follow 1,000 80-year olds • Track # individuals who die at end of year • Thus, aging human population will decline due to both reproductive factor and DRs.
BIRTH AND DEATH RATES • Larger animals tend to have lower BRs • Lower juvenile mortality • Eg., primates, marine mammals • Smaller animals, high BRs • High juvenile mortality • Eg., frogs
SURVIVORSHIP CURVES • Likelihood of survival with age.
DEMOGRAPHERS • Scientists who study population change.
EXPONENTIAL POPULATION GROWTH • Exponential growth only in early stages of population dynamics. • Only during “unregulated” growth. • No push-back from environment • Unlimited resources • Unlimited space • No natural predators • INVASIVE SPECIES!....Chap 4 ENDED 1/15
LIMITING FACTORS ARE THE “BRAKE” TO EXPONENTIAL GROWTH • Limiting factors are part of the overall evolutionary plan. • Otherwise....one species would blanket the Earth!
LIMITING FACTORS • PHYSICAL PARAMETERS • CHEMICAL • BIOLOGICAL • Together, these determine a population’s carrying capacity, the maximum population that a particular environment can sustain. • J-curve (exponential) -------- S-curve (logistic)
THEORETICAL LOGISTIC GROWTH CURVE Many Factors
CARRYING CAPACITIES CAN CHANGE • Eg., forest fire • CC for most animals decreases • CC for some plants, fungi, detritivores increase
DIFFERENT REPRODUCTIVE STRATEGIES • K-Selected species • r-Selected species
DIFFERENT REPRODUCTIVE STRATEGIES • K-Selected species • Low biotic potential • Larger animals • Invest energy/time in producing low numbers of high-quality offspring • Most competitive individuals selected by environment • High juvenile survivor rates • Giraffes, elephants, humans...
DIFFERENT REPRODUCTIVE STRATEGIES • r-Selected species • High biotic potential • Smaller animals • Invest little energy/time in producing high numbers of very similar offspring • Survival left to chance • Low juvenile survivor rates • Fish, plants, frogs, insects......
