Population Dynamics: Factors Affecting Density and Population Growth in Ecology - Prof. Ro, Study notes of Biology

Download Population Dynamics: Factors Affecting Density and Population Growth in Ecology - Prof. Ro and more Study notes Biology in PDF only on Docsity! 1 • POPULATION SIZE • REGULATION OF POPULATIONS • POPULATION GROWTH RATES • SPECIES INTERACTIONS • DENSITY = NUMBER OF INDIVIDUALS PER UNIT AREA OR VOLUME • POPULATION GROWTH = CHANGE IN DENSITY OVER TIME FOUR (4) FACTORS AFFECTING DENSITY NATALITY (+) MORTALITY (-) IMMIGRATION (+) EMIGRATION FOUR (4) FACTORS AFFECTING DENSITY • IMMIGRATION • EMIGRATION –ASSUME THESE TWO ARE EQUAL DENSITY FUNCTIONS (CONT’D) • NATALITY: PROCESS OF ADDING NEW INDIVIDUALS TO POPUL. VIA BIRTHS –FERTILITY = PERFORMANCE (ACTUAL?) BASED ON NUMBERS BORN (HUMANS) –FECUNDITY = POTENTIAL LEVEL OF PERFORMANCE BASED UPON MEAN GESTATION TIME (HUMAN POPUL.) DENSITY FACTORS (CONT’D) • MORTALITY: DECREASE IN NUMBER OF INDIVIDUALS BY DEATH RATE – PHYSIOLOGICAL LONGEVITY = MEAN LIFE SPAN UNDER OPTIMUM CONDITIONS • SENESCENCE DEATH = OLD AGE – ECOLOGICAL LONGEVITY = EMPERICAL MEAN LIFE SPAN UNDER ANY GIVEN CONDITIONS 2 DENSITY MEASUREMENTS • ABSOLUTE DENSITY: TOTAL COUNTS (DIFFICULT/SOME ERROR) –HUMAN POPULATION CENSUS –BIRDS: ALL SINGING MALES INAREA –LARGE PLANTS IN GIVEN AREA (TREES) DENSITY MEASUREMENTS (CONT’D) • DENSITY ESTIMATES – USE OF QUADRATS (PLANTS, SMALL ANIMALS) – CAPTURE-RECAPTURE (MOBILE POPUL) • CLOSED: NOT CHANGE SIZE DURING SAMPLE PERIOD • OPEN: CHANGES IN SIZE DURING SAMPLE PERIOD • NOTE: REAL POPULATIONS ARE OPEN DENSITY ESTIMATES (CONT’D) • PETERSON INDEX: PROPORTIONAL COMPUTATION OF MARKED VS. UNMARKED INDIVIDUALS IN SAMPLE MARKED IND. = MARKED IN TOT. POPUL. TOTAL CAUGHT = TOTAL POPUL. SIZE POPULATION GROWTH • RATE OF GROWTH: CHANGE IN NUMBERS PER UNIT TIME • EXPONENTIAL GROWTH (UNRESTRICTED ENVIRONMENT) – FUNCTION OF TWO (2) FACTORS • SIZE OF POPULATION AT TIME ZERO • CAPACITY OF POPULATION TO INCREASE (I.E., BIOTIC POTENTIAL) OR DECREASE IN SIZE OVER TIME r = b - d INNATE CAPACITY FOR NATURAL INCREASE • NET REPRODUCTION PER INDIVIDUAL PER UNIT OF TIME (r) = (BIRTH RATE PER INDIVIDUAL PER UNIT OF TIME) - (DEATH RATE PER INDIVIDUAL PER UNIT OF TIME) CHARACTERIZES J-SHAPED CURVE EXPONENTIAL GROWTH N t +1 = r * N t 5 ASSUMPTIONS • UNREALISTIC--BUT GOOD BEGINNING POINT FOR CONSIDERATION OF POPULATION MODELS • BIOTIC POTENTIAL DOES NOT REMAIN CONSTANT IN NATURE • ATTEMPTS TO MEASURE IN NATURE NOT SIMPLE • r VARIES WITH ENVIRONMENTAL CONDITIONS, AGE DIST., GENETIC COMPOSITION, SOCIAL STRUCTURE, ETC.. S-SHAPED GROWTH CURVE LOGISTIC GROWTH =K dN/dt = r*N(K-N/K) K = MAXIMUM NUMBER OF INDIVIDUALS THAT CAN BE SUPPORTED BY THE ENVIRONMENT AT THAT TIME dN/dt = r*N LOGISTIC GROWTH: dN/dt = r*N(K-N/K) • K = CARRYING CAPACITY – MAXIMUM NUMBER OF INDIVIDUALS THAT CAN BE SUPPORTED (INDEFINITELY--ASSUMING EVERYTHING REMAINS THE SAME) INA GIVEN AREA (ENVIRONMENT) LOGISTIC GROWTH: dN/dt = r*N(K-N/K) • (K-N/K) IS A MEASURE OF ENVIRONMENTAL RESISTANCE – DIRECT EFFECT OF CROWDING • REPRESENTS AN INVERSE MEASURE OF ENVIRONMENTAL RESISTANCE – WHEN ENVIR. RESIST. IS LOW, VALUE OF (K-N/K) APPROACHES VALUE OF 1 • VARIOUS FACTORS AFFECT K – ANYTHING WHICH AFFECTS BIRTH RATE OR DEATH RATE WILL IMPACT K REGULATION OF POPULATION SIZE & RATE OF CHANGE • DENSITY DEPENDENT FACTORS –CROWDING EFFECT • DENSITY INDEPENDENT FACTORS –OTHER ENVIRONMENTAL RESISTANCE FACTORS • CARRYING CAPACITY EFFECTS –LOGISTIC GROWTH 6 DENSITY DEPENDENT FACTORS • INTRINSIC-- – POPULATION SIZE FACTORS • EXTRINSIC--INTERACTIONS WITH OTHER PARTS OF COMMUNITY STRUCTURE – PREDATION – PARASITISM – DISEASE – STRESS (TERRITORIALITY – INTRA & INTERSPECIFIC COMPETITION DENSITY INDEPENDENT FACTORS • MANY CATASTOPHIC EVENTS – OFTEN WEATHER RELATED • MODIFICATION OF WEATHER CONDITIONS (REGIONAL?) • FOOD QUALITY/QUANTITY • NUTRIENT TYPE – QUALITY & QUANTITY • HABITAT SELECTION EXPONENTIAL GROWTH CURVE HUMAN POPULATION AGE CLASS DISTRIBRUTION HUMAN POPULATION SPECIES INTERACTIONS • SPACING PATTERNS – RANDOM – CLUMPED (AGGREGATION) – EVENLY SPACED--REGULAR-- (HYPERDISPERSION) • EVALUATE TYPE OF DISPERSION (DISTRIBUTION) BY POISSON STATISTICS SPECIES DISTRIBUTION PATTERNS 7 SPECIES INTERACTIONS • SPACING (PATTERNS OF DISTRIBUTION) • PREDATOR-PREY INTERACTIONS • INTERSPECIFIC COMPETITION • EFFECTIVENESS OF COMPETITION • LOTKA-VOLTERRA MODELS TWO SPECIES INTERACTIONS • PREDATOR-PREY INTERACTIONS – TIME LAGS • COMPETITIVE INTERACTIONS • INTRERSPECIFIC COMPETITION • OCCURS WITH SYMPATRIC DISTRIBUTION OF TWO/MORE SPECIES IN SAME AREA PREDATOR-PREY INTERACTIONS • TIME LAG EFFECTS • ARRAY OF FACTORS AFFECTING EACH SPECIES IN QUESTION INDEPENDENT OF DIRECT INTERSPECIFIC COMPETITION INTERSPECIFIC COMPETITION • WILL OCCUR WITH SYMPATRIC DISTRIBUTION OF TWO OR MORE SPECIES • DEGREE OF INTERACTION (SEPARATION) MAY BE DEFINED WITH RESPECT TO SPECIFIC RESOURCES – FOOD SIZE PREFERENCE EFFECTIVENESS OF COMPETTION • ABILITY OF ONE SPECIES TO UTILIZE AVAILABLE RESOURCES THAN THE OTHER – KEY LIMITING RESOURCES, OR MANY OTHERS • FUNCTION OF ENVIRONMENTAL CONDITIONS • GENETIC/SOCIAL STRUCTURE FACTORS • SUPPORTED BY LAB STUDIES • TEMP VARIATION, HUMIDITY, FOOD QUAL & QUANTITY, ACCUM. WASTE PRODUCTS COMPETITIVE EXCLUSION • GAUSE: • NO TWO (2) SPECIES CAN EXIST (SURVIVE) ON SAME LIMITING RESOURCES…AT SAME TIME ALL OF THE TIME • SPECIES WITH IDENTICAL RESOURCE REQUIREMENTS CANNOT CO-EXIST • CONCEPT OF NICHE, NICHE OVERLAP