Chapter 8 Population Ecology

WHAT IS A KEYSTONE? THE TOP BLOCK IN AN ARCHWAY REMOVE KEYSTONE ARCHWAY COLLAPSES

KEYSTONE SPECIES PLAY CRITICAL ECOLOGICAL ROLE IN HELPING SUSTAIN A COMMMUNITY EX. POLLINATORS, TOP PREDATORS (WOLF, LEOPARD, LION, ALLIGATOR, SOME SHARKS) DUNG BEETLES, SEA STARS, SOUTHERN SEA OTTER

KEYSTONE SPECIES LOSS OF KEYSTONE SPECIES CAN LEAD TO POPULATION CRASHES AND EXTINCTION OF OTHER SPECIES IN COMMUNITY THAT DEPENDS ON THE K.SPECIES FOR CERTAIN SERVICES/ROLES;

POPULATION DYNAMICS AND CARRYING CAPACITY 3 Types of Population dispersal: 1) Clumped 2) Uniform 3) Random Figure 8-2

THE WORLD IS MOSTLY CLUMPY HERDS, FLOCKS, SCHOOLS, PACKS RESOURCES SPECIES NEEDS VARIES GREATLY IN AVAILABILITY FROM PLACE TO PLACE; CAN PROVIDE BETTER PROTECTION FROM PREDATORS & POPULATION DECLINE BETTER CHANCE FOR FOOD, MATING & CARING FOR YOUNG

POPULATION DYNAMICS MOSTLY REPRODUCTIVE AGE – POPULATION INCREASE MOSTLY POSTREPRODUCTIVE AGE – POPULATION DECREASE EVEN DISTRIBUTION PRE & POST – POPULATION IS STABLE NO POPULATION CAN INCREASE ITS SIZE INDEFINITELY

Population Dynamics Depends on: size, density, dispersion, age distribution Biotic potential = capacity for growth Intrinsic rate of increase (r) – rate population grows if resources unlimited High r 1) reproduce early, 2) short generation times, 3) long reproductive life, & 4) have many offspring Carrying capacity (k) – Biotic potential + environmental resistance Limiting Factors – light, water, space, nutrients, competition, predators, disease (environmental resistance)

CARRYING CAPACITY (K) THE MAXIMUM POPULATION OF A GIVEN SPECIES THAT A PARTICULAR HABITAT CAN SUSTAIN INDEFINITELY WITHOUT DEGRADING THE HABITAT GROWTH RATE DECREASES AS POPULATION SIZE NEARS K

Changes in Population Size: Entrances and Exits Rule of 70: To calculate doubling time for a population in years, divide 70 by the percent growth rate

Age Structure: Young Populations Can Grow Fast How fast a population grows or declines depends on its age structure. Prereproductive age: not mature enough to reproduce. Reproductive age: those capable of reproduction. Postreproductive age: those too old to reproduce.

Biotic Potential vs. Environmental Resistance No population can increase its size indefinitely. Intrinsic rate of increase (r) -rate at which a population would grow if it had unlimited resources (biotic potential). Carrying capacity (K): maximum population of a given species that a particular habitat can sustain

Exponential and Logistic Population Growth: J-Curves and S-Curves J-curve: exponential growth S-curve: logistic growth Figure 8-4

POPULATION GROWTH NO OR FEW RESOURCE LIMITATIONS POPULATION WILL GROW AT A FIXED RATE OF 1% TO 2% EACH YEAR

EXPONENTIAL GROWTH GEOMETRIC STARTS SLOWLY THEN ACCELERATES AS POPULATION INCREASES DUE TO BASE SIZE OF POPULATION INCREASING FIGURE 8-3 BOTTOM HALF

LOGISTIC GROWTH S-CURVE: RAPID EXPONENTIAL GROWTH FOLLOWED BY STEADY DECREASE IN POPULATION GROWTH WITH TIME UNTIL POPULATION GROWTH LEVELS OFF FIGURE 8-3 WHOLE CURVE

Exceeding Carrying Capacity: Density-independent factors: ctrl size without consideration of population size – natural disasters Density-dependent factors: do depend on population size – competition, space, predation, disease, parasitism Figure 8-6

Types of Population Change Curves in Nature Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. Stable: fluctuates slightly above and below carrying capacity. Irruptive: populations explode and then crash to a more stable level. Cyclic: populations fluctuate in regular cyclic or boom-and-bust cycles. Irregular: erratic changes possibly due to chaos or drastic change.

Types of Population Change Curves in Nature Predator-prey cycles – top-down vs. bottom-up control Figure 8-7

REPRODUCTIVE PATTERNS Some species reproduce without having sex (asexual). Offspring are exact genetic copies (clones). Others reproduce by having sex (sexual). Genetic material is mixture of two individuals. Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly. Major advantages: genetic diversity, offspring protection.

Reproductive Patterns: Opportunists and Competitors r-strategists - Large number of smaller offspring with little parental care K-strategists - fewer, larger offspring with higher invested parental care Figure 8-9

Reproductive Patterns r-selected species tend to be opportunists while K-selected species tend to be competitors. Figure 8-10

Survivorship Curves: Short to Long Lives Late loss: live to old age Constant loss: die at all ages (birds, lizards, small mammals) Early loss: die at young ages Figure 8-11