Introduction to Ecology Chapters 52
Ecology • Ecology – the study of interactions between organisms and the environment • Biotic – living components of an ecosystem (ex. animals and plants) • Abiotic - nonliving components of an ecosystem (ex. soil, air, and water)
Species distribution • Interactions between organisms and the environment limit the distribution of species. • What affects the distribution of species? • Dispersal limits (range expansions and species transplants) • Behavior and habitat selections • Biotic factors (other species) • Abiotic factors (temperature, water, sunlight, wind, rocks/soil, and climate)
Figure 50.10 A climograph for some major kinds of ecosystems (biomes) in North America
POPULATION ECOLOGY CHAPTER 53
POPULATION CHARACTERISTICS • Population – organisms of the same species in the same area • Density – number of individuals in a given area (example: 1200/m2) • Dispersion – pattern of spacing among individuals
Measuring Size • Quadrant method used for stationary organisms • Mark and recapture used for mobile organisms
Patterns of Dispersion • Clumped – individuals aggregated in patches (most common) • Uniform – evenly spaced individuals • Random – unpredictable, patternless
DEMOGRAPHY • Demography is the study of factors that affect populations • Age structure – relative number of individuals of each age • Birthrate or fecundity – number of offspring born during a certain time period • Death rate – number of individuals who die in a certain time period • Generation time – average span between birth of individuals and the birth of their offspring • Sex ratio – proportion of individuals of each sex
Life tables – used to determine how long, on average, an individual of a given age could be expected to live • Cohort – group of individuals of same age • Survivorship curve – a plot of the numbers in a cohort that are alive at each age
Life Table for Belding Ground Squirrels (Spermophilus beldini) at Tioga Pass, in the Sierra Nevada Mountains of California
LIFE HISTORIES • Life history – traits that affect an organism’s schedule of reproduction and death • Life histories vary greatly • Salmon travel to ocean to mature and then back to stream to reproduce • Some oaks cannot reproduce until they are at least 20 years old • Semelparity or big bang reproduction – produce numerous offspring and then die • Iteroparity or repeated reproduction – produce fewer offspring over many seasons
There is a trade-off between reproduction and survival • Female red deer who are reproductive have a greater chance of dying • Larger brood sizes increase mortality rate
Cost of reproduction in female red deer on the Island of Rhum, in Scotland
Probability of survival over the following year for European kestrels after raising a modified brood
POPULATION GROWTH ΔN = Change in population size B = # births during time interval (birth rate) D = # deaths during time interval (death rate) Δt = time interval ΔN/Δt = B – D Per capita birthrate (b)= # offspring produced per time by an average member of population Ex. 46 births/year in pop of 1000 so b = 46/1000 = 0.046 Birth rate = Expected # births/year for pop (B): B=bN Ex. B = 0.046 x 500 = 23 births/year (where N = 500)
Per capita death rate (m)= # deaths per time by an average member of population Ex. 22 deaths/year in pop of 1000 so m = 22/1000 = 0.022 Death rate = Expected # deaths/year for pop (D): D=mN Ex. D = 0.022 x 500 = 11 deaths/year (where N = 500) Maximum per capita growth rate (rmax) ΔN/Δt = bN – mN (birthrate – death rate) r = b – m ΔN/Δt = rmaxN (exponential growth rate) dN/dt = rmaxN (calculus version)
If a population is growing, r is positive. • If a population is declining, r is negative. • Zero population growth occurs when r = 0 • Exponential growth – maximum population growth rate • Intrinsic rate of increase is the maximum population growth rate, rmax • Exponential growth is: • dN/dt = rmax N
Carrying capacity (K) – maximum population size that a particular environment can support with no net increase or decrease • Logistic Growth – incorporates the effect of population density on rmax, allowing it to vary from rmax under ideal conditions to zero as carrying capacity is reached.
When N is small compared to K, the per capita rate of increase is high. (N = pop size) • When N is large and resources are limiting, the per capita rate of increase is small. • When N = K, pop stops growing. • For logistic growth: ΔN/Δt = rmaxN(K-N/K)
How does the logistic curve fit real populations? • Some populations closely follow the S-shaped curve. • Other populations do not. • Low numbers may hurt a population (rhinos) • Populations may overshoot the carrying capacity and then drop below K.
Strategies • K-selected populations (density dependent) • organisms that are likely to be living at density near the limit imposed by the environment (K) • r-selected populations (density indepedent) • organisms that are likely to be living in variable environments in which populations fluctuate or in open habitats where individuals are likely to face little competition
POPULATION LIMITING FACTORS • Limiting factors – factors that limit population growth • Density dependent factors – death rate rises or birth rate falls with increasing pop density • Disease • Predation • Competition • Lack of food • Lack of space • Density independent – birth rate or death rate that does not change with pop density • Climate
Long-term study of the moose (Alces alces) population of Isle Royale, Michigan
Age-structure pyramids for the human population of Kenya (growing at 2.1% per year), the United States (growing at 0.6% per year), and Italy (zero growth) for 1995
Annual percent increase in global human pop (data from 2005). Sharp dip in 1960 due mainly to famine in China that killed 60 million people.
COMMUNITY ECOLOGY CHAPTER 54
COMMUNITIES • Communities – different populations living within the same area • What factors are most significant in structuring a community?