POPULATION DYNAMICS CARRYING CAPACITY CHAPTER 9 APES 12/2006

Figure 9-1 Page 190

Population Dispersion Fig. 9-2 p. 191

Factors Affecting Population Growth Births deaths immigration emigration

The Biotic Potential Population potential capacity to grow Intrinsic rate of increase(r ) - rate with unlimited resources reproductive age reproduce many times many offspring Two houseflies, ten years, several meters over entire earth - yuck :-(

Population Growth Rate Birth Rate: births/popn at beginning Death rate: deaths/popn at beginning Growth rate = birthrate-deathrate Example Population of 5000 on Jan 1 Births 400 throughout year Deaths 100 throughout year What is Birthrate and deathrate? How many added to this population this year Calculate number added if population were 100,000 at beginning of year instead of 5000 Answers: BR=8%; DR =2%; GR=6% Popn 100000 added is 6000

Rate of Growth – Births What would affect number of births in a population? Number of young in each “litter” Examples of high and low number?? How often have young Examples of seldom vs. often Age at which females start having young Rodents vs. elephants Biotic potential for a population

Rate of Growth – Deaths What would affect number of deaths in a population? Lifespan Outside environmental factors – limiting factors density dependent examples density independent

Environmental Resistance Limits population growth Population size - interplay between biotic potential and environmental resistance Carrying capacity (K) - number individuals of a given species that can be sustained - expressed as in a given area (say sq. m) Minimum viable population locate mates sufficient genetic diversity

© 2004 Brooks/Cole – Thomson Learning (environmental resistance) POPULATION SIZE © 2004 Brooks/Cole – Thomson Learning Growth factors (biotic potential) Decrease factors (environmental resistance) Abiotic Too much or too little light Temperature too high or too low Unfavorable chemical environment Abiotic Favorable light & temperature & food chemical environment (optimal level of critical factors) Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and and adapt to environmental change Low reproductive rate Specialized niche Changing food supply Too many competitors Insufficient ability to hide from or defend against predators Inability to migrate and live in other habitats Biotic Biotic

Exponential vs. Arithmetic Growth Arithmetic: constant amount per time unit Independent of population size Exponential: increases by constant fraction, or exponent, by which current population multiplied Dependent on population size Power of biological reproduction Compound interest

The J Curve

The Rule of Seventy At 1% per year, population doubles in 70 years (Table 6.1) Doubling time = 70 / % increase So, if 4% growth (interest) rate, what is doubling time?

Logistic Strategies Exponential or J-phase Followed by S-phase Do not overshoot carrying capacity As populations increases, birthrate decreases Intrinsic: Territoriality, decreased fertility Extrinsic: predators, parasites, resources - may overshoot, then return to carrying capacity

Logistic Growth

Carrying Capacity

Factors Regulating Population Growth Extrinsic vs. Intrinsic Biotic vs. Abiotic Density-Dependent vs. Density-Independent Interspecific: predation, parasitism, competition Intraspecific: Competition, territoriality Stress Related factors

Malthusias or Irruptive Growth May go through repeated cycles Early successional species Opportunists

Malthusian or Irruptive Growth Rapid exponential growth (J curve) followed by population crash Population surpasses carrying capacity Deathrate exceeds birthrate Thomas Malthus: human populations tend to grow until resources exhausted, death by famine, disease, war

Malthusian or Irruptive Growth

Moose and Wolves of Isle Royale

Isle Royale - Wolves and Moose What caused 1930 crash in moose popn.? Why did the moose not decrease their population before the crash occurred? Why did the predators not exterminate the moose population? What happened when the wolf population declined in the 1980s?

© 2004 Brooks/Cole – Thomson Learning Irregular Stable Number of individuals Cyclic Irruptive Figure 9-7 Page 194 Time

Few but large young, protect young, lower infant mortality K-Strategists Few but large young, protect young, lower infant mortality Long lifespan Later reproductive age Less energy on reproduction Later successional environments More specialized niches

R-Strategist Species Prolific reproduction, up unprotected young, high mortality rate of young Low in trophic levels Early succession Opportunists Populations regulated by extrinsic environmental effects Insects, parasites, algae, annual plants, many fish

Survivorship Curves Percent of population surviving at different ages

Deer in PA DCNR and State Forest Deer browsing studies

The Cats Dropped In ! What - cats parachuted into North Borneo? What lessons can be learned? What are the ecological connections? (“Ecological Surprises” - page 200)