Chapter 6 POPULATION BIOLOGY

OUTLINE DYNAMICS OF POPULATION GROWTH FACTORS THAT INCREASE OR DECREASE POPULATIONS FACTORS THAT REGULATE POPULATION GROWTH CONSERVATION BIOLOGY

OPTION 1 = $_______________________

BIOTIC POTENTIAL BIOTIC POTENTIAL refers to unrestrained biological reproduction. Biological organisms can produce enormous numbers of offspring if their reproduction is unrestrained. ENVIRONMENTAL RESISTANCE refers to the total of all factors that limit population growth. These are also known as LIMITING FACTORS As population increases so does environmental resistance!!

DYNAMICS OF POPULATION GROWTH POPULATION - all the members of a single species living in a specific area at the same time EXPONENTIAL GROWTH - growth at a constant rate of increase per unit time; has no limit dN/dt = rN The change in the Number of individuals (dN) per change in time (dt) equals the rate of growth (r) times the number of individuals in the population (N). r is often called the INTRINSIC CAPACITY FOR INCREASE.

EXPONENTIAL GROWTH Number of individuals added to a population at the beginning of exponential growth is relatively small. But numbers increase quickly because a % increase leads to a much larger increase as the population grows. J CURVE when the equation is graphed Exponential growth is a simple, idealized model. In the real world there are limits to growth.

EXPONENTIAL GROWTH

***RULE OF 70 YOU MUST KNOW THIS RULE OF 70 is used to determine the approximate doubling time of a population Doubling Time = 70 % growth rate 1. If a country was doubling its population every 35 years what would its growth rate be? 2. Currently, human pop growth rate is 1.2% In what year do you predict the world population will have doubled? DT = 70/r 35 = 70/r r = 70/35 r = 2% DT = 70/1.3 DT = 58 years 2017 + 54 = 2075

CARRYING CAPACITY CARRYING CAPACITY - limit of sustainability that an environment has in relation to the size of a species population OVERSHOOT - population exceeds the carrying capacity of the environment and death rates rise as resources become scarce POPULATION CRASH - growth becomes negative and the population decreases suddenly BOOM AND BUST - population undergoes repeated cycles of overshooting followed by crashing Oscillating Cycles of growth and decline

BOOM & BUST OR J CURVE Why does carrying capacity go down over time? Degradation of habitat over time Sometimes referred to Irruptive growth / Malthusian Growth Aside from dying – what else might individuals do in response to overshoot? Migrate, spread to new areas

GROWTH TO A STABLE POPULATION LOGISTIC GROWTH - growth rates regulated by internal and external factors until coming into equilibrium with environmental resources dN/dt = r N (1 - N/K) Terms have the same definitions as previous slide, with K added to indicate carrying capacity. Growth rate slows as population approaches carrying capacity. S CURVE when the equation is graphed

LOGISTIC GROWTH CURVE OR S CURVE Population grows rapidly BUT slows as it nears CC

J vs S POPULATION CURVES

r AND K SELECTED SPECIES r SELECTED SPECIES rely upon a high reproductive rate to overcome the high mortality of offspring with little/no parental care. ie: A clam releases a million eggs in a lifetime but the larva are so small that few survive. K SELECTED SPECIES have few offspring but more parental care so most young survive. ie: An elephant reproduces every 4 or 5 years.

REPRODUCTIVE STRATEGIES r-selected species 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. K-selected species 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. r – weeds, insects, mice, herbaceous plants, K – whales, apes, trees, top carnivores, elephant, bald eagle

FACTORS AFFECTING POPULATION GROWTH EXTERNAL FACTORS include habitat quality, food availability and interaction with other organisms. INTERNAL FACTORS include physiological stress due to overcrowding, maturity, body size, and hormonal status. These factors are DENSITY DEPENDENT, meaning as population size increases the effect intensifies. DENSITY INDEPENDENT effects (drought, an early frost, flooding, landslides, etc.) also may decrease population size.

FACTORS THAT INCREASE POPULATION NATALITY – birth rate FECUNDITY - physical ability to reproduce FERTILITY - measure of actual number of offspring produced IMMIGRATION - organisms introduced into new ecosystems Dispersal of organisms by wind or water currents over long distances. Sometimes carried by animals or on rafts of drifting vegetation.

FACTORS THAT DECREASE POPULATION EMIGRATION – individuals leaving an area MORTALITY - death rate SURVIVORSHIP - percentage of cohort surviving to a certain age LIFE EXPECTANCY - probable number of years of survival for an individual of a given age Increases as humans age. By older age, most individuals destined to die early have already done so. Has risen in nations/areas with good nutrition, sanitation and medical care Women live longer than men.

LIFE SPAN LIFE SPAN - longest period of life reached by a given type of organism Bristlecone pine lives 4,600 years. Human maximum lifespan is 120 years. Microbes may live a few hours. Differences in relative longevity among species are shown as survivorship curves.

SURVIVORSHIP CURVES FOUR GENERAL PATTERNS: (NOTE THE #’s) I. Full physiological life span if organism survives childhood Example: top consumers, Humans II. Probability of death unrelated to age Example: Sea gull, rodents IV. Mortality peaks both early and late in life. Example: Deer, crabs III. Mortality peaks early in life. Example: oysters, sea turtles, oak tree

SURVIVORSHIP CURVES Is known as TYPE I – “late-loss” curve – K strategists Is known as TYPE II – “constant loss” curve Is known as TYPE IV - Is known as TYPE III – “early-loss” curve – r-strategists

FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE DENSITY DEPENDENT FACTORS Have more influence as the population density increases They slow population growth Impact large % of population Disease, competition, predation, stress and stress related issues – aggression, decreased fertility and immunity, pathological behaviors due to high density Behaviors – locusts in swarms, lemmings,

FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE DENSITY INDEPENDENT FACTORS Not influenced by the size of the population All organisms are affected equally regardless of population density Fire, floods, weather, natural disasters, human-caused habitat disruption, etc.

FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE INTRINSIC FACTORS - operate within or between individual organisms in the same species competition, territoriality, stress, etc EXTRINSIC FACTORS - imposed from outside the population predation, climate, natural disasters, etc.

FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE ABIOTIC FACTORS - Caused by non-living environmental components. Tend to be density independent, and do not really regulate population although they may be important in increasing or decreasing numbers. ie: climate, weather, natural disasters, fire BIOTIC FACTORS - Caused by living organisms. Tend to be density dependent. They regulate population size by decreasing natality or increasing mortality.

DENSITY DEPENDENT FACTORS (biotic factors) INTERSPECIFIC INTERACTIONS (between different species) predator/prey, mutualism, commensalism, etc Resource partitioning, invasives, etc Predator-Prey Oscillating Cycles

DENSITY DEPENDENT FACTORS (biotic factors) INTRASPECIFIC INTERACTIONS - competition for resources by individuals within a population As population density approaches the carrying capacity, resources become limited. Control of access to resources by territoriality; owners of territory defend it and its resources against rivals. STRESS-RELATED DISEASES occur in some species when conditions become overcrowded. DISEASES – tend to spread faster with a higher population density

CONSERVATION BIOLOGY Critical question in conservation biology is the minimum population size of a species required for long term viability. SPECIAL CASE OF ISLANDS ISLAND BIOGEOGRAPHY MacArthur and Wilson proposed that species diversity is a balance between colonization and extinction rates. Small islands vs Large islands Far from mainland vs closer to mainland

CONSERVATION GENETICS In a large population, genetic diversity tends to be preserved. A loss/gain of a few individuals has little effect on the total gene pool. However, in small populations small events can have large effects on the gene pool. GENETIC DRIFT Change in gene frequency due to a random event FOUNDER EFFECT Few individuals start a new population.

CONSERVATION GENETICS DEMOGRAPHIC BOTTLENECK - just a few members of a species survive a catastrophic event such as a natural disaster Founder effects and demographic bottlenecks reduce genetic diversity. There also may be INBREEDING due to small population size. Inbreeding may lead to the expression of recessive genes that have a harmful effect on the population.

GENETIC DRIFT

POPULATION VIABILITY ANALYSIS MINIMUM VIABLE POPULATION is the minimum population size required for long-term survival of a species. ie: The number of grizzly bears in North America dropped from 100,000 in 1800 to 1,200 now. The animal’s range is just 1% of what is once was and the population is fragmented into 6 separate groups. Biologists need to know how small the bear groups can be and still be viable in order to save the grizzly.

METAPOPULATIONS METAPOPULATION - a collection of populations that have regular or intermittent gene flow between geographically separate units SOURCE HABITAT - Birth rates are higher than death rates. Surplus individuals can migrate to new locations. SINK HABITAT - Birth rates are less than death rates and the species would disappear if not replenished from a source.

METAPOPULATION