Chapter 6 Population Biology

Births

B the number of births that occur in the population at any given time; rate of births vary by species and also with stress and food availability

J-shaped curve

Exponential growth, where a population grows exponentially until it overshoots the carrying capacity, a dieback occurs dropping the population below the carrying capacity and then exponential growth occurs again. This is an oscillating pattern.

logistic growth is what

Logistic growth is density-dependent which means that the growth rate depends on population density. Density-dependent factors intensify as population size increases. Density-independent factors may also affect populations

why is hunting important for population management

Prevents starvation, habitat abuse, and death Assures that there is plenty of food for the population so that each can reach their genetic potential

examples of density-independent factors

drought, fire, or other habitat destruction that affects an ecosystem

genetic drift

due to founder effect and bottleneck effect Founder effects and demographic bottlenecks reduce genetic diversity Each may also result in inbreeding due to small population size Inbreeding may lead to the expression of recessive genes that may have a deleterious effect on the population

founder effect

occurs when a few individuals start a new population

demographic bottleneck

occurs when just a few members of a species survive catastrophic event such as a natural disaster

intrinsic factors

operate within or between individual organisms in the same species

exponential growth

growth at a constant rate of increase per unit time (geometric); has no limit Exponential growth describes continuous change. Growth under ideal conditions occurs continuously. This modifies the formula to dN/dt = rN d = delta which represents change Exponential growth only can be maintained by a population as long as nothing limits its growth

K-selected species

have few offspring, slower growth as they near carrying capacity and exercise more parent care to ensure offspring make it to adulthood. Ex: elephants produce an offspring every 4-5 years. Longer lives, slower growth, late maturity, few, large offspring, adapted to a stable environment, niche specialists, predators, regulated mainly by intrinsic factors, high trophic levels

extrinsic factors

impose from outside the population

endemic

native to only one area

what did MacArthur and Wilson propose

proposed that species diversity is a balance between colonization and extinction rates

rate

r this is the rate of growth; the number of individuals which can be produced per unit of time under ideal conditions (no limits to populations growth)

4 factors that affect population growth rate are

r = B + I - D - E

population crash

rapid dieback in the population to a level below the carrying capacity

density-dependent factors

reduce population size by decreasing natality or increase mortality. Density-dependent factors include: Interspecific interactions between species such as the predator-prey oscillation Intraspecific interactions: competition for resources by individuals within a population. As population density approaches the carrying capacity, one or more resources become limiting. Control of access to resources by territoriality; owners of territory defend it and its resources against rivals Stress-related disease occurs in some species when conditions become overcrowded

what is carrying capacity

(K) the population of a species that can be supported in a specific area without depleting the available resources

islands are

endemic

Deaths

D mortality, or the number of deaths that occur in the population at any given time, vary by species and with environmental factors

Emigration

E the number of organisms that move out of the population to another population

why was the great elephant census important

Elephants are a keystone species and crucial to Africa's forests and savannas. They are vulnerable and creating a sustainable elephant population will require a coordinated and multifaceted effort. Census designed to provide accurate data about the number and distribution of African elephants by using standardized aerial surveys of tens of hundreds of thousands of square miles. The final results from the Great Elephant Census showed 352,271 African savanna elephants in 18 countries, down 30% in 7 years

population biology with bluefin tuna

Fisherman paid $10,000+ for one bluefin tuna at the dock which created an overfishing problem Ban of international trade of bluefin tuna Stronger management Steps were taken in 2016 to reduce illegally caught tuna 2017- the population is more stable

what are the 3 general patterns of survivorship curves

Full physiological life span if the organism survives childhood. Ex: elephants and bears. The curve starts high, remains stable, then decreases rapidly at the postreproductive period Probability of death unrelated to age. Ex: gulls and mice. The curve decreases in a linear fashion Mortality peaks early in life. Ex: trees and fish. The curve decrease rapidly during the dependency period then remains stable.

Immigration

I the number of organisms that move into the population from another population

conservation genetics

In a larger population, genetic diversity tends to be preserved. A loss/gain of a few individuals has little effect on the total gene pool A small population gene pool can be greatly affected by small events. This is evidenced by genetic drift which is a change in gene frequency due to random events

why is exponential growth not viable in the long run

In the real world, there are limits to growth that each population will encounter. Eventually, shortages of food or other resources lead to a reduction in the population size

population viability analysis

Minimum viable population is the minimum population size required for the long-term survival of a species

Population

N total number of all members of a single species living in a specific area at the same time

S-shaped curve

Sigmoidal growth curve or logistic growth, where a population grows exponentially until it nears the carrying capacity and the population growth slows as resources become more scarce. The population eventually levels out at a level below the carrying capacity

population biology with deer management

Too many deer means starvation, habitat abuse, and death Hunting helps with managing deer populations Wildlife biologists estimate deer populations to guide hunting regulations A regulated harvest helps assure that there is plenty of food for the number of animals present on the range. Balancing deer numbers with the amount of forage available ensures maximum body and antler growth in order for more animals to reach their genetic potential

Describe what happens if a population exceeds carrying capacity (use the terms overshoot, population crash, and boom and bust in your response)

When a population exceeds its carrying capacity it overshoots the resources available resulting in deaths from a scarcity of resources. This creates a population crash, where the population dieback far below the carrying capacity. When a population repeats this cycle of overshoot and crashing it is described as boom and bust which is an oscillation of population growth around the carrying capacity.

examples of density-dependent factors

disease, physiological stress, and predation

what factors add to a population

births and immigration

biotic factors

caused by living organisms. Tend to be density-dependent

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. Ex: rainfall, storms

conservation biology

critical question in conservation biology is the minimum population size of a rare species required for long term viability

what factors lower a population

deaths and emigration

R-selected species

rely upon a high reproductive rate to overcome the high mortality of offspring with little or no parental care. Ex: clams release millions of eggs with few surviving. Shorter lives, rapid growth, early maturity, many small offspring, adapted to unstable environment, niche generalists, prey, regulated mainly by extrinsic factors, low trophic levels

what does resource scarcity slow

slows exponential growth as the population is near the carrying capacity

island biogeography

small islands far from the mainland have fewer terrestrial species than larger, closer islands

time

t this is the unit of time upon which the rate is based

maximum life span

the longest period of life reached by a given type of organism. Differences in relative longevity among species are shown as survivorship curves Bristlecone pine = 4,600 years Humans = 120 years Microbes = few hours

geometric rate of increase

the population size that would occur after a certain amount of time under ideal conditions is described by the formula: Nt = Nor^t

overshoot

when a population exceeds the carrying capacity of the environment and deaths result from a scarcity of resources

boom and bust

when a population undergoes repeated cycles of overshoots followed by crashes