Population Growth Flashcards
Desert biome
Occurs near 30 degrees north and south of the equator and in the interiors of continents; dry, extreme, low biodiversity
Climate:
-may be hot or cold
-temps. can be extreme and vary greatly from day to night and seasonally
-precipitation is low and highly variable, generally less than 30 cm per year
Biodiversity:
-plants and animals occur in low densities and must be adapted for desiccation tolerance and low nutrient availability; low primary productivity
-low but variable biodiversity
Savanna biome
Occurs in equatorial and subequatorial regions; dry, warm, moderate biodiversity
Climate:
-precipitation is seasonal w/ a prolonged dry season
-temps. are warm and more seasonally variable than in tropical forests
Biodiversity:
-plants (grasses, forbs, trees) are fire-adapted and tolerant of seasonal drought; moderate primary productivity
-moderate biodiversity
-spread of trees constrained by periodic fires (disturbance)
Temperate grassland biome
Most extensive in central North America (prairie) and Asia (steppes); dry, seasonal, moderate biodiversity
Climate:
-precipitation is low and seasonal, occurring mainly in summer
-winters are cold, summers are hot
Biodiversity:
-dominant plants are herbaceous (grasses and forbs); moderate primary productivity
-moderate biodiversity
-dominant plants are adapted to droughts and fire (disturbance)
Northern Coniferous Forest biome
Spans northern North America and Eurasia and is the largest terrestrial biome on Earth; mixed rain, cool, low biodiversity
Climate:
-precipitation varies; some have periodic droughts and others, especially near coasts, are wet
-winters are cold, summers may be hot
Biodiversity:
-dominated by conifers such as pine, spruce, fir, and hemlock; low primary productivity
-low biodiversity
-some species depend on periodic fires to regenerate (disturbance)
Unregulated growth
biotic and abiotic factors affect population demographics; geometric and exponential models describe population growth in an idealized, unlimited environment
Regulated growth
logistic population growth models incorporate carrying capacity (K), such that population growth approaches zero as the population size nears K; density dependent factors regulate population growth; life history traits fall into two general reproductive strategies
Demography
study of population vital statistic and how they vary w/ age
Life table
age-specific summary of the vital statistics of a population
Cohort
a group of individuals in a population born about the same time
Survivorship (lx)
proportion of individuals born that survive from one age group to the next (like a percentage or decimal)
Type 1 survivorship curve
low death rates during early and middle life and a sharp increase in death rates later in life; found in large mammals (for example, humans and elephants) that produce few offspring but provide them w/ good care
Type 2 survivorship curve
constant death rate over the life span; found in some rodents, invertebrates, lizards, and annual plants
Type 3 survivorship curve
high death rates for the young; death rate steeply declines for survivors of early period die-off; found in organisms that produce very large numbers of offspring but provide little or no care (for example, long-lived plants, many fishes, and most marine invertebrates)
Reproductive table
age-specific summary of the reproductive rates in a population; w/ separate sexes only females are recorded
Geometric growth
unregulated population growth in discrete time intervals; Ex: Giardia intestinalis growth by binary fission every 12 hrs
Exponential growth
unregulated population growth in continuous time intervals; Ex: humans
Change in population size
Births + immigration - death - emigration
Population growth rate
N/t = B - D
net reproductive rate (R)
the difference between # of births and # of deaths that occur in the time interval
Per capita (per individual) change in population size (r x delta t)
average contribution each individual makes to the population size during the time interval
What is the per capita change in population size for a population of 1,000 individuals that increases by 16 individuals per year?
16/1000 = 0.016
R = r x delta t x N
used to calculate how many individuals will be added to a population each year
R = r x delta t x N. If the per capita change in population size is 1.5 and the population is currently 100 individuals, how many individuals will be added to the population in the next generation?
1.5 x 100 = 150
dN/dt = rN
rate of change at each instant in time; dN/dt represents very small changes in population size over short time intervals: exponential population growth where r is the intrinsic rate of increase, the per capita rate at which an exponentially growing population increases in size at each instant in time
Why does unregulated population growth happen?
When a population is introduced to a new environment, when a population is rebounding after a drastic reduction by a catastrophic event or experiencing an influx of new nutrients; Ex: elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned
Why can’t populations grow geometrically or exponentially for long?
Increasing population size results in:
-shortages in food and other limiting resources
-greater intraspecific aggression
-increased attention from predators
-greater risk of disease outbreaks
When the per capita rate of increase is positive and constant, the number of individuals added to the population ___ through time
increases
