15. Chapter 53: Population Ecology Flashcards
Biological species concept
- species interbreed, cannot with other groups
2. difficult to apply in field b/c asexual, hybrids, fossils
How have most named species been ID?
morphological characters
Cryptic species and evolutionary significant units (ESU) may be indistinguishable. What would be useful to distinguish?
Genetics
How would a biologist ID populations?
- Determine (guess) gene flow b/w these pops.
2. separation often arbitrary
3 patterns of dispersion
- random: position of each individual is independent of others (uniform enviro but no pattern of attraction or avoidance - some forest trees)
- uniform: evenly spaced apart, a result of intraspecific competition
- clumps: result of habitat differences, reproductive necessity, offspring dispersal (most common)
Temporal dispersion
dispersed in time and space as a response to environmental conditions (food, light) or only clump during mating
Dispersal movements
immigrate (into) or emigrate (out) of population
migration (an example of dispersal movement)
dispersal with subsequent return to place of origin (enviro adaption to pressures)
Migratory examples (7)
- Zooplankton: lower by day and up at night
- Elk: high altitude in summer, low in winter
- Some caribou: calve in tundra, winter in taiga
- gray whales: food-rich arctic in summer, to winter
- Birds: long-range migrants (Arctic tern)
- Pacific salmon: one return trip as young and return home to spawn and die
- Monarch: fall migrants do not return north but offsprings do
Four factors of all populations
- Births
- Death
- Immigration
- Emigration.
Population growth equation
N (future) = N (present) + (B-D) + (I-E)
- lots of examples of exponential growth
What will halt pop growth?
competition: interaction b/w individuals lead to reduction in survivorship and/or reproduction
Define resource
anything that is essential for continuance of life and that is finite
Define limiting resource
the resource that is in the shortest supply in relation to organism’s demand for it (nest cavities, sodium) competition is for limited resources
Density dependent
effects of competition are likely to be greater as # of competitors increase (i.e mortality vs density graph - line remains straight until density increase then it goes up or down)
What is the primary pattern as density increases?
the per capita birth rate eventually decreases and per capita death rises
Patterns of density
- intersection pt where births = deaths = stable pop.
- if birth > death = pop. increase
- if death > bith = pop. decrease
What is the intersection density known as?
populations carrying capacity (K)
theoretically, all densities tend to approach K but more complex in wild b/c enviro unpredictable therefore K = range
Logistic growth
- growth followed by stabilization (s- shaped, sigmoidal) common as approaches K
- growth slows as density increases
(K = flattens out)
How is the behaviour of he pop. sensitive to rate of growth?
- high growth rates = oscillations
- very high growth rates = chaos
- accentuated by time lags, climatic variations, predator behaviour
How is the ratio of young to adults informative?
- increase pop. tend to have high young
- decrease pop. have few young
- deficiency in young lead to aging pop.
Examples of growth rates
- Kenya: bottom heavy, lots of young, rapid growth
- US: hourglass: more young than old, slow growth
- Italy: top heavy, more old than young, no growth, decline
What is organismal aging or senescence characterized by?
declining ability to respond to stress, homeostatic imbalance, + risk of disease
Ultimate consequence of aging
death (some gerontologist regard age as disease that may be curable)
Do we live longer now than in 1800?
No, we just don’t die as young (evolutionary biologist don’t think aging is curable)
Define life expectancy
average # of yrs to be lived in future by members of given age in pop.
Evolutionary explanation for aging?
grounded in idea that strength of natural selection decreases with age
(i.e. gene for heart attack at 15yrs, strongly selected against but if for 50yrs then weaker selection and genes may have already been past on to next generation)
Pleiotropic genes
genes that have more than one effect on phenotype
Antagonistically pleiotropic genes
those that have one beneficial effect and one deleterious effect (e.g. testosterone)
Why do humans live so long? No other primate has such an extended post-reproductive phase of life.
“grand-parenting theory” - humans teach young, evolutionary advantage to keep older survivors to teach and care for young
Let’s say you are studying a population of concern. Often you want to start by gathering basic demographic data. What would that include?
- pop. size/ density
- age of members
- sex ratio
- birth/death rates
(experimental error can accumulate at ea. step)
How id demographic ideally determined by?
tracking cohort from birth to death. Cohort is members of a pop. that are the same age
Define life history
the pattern of growth, reproduction and mortality for individual (or pop.)
Define Semelparous
produce offspring in a single reproductive event (i.e. Pacific salmon)
Define Iteroperous
produce offspring in series of multiple reproductive events
What do life tables allow ecologists to make comparisions between?
sexes, cohorts, populations and species
Survivorship curves
shows apparent patterns despite great variety in life histories
(i.e. pattern in relationship b/w mortality and fecunity) Natural selection cannot max. all variable simultaneously - life history trade-offs
What are the three hypothetical types of survivorship curves classified as in order to compare to real-life data?
- Type I curve: high survivorship throughout life then experience heavy mortality in old age (e.g. many mammals)
- Type II curve is linear: pop. with constant mortality rates (e.g. adult stages of birds)
- Type III curve is conclave: typical in pop. with high mortality in early life (e.g. fish, invertebrates, some plants)
