biology chapter two Flashcards
Population size and Density
Ecologist use quantitive measurements to study and describe populations
Population size
the number of species living within a specific geographical area
Population density (dp)
the number of individuals per unit of volume or area
Sampling techniques
counting each individual of a species would be difficult due to factors such as time, money and human resources
- instead ecologist’s use subsets or larger populations in order to make estimates
3 types of techniques used to estimate population size N and density Dp
- Transcets
- Quadrates
- Mark recapture
Transcets
a long and narrow rectangular area or line used for sampling a population
Quadrats
an area of a specific size used for sampling a population
- this method is usually used to sample immobile organisms or those that move very little
Mark recapture
a method in which animals are captured and marked with a tag, collar or band
3 types of population distrubution
- Uniform
- Random
- Clumped
Uniform
resources are evenly distributed but scarce as they often have a consequence of negative interactions among population members such as competition for resources
Random
Resources are abundant and uniformly distributed across an area, there is no competition for resources in these areas
Clumped
resources are unevenly distributed, so populations tend to gather around them, this is a typical pattern in nature
- clumped distribution is usually the result of positive interactions such as co- cooperative feeding
Life histories
Ecologists use life histories to aid in understanding populations and they use quantitative measures of vital statistics to determine population size
- two primary measures used to describe life history are Fecundity and survivorship
Fecundity
the average number of offspring produced by a female member of a population over her lifetime
Fecundity and Biotic potential
Biotic Potential occurs with ideal population growth conditions
-BP is the highest possible per capita growth of a population (When limiting factors aren’t present)
the factors that determine a species’ BP
- Age of reproductive matter
- how often reproduction can occur
- number of offspring per reproductive cycle
- number of offspring that survive to reproduce
- lifespan of individuals
Survivorship
The number of percentage of organisms that typically live to a given age in a given population
- there are three types of survivorship and they can be displaced on survivorship curves
type one: High rate of survival
Type two: Moderate rate of survival
type two: Low rate of survival
Demography
population are dynamic and four factors are used to determine population growth rates
- Births (b)
- Deaths (d) (Mortality)
- Immigration (i)
- Emigration (e)
Population growth models
the two main population growth models
- Exponential (J- curve)
- Logistic (S- Curve)
Exponential growth (J- shaped curve)
type of curve exhibited by population at its biotic potential
- the population grows faster and faster as it gets larger
- example bacteria in a petri dish
Logistic growth
type of curve exhibited by population that cannot grow at its biotic potential because resources are limited
- the population reaches it’s carrying capacity - the maximum population size that a habitat can support overtime
Limiting factors
Density- dependant factors
Density- independent factors
Density Dependant
DD factors are Biotic limiting factors and include:
= Limited resources
= competition
= predation
= parasitism
Density Independent
DI factors are Abiotic limiting factors and include:
- weather
- natural resources
