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What is population density?
The number of individuals per unit of volume or area.
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How can ecologists determine population density?
By counting the number of individuals in a smaller sample and making an average.
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What are transects?
samples taken along a long rectangle or line. Researcher chooses a random starting point and walks the length counting the species. (Useful when density is low or organisms are large)
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What are quadrats?
An area of specific size used for sampling, multiple quadrats may be placed. (Useful for sessile animals)
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What is the formula for finding density in a quadrat? How can we extrapolate this information?
Dp=N (sum of individuals)/ A (size of quadrat)
Estimated density x total area
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How can we determine relative density?
Indirect factors such as feces and tracks can help determine the relative density, which is an estimate compared to the absolute density.
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What is mark recapture?
Animals are captured, marked then released. They are then retrapped and scientists compare the number of mark to the number of unmarked.
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What is the formula used when analyzing mark recapture?
N (population size) = (# originally marked x total in recapture)/ marked in recapture
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What is a distribution pattern?
The pattern in which a population is distributed or spread in an area. 3 types: uniform, random, clumped. Influenced by two factors: distribution of resources and interactions among members of a population.
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What causes clumped distribution?
populations gather around resources, populations that exist in packs. Based off positive interactions.
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What causes uniform distribution?
resources are evenly distributed but scarce. species defend food and shelter ( negative interactions)
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What causes random distribution?
neutral interactions, evenly distributed resources, rarely occurs in nature.
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How would one describe distribution patterns?
fluid, constantly changing
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What is life history?
Understanding survivorship and reproductive patters of individuals to predict population size.
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What is fecunduity?
average number of offspring produced by a female over her lifetime.
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What is survivorship?
The percent of organisms that live to a given age. A cohort is when ecologists follow a group of species born at a similar time to study this.
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Three types of survivorship, what are they?
- Type 1 - live to be mature, few offspring
- Type 2 - risk of mortality is constant throughout lifetime
- Type 3 - die young, many offspring
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What are the four factors that affect population size?
immigration (movement into), emmigration (movement out), birth and death
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A change in population can be determined by what formula?
N/T = B-D
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A Change in population for humans might be determined by what formula?
N = (B+I) - (D + E)
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What formula is used to measure per capita growth rate?
Cgr = (Birth - death)/ Total people
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What is biotic potential?
Highest possible per capita growth rate for a population (ideal conditions), related to fecunduity
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What is exponential growth?
The growth pattern exhibited by a population growing at its biotic portential (J shaped). Occurs in unlimited environments
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What is logistic growth?
exhibited by environments with limited carrying capacity. Lag phase- few organisms to produce followed by rapid growth. Resources become limited, equals out when carrying capacity is reached. S shaped.
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What are r-selected species?
Live close to biotic potential, short life span, sexually mature at a young age, large broods of offspring, little parental care.
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What are k-selected species?
Live close to carrying capacity, long life span, sexually mature later in life, few offspring, lots of parental care.
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What is a density independent factor?
an abiotic factor that affects population growth regardless of population density.
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What is a density dependent factor?
biotic factors that depend on density, like competition or predation. Larger populations will be more greatly affected by biotic factors. (As pop increases, more competition for resources)
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What is intraspecific vs interspecific competition?
- Intra- competition amongst members of the same population
- Inter- competition amongst members of different pops for the same resource
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What are population cycles?
limited prey means limited predators. The alternating periods of large and small population sizes results in sinusodial growth
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What is parasitism?
parasite benefits, host is harmed. Similar to predator prey cycles
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What is mutualism?
both species benefit from the relationship. Growth in one population spurs growth in the other and vv.
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What is commensalism?
- One partner benefits, one is unaffected. growth of host = growth of symbiont
- growth of symbiont does not affect growth of host.
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