Quantitative Ecology Chap 12

8/13/2019 Quantitative Ecology Chap 12

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CHAPTER 12

Quantitative ecology


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Quantitative ecology

Outline

Population ecology

Population dispersion

Biotic potential

Factors influencing population growth

Life history patterns


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Population ecology

population consists of the individuals of a species that

occur together at one place at one time

three important aspects of population

i. the range throughout which a population occurs

ii. dispersion of individuals within that range

iii. size of the population attains

Population distributions

most species have relatively limited geographic range


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Randomly spaced

not common in nature

individuals do not interact strongly one another

Uniformly spaced

always results from competition for resources

in animals, it occurs because individuals tend to

defend their territories which provide them resources

among plants, results of competition for the sunlight,

nutrients or water


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Biotic potential

to understand populations, we must consider how they

grow and factors in nature limit population growth

The exponential growth model

the actual rate of population increase

r= (b-d) + (i-e) r= difference between the birthrate (b) and death rate (d)e= movement out of area and i= movement into area

movement of individuals have a major impact onpopulation growth rates


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Biotic potential

biotic potential = rate at which a population of a given

species will increases when no

limits are placed on its rate of

growthdN/dt = riN, N = num. of individuals in population,

dN/dt = rate of change in its num. over time

ri = innate capacity for growth

innate capacity of growth of any population isexponential


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Biotic potential

Carrying capacity

how rapidly population grows, they will reach limit

imposed by several factors such as space, light, water..

carrying capacity,K = maximum number ofindividuals that environment can support


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Biotic potential

Logistic growth model

as population reaches its carrying capacity, its rate of

growth slows greatly because lack of resources

dN/dt = rN(K-N/K)

as N increases, the fraction by r is multiplied becomes

smaller, and the rate population increases decline

in many cases, real population display trendscorresponding to a logistic growth curve


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Models of population growth


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Population growth is limited by the

environment

population dynamics - study of factors that affectgrowth, stability and decline of population known

population undergo three distinct phase

i. growthii. stability

iii. decline

population growth occurs when resources exceed thenumber of individuals able to use them

reproduction is rapid and death rates are low, increasein population size


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Population growth is limited by the

environment

population stability is always the longest phase,

growing population outstrips its available resources,

decline occurs because decrease in the individuals

number in a population, lead to extinctionFactors influencing population growth

as long resources available, almost all populations will

ten to grow exponential affect by birth rate and death rate

intrinsic rate = birth rate death rate


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The influence of population density

density-dependent = population size affect populationgrowth rate

when population approach their carrying capacity,

competition can be severe, increased risk of mortalityand decrease birthrate

predators tend to focus on particularly common prey,increased rates of mortality as population increase

high population led to accumulation of toxic wastes

behavioral changes also affect population growth rates,results from hormonal actions


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crowded populations may led to decreased in

population growth rate because of emigration factor

in some cases, growth rate increase with increase

population size (Allee effect) individuals are difficult finding mates in population

that are too sparsely distributed, some species rely on

large groups to deter predator


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Density-independent effects

rate of growth of a population at any instant is limited

by something other that the size of population

factors such as extremely cold winter, drought, storms,volcanic eruptions may affects populations

when such events occurs, population extremely

decrease and will increase rapidly when environmentback to normal


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Survivorship curves

survivorship is defined as the percentage of an originalpopulation that survives to a given age

Type I

- flat at early and middle life and drops suddenlyas death rate increases among the elderly

- associated with species such as humans and otherlarge mammals that produce few offspring that

are well cared for.Type II

- intermediate, mortality more constant over lifespans, can be seen in Hydra and the grey

squirrels


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Type III

- very high death rates for the young, followed bylower death rates

- often associated with organisms, such as oysters,that produce very many offspring but

provide little or no care.

some invertebrates show a "stair-stepped" curve withbrief periods of high mortality during molts, followed

by periods of lower mortality when the exoskeleton ishard.


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Survivorship curves

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the logistic population model predicts two main lifehistory patterns.

most populations cannot be characterized as either r-orK-strategists; they have intermediate characteristics.

r-Selectiona. species that undergo selection to maximize their

rate of natural increase

b. often opportunistic species, tend to be colonizers.

c. strategy for continued existence is based onindividuals having the following traits: (small size,short life span, mature fast, produce manyoffspring, engage in little caring of offspring)


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d. such populations usually exhibit a survivorshipcurve similar to type III.

e. thus, they rely on rapid dispersal to newunoccupied environments.

K-Selectiona. species that hold their populations fairly constant

near the carrying capacity

b. such populations are equilibrium species, tend to

be specialists rather than colonizers, and maybecome extinct when their evolved way of life isdisrupted (grizzly bear, Florida panther, etc.).


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c. overall strategy for continued existence is based onhaving the following traits: (large size, long lifespan, slow to mature, produce few offspring,expend considerable energy in care)

d. such populations usually have a survivorshipcurve similar to type I.

e. thus, they rely on competitive superiority tosecure limited resources.


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Population pyramids

at the beginning of twentieth century, humanpopulation grow rapidly

different countries shows different growth rate (eg.Mexico grow rapidly)

rate which population can be expected to grow in thefuture can be represent by population pyramids

human population pyramid displays the age population

by sex, female in most region have longer lifeexpectancy than male


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Population pyramids

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Quantitative Ecology Chap 12

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