© cengage learning 2015 vultures evolved an extreme gut to cope with disgusting dietary habits...

© Cengage Learning 2015

Vultures evolved an extreme gut to cope with disgusting dietary habits November 25, 2014

How is it that vultures can live on a diet of carrion that would at least lead to severe food-poisoning, and more likely kill most other animals? When vultures eat lunch they happily strip the rotting carcasses they find back to the bone. And if, however, the animal's hide is too tough to easily pierce with their beak, they don't hesitate to enter it using other routes, among them the back entrance -- so to speak: via the anus. Although their diet of meat that is both rotting and liberally contaminated with feces would likely kill most other animals, they are apparently immune to the cocktail of deadly microbes within their dinner such as Clostridia, Fuso- and Anthrax-bacteria."To investigate vultures' ability to survive eating this putrid cocktail, we generated DNA profiles from the community of bacteria living on the face and gut of 50 vultures from the USA. Our findings enable us to reconstruct both the similarities, and differences, between the bacteria found in turkey vultures and black vultures, distributed widely in the Western Hemisphere. Apparently something radical happens to the bacteria ingested during passage through their digestive system," says Lars Hestbjerg Hansen, a professor at Aarhus University who together with PhD-student Michael Roggenbuck lead the study while he was at the University of Copenhagen.On average, the facial skin of vultures contained DNA from 528 different types of micro-organisms, whereas DNA from only 76 types of micro-organisms were found in the gut. Michael Roggenbuck explains:"Our results show there has been strong adaptation in vultures when it comes to dealing with the toxic bacteria they digest. On one hand vultures have developed an extremely tough digestive system, which simply acts to destroy the majority of the dangerous bacteria they ingest. On the other hand, vultures also appear to have developed a tolerance towards some of the deadly bacteria -- species that would kill other animals actively seem to flourish in the vulture lower intestine."


BiologyConcepts and Applications | 9eStarr | Evers | Starr


Chapter 40Chapter 40

Population EcologyPopulation Ecology


The biosphere is the global ecosystem, the sum of all the planet’s ecosystems or all of life and where it lives.


40.1 How Do We Describe Populations?

• Ecological factors affect the size, density, distribution, and age structure of a population

• Studying population ecology often involves the use of demographics, which often change over time

• Demographics – Statistics that describe a population


How Do We Describe Populations?

• Biologists frequently use sampling techniques to estimate population size– Plot sampling estimates the total number of

individuals in an area based on direct counts in a small portion of that area

– Estimates from plot sampling are most accurate when the organisms counted are not very mobile and conditions across the area they occupy are more or less uniform



• Population density – Number of individuals per unit area or volume

– Example: Number of dandelions per square meter of lawn

• Population distribution – Describes how individuals are distributed

– Individuals may be clumped, uniformly dispersed, or randomly dispersed in an area



• Scientists use mark-recapture sampling to estimate the population size of mobile animals, such as Florida Key deer

• Mark-recapture sampling – Method of estimating population size of

mobile animals by marking individuals, releasing them, then checking the proportion of marks among individuals recaptured at a later time


40.2 Why Does the Size of a Population Change?

• Immigration – Movement of individuals into a population

– Population increases

• Emigration – Movement of individuals out of a population

– Population decreases

• Zero population growth– Interval in which births equal deaths


Why Does the Size of a Population Change?

• Biotic potential– Maximum possible population growth rate

under optimal conditions

– Under ideal conditions (shelter, food, and other essential resources are unlimited, no predators or pathogens) a population’s growth rate reaches its biotic potential

– Microbes have high biotic potentials

– Large-bodied mammals have low biotic potentials


Why Does the Size of a Population Change?

Exponential Growth Curve


40.3 What Constrains Population Growth?

• Limiting factors– A necessary resource, the depletion of which

halts population growth

– Populations seldom reach their biotic potential because of the effects of limiting factors

– Not always easy to identify all the factors that can restrict population growth


What Constrains Population Growth?

• Limiting factors – Examples: essential resources such as food,

mineral ions, refuge from predators, and safe nesting sites

– In any environment, one essential factor will run out first, and acts as the brake on population growth

– Supplying the first limiting factors simply substitutes one for another – all natural populations eventually encounter limits



• Logistic growth– A pattern of logistic growth shows how a small

population starts growing slowly in size, then grows rapidly, then levels off as the carrying capacity is reached

– Plots out as an S-shaped curve



• Carrying capacity– Maximum number of individuals of a species

that an environment can sustain

– Ultimately, the sustainable supply of resources determines population size


What Constrains Population Growth? P

op

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ize

(nu

mb

er o

f in

div

idu

als)

initial carrying capacity

new carrying capacity

3

4

1

2



• 1944: 29 reindeer introduced to St. Matthew Island

• 1957: 1,350 well-fed reindeer (lichens)

• 1963: 6,000 hungry reindeer (carry capacity exceeded)

• 1966: 42 live reindeer, and many bleached bones

• 1980s: No reindeer


40.4 How Do Life History Patterns Vary?

• Reproduction-related events that occur between birth and death make up a life history pattern

• Life history pattern – A set of traits related to growth, survival, and

reproduction such as life span, age-specific mortality, age at first reproduction, and number of breeding events


How Do Life History Patterns Vary?



• Type I survivorship curve– Elephants have type I survivorship, with low

mortality until old age

– Typical of large animals that bear one or few offspring at a time and provide extended parental care



• Type II survivorship curve

– Snowy egrets are type II population, with a fairly constant death rate

– Typical of lizards, small mammals, and large birds



• Type III survivorship curve

– Sea urchins are type III; mortality is high for larvae and in old age, but low in adults

– Typical of species that produce many small offspring and provide little or no parental care


Percentage of maximum life span

0 50 100

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1

10

100P

erce

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of

surv

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rs (

log

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le)

III

II

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Figure 19.4



• R-selection – Individuals who produce maximum number

offspring as quickly as possible have a selective advantage

– Occurs when population density is low and resources are abundant



• K-selection– Individuals who produce offspring that

outcompete others for limited resources have a selective advantage

– Occurs when a population is near carrying capacity


Time (months)

Po

pu

lati

on

siz

e (N

)

0 1 2 3 4 5 6 7 8 9 10 11 12

0

50

100

150

200

250

300

350

400

450

500

Figure 19.5

Exponential growth of a rabbit population

Ideal conditions

20 rabbits to 475 rabbits in 12 months


Biology and Society:Multiplying Like Rabbits

– In 1859, 12 pairs of European rabbits were released on a ranch in southern Australia.

– By 1865, 20,000 rabbits were killed on just that one ranch.

– By 1900, several hundred million rabbits were distributed over most of the continent.

© 2010 Pearson Education, Inc.


– The European rabbits• Destroyed farming and grazing land

• Promoted soil erosion

• Made grazing treacherous for cattle and sheep

• Competed directly with native marsupials

– The European red fox• Was introduced to control the rabbits

• Spread across Australia

• Ate several species of native birds and small mammals to extinction

• Had little impact on the rabbit population


– In 1950, the Australian government introduced a virus lethal to European rabbits into the rabbits’ Australian environment.

–Did this work?


How Does Predation Affect Life History Traits?

• Overfishing of cod– In response to fishing pressure on larger fish,

Atlantic codfish began maturing faster and reproducing younger

– A 1992 ban on cod fishing came too late to stop the Atlantic cod population from crashing

– Life history changes were early signs of overfishing – had biologists recognized the signs, they might have been able to save the fishery and more than 35,000 jobs


40.6 How Has the Size of the Human Population Changed Over Time?

• For most of history, the human population grew very slowly – In 2009, human population size surpassed 6.8

billion

• Growth rate began to increase about 10,000 years ago, then soared during the past two centuries

• Three trends promoted the large increases


How Has the Size of the Human Population Changed Over Time?

• Three factors of human population growth– Humans were able to migrate into new

habitats and expand into new climate zones

– Humans developed new technologies that increased the carrying capacity of existing habitats

– Humans sidestepped some limiting factors that restrain growth of other species


In the developing world– Death rates have dropped / High birth rates persist

1 Billion : 10,000 Years2 Billion : 123 Years3 Billion : 33 Years4 Billion : 14 Years5 Billion : 13 Years6 Billion : 12 Years7 Billion : 13 Years8 Billion 12 Years9 Billion : 24 Years



• Human skills that override normal population limits– Learned to start fires, build shelters, make

clothing, manufacture tools, and hunts together

– Language allowed knowledge to pass through generations

– Agriculture provided a more dependable food supply



• Human skills that override normal population limits – Improved sanitation and medical advances

(vaccines, antibiotics) cut the death toll from disease

– Energy of fossil fuels allowed development of mechanized agriculture to sustain the ever larger population



• Quality of life is inversely related to population growth, resource depletion, and pollution

• Many governments now offer family planning programs to reduce fertility rates

• Worldwide, total fertility rate has fallen from 6.5 in 1950 to 2.6 in 2008; and replacement fertility rate for developed countries is 2.1



• Age structure diagrams show the age distribution of individuals – The broader the base of an age structure

diagram, the greater proportion of young people, and the greater expected growth

– More than 1/3 of the world population is in the broad pre-reproductive base

– World population growth can’t be slowed for many years, because 1.9 billion people are about to enter reproductive age



• Future growth– World population is expected to reach 8.9

billion by 2050, and possibly to decline as the century ends

– China and India each hold more than one billion people (together, 38% percent of the world population); the United States is third, with 307 million


40.7 How Does Industrialization Affect Population Growth?

• The most highly developed countries have the lowest birth rates and infant mortality, and the highest life expectancy

• High population growth is correlated with low levels of economic development, and low per capita consumption of resources

• Negative population growth in some countries also poses challenges


How Does Industrialization Affect Population Growth?

• On a per capita basis, people in highly developed countries use far more resources than those in less developed countries, and generate more waste and pollution


How Does Industrialization Affect Population Growth?

• Ecological footprint – Area of Earth’s surface required to sustainably

support a particular level of development and consumption

– People in China and India consume less than average

– Per capita footprint of the United States is more than three times average


How Does Industrialization Affect Population Growth? (cont’d.)


11/26 Friday SchedulePopulations

40 11/28 No Class

12/3 Ecology Succession

41 12/5 Trophic Levels 42

12/10 Biomes & Human Effect

43&44 12/12 Lecture ReviewLab Final Exam

12/17 Final Exam 12/19 Make up class if needed

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