Title: Ecology and evolution: Populations, communities, and biodiversity
14
- Ecology and evolution Populations, communities,
and biodiversity
2This lecture will help you understand
- How evolution generates biodiversity
- Speciation, extinction, and the biodiversity
crisis - Population ecology
- Community ecology
- Species interactions
- Conservation challenges
- Evolution by natural selection
3Key Words
adaptation adaptive trait age distribution age
structure age structure diagrams allopatric
speciation anthropogenic artificial
selection biodiversity biological
diversity biosphere biotic potential carnivores ca
rrying capacity climax community clumped
distribution community competition decomposers
host immigration interspecific competition intrasp
ecific competition invasive species keystone
species K-strategist limiting factors logistic
growth mass extinction mutations mutualism natural
selection niche omnivores parasite parasitism
density dependent detritivores ectoparasites Emigr
ation endemic endoparasites environmental
resistance evolution exponential
growth extinction food chain food
web fossil fossil record growth rate habitat
selection habitats herbivores heritable
4Key Words
sex ratio speciation species succession symbioses
tertiary consumers trophic levels uniform
distribution
phylogenetic trees pioneer species pollination pop
ulation density population dispersion population
distribution population growth curves population
size predation predator prey primary
consumers primary succession random
distribution resource partitioning r-strategists s
econdary consumers secondary succession
5Central Case Striking Gold in a Costa Rican
Cloud Forest
- The golden toad of Monteverde, discovered in
1964, had disappeared 25 years later. - Researchers determined that warming and drying of
the forest was most likely responsible for its
extinction. - As the global climate changes, more such events
can be expected.
6Biodiversity
- Biodiversity, or biological diversity, is the sum
of an areas organisms, considering the diversity
of species, their genes, their populations, and
their communities. - A species is a particular type of organism a
population or group of populations whose members
share certain characteristics and can freely
breed with one another and produce fertile
offspring.
7Biodiversity
- Costa Ricas Monteverde cloud forest is home to
many species and possesses great biodiversity.
Figure 5.1
8Natural selection
- Natural selection rests on three indisputable
facts - Organisms produce more offspring than can
survive. - Individuals vary in their characteristics.
- Many characteristics are inherited by
offspring from parents.
9Natural selection
- THEREFORE, logically
- Some individuals will be better suited to
their environment they will survive and
reproduce more successfully. - These individuals will transmit more genes to
future generations. - Future generations will thus contain more
genes from better-suited individuals. - Thus, characteristics will evolve over time to
resemble those of the better-suited ancestors.
10Natural selection
- Fitness the likelihood that an individual will
reproduce - and/or
- the number of offspring an individual
produces over its lifetime - Adaptive trait,
- or adaptation a trait that increases an
individuals fitness
11Natural selection
- Evidence of natural selection is all around us
- In nature
- Diverse bills have evolved among species of
Hawaiian honeycreepers.
Figure 4.23a
12Beak Types Resulting From Natural Selection
13Natural selection
- Evidence of natural selection is all around us
- and in our domesticated organisms.
Dog breeds, types of cattle, improved crop
plantsall result from artificial selection
(natural selection conducted by human breeders).
Figure 4.23b
14Speciation
- The process by which new species come into being
- Speciation is an evolutionary process that has
given Earth its current species richnessmore
than 1.5 million described species and likely
many million more not yet described by science. - Allopatric speciation is considered the dominant
mode of speciation, and sympatric speciation also
occurs.
15Allopatric speciation
- 1. Single interbreeding population
- 2. Population divided by a barrier
subpopulations isolated
Figure 5.2
16Allopatric speciation
- 3. The two populations evolve independently,
diverge in their traits. - 4. Populations reunited when barrier removed, but
are now different enough that they dont
interbreed.
Figure 5.2
17Allopatric speciation
- Many geological and climatic events can serve as
barriers separating populations and causing
speciation. - on.
18(No Transcript)
19Stanley Miller's experiment animation.
Click to view animation.
20Stabilizing Selection
Click to view animation.
21Disruptive Selection
Click to view animation.
22Niches and Natural Selection
23Various Niches and Their Adaptations
24Geographic Separation
25Mimicry
26Phylogenetic trees
- Lifes diversification results from countless
speciation events over vast spans of time. - Evolutionary history of divergence is shown with
diagrams called phylogenetic trees. - Similar to family genealogies, these show
relationships among organisms.
27Phylogenetic trees
- These trees are constructed by analyzing patterns
of similarity among present-day organisms. - This tree shows all of lifes major groups.
Figure 5.4
28Phylogenetic trees
- Within the group Animals in the previous slide,
one can infer a tree of the major animal groups.
Figure 5.4
29Phylogenetic trees
- And within the group Vertebrates in the previous
slide, one can infer relationships of the major
vertebrate groups, and so on
Figure 5.4
30Extinction
- Extinction is the disappearance of an entire
species from the face of the Earth. - Average time for a species on Earth is 110
million years.Species currently on Earth the
number formed by speciation minus the number
removed by extinction.
31Extinction
- Some species are more vulnerable to extinction
than others - Species in small populations
- Species adapted to a narrowly specialized
resource or way of life -
- Monteverdes golden toad was apparently such a
specialist, and lived in small numbers in a small
area.
32Extinction
- Some species are more vulnerable to extinction
than others - Species in small populations
- Species adapted to a narrowly specialized
resource or way of life -
- Monteverdes golden toad was apparently such a
specialist, and lived in small numbers in a small
area.
33Lifes hierarchy of levels
- Life occurs in levels
- from the atom up to
- the molecule to
- the cell to
- the tissues to
- the organs to
- the organism
Figure 5.7
34Lifes hierarchy of levels
- and from the organism to the population to
- the community to
- the ecosystem to
- the biosphere.
- Ecology deals with these levels, from the
organism up to the biosphere.
Figure 5.7
35Ecology
- The study of
- the distribution and abundance of organisms,
- the interactions among them,
- and the interactions between organisms and
their abiotic environments - Ecology is NOT environmental advocacy!
- ( a common MISUSE of the term)
36Habitat and niche
- Habitat the specific environment where an
organism lives (including living and nonliving
elements rocks, soil, plants, etc.) - Habitat selection the process by which
organisms choose habitats among the options
encountered - Niche an organisms functional role in a
community (feeding, flow of energy and matter,
interactions with other organisms, etc.)
37Population ecology
- Population a group of individuals of a species
that live in a particular area - Several attributes help predict population
dynamics (changes in population) - Population size
- Population density
- Population distribution
- Age structure
- Sex ratio
38Population size
- Number of individuals present at a given
timePopulation size for the golden toad was
1,500 in 1987, and zero a few years later.
39Population density
- Number of individuals per unit area or,
- Number of individuals per unit volume
- Population density for the harlequin frog
increased locally as streams dried and frogs
clustered in splash zones.
40Population distribution
- Spatial arrangement of individuals
Clumped
Random
Uniform
Figure 5.8
41Age structure
- Or age distribution relative numbers of
individuals of each age or age class in a
population - Age structure diagrams, or age pyramids, show
this information.
Figure 5.9
42Age structure
Pyramid weighted toward young population growing
Pyramid weighted toward old population declining
Figure 5.9
43Sex ratio
- Ratio of males to females in a population
- Even ratios (near 50/50) are most common.
- Fewer females causes slower population growth.
- Note human sex ratio biased toward females at
oldest ages.
44Population growth
- Populations grow, shrink, or remain stable,
depending on rates of birth, death,
immigration, and emigration. - (birth rate immigration rate)
- (death rate emigration rate)
- population growth rate
45Exponential growth
- Unregulated populations increase by exponential
growth - Growth by a fixed percentage, rather than a
fixed amount. - Similar to growth of money in a savings account
46Exponential growth in a growth curve
- Population growth curves show change in
population size over time. - Scots pine shows exponential growth
Figure 5.10
47Limits on growth
- Limiting factors restrain exponential population
growth, slowing the growth rate down. - Population growth levels off at a carrying
capacitythe maximum population size of a given
species an environment can sustain. - Initial exponential growth, slowing, and
stabilizing at carrying capacity is shown by a
logistic growth curve.
48Logistic growth curve
Figure 5.11
49Population growth Logistic growth
- Logistic growth (shown here in yeast from the
lab) is only one type of growth curve, however.
Figure 5.12a
50Population growth Oscillations
- Some populations fluctuate continually above and
below carrying capacity, as with this mite.
Figure 5.12b
51Population growth Dampening oscillations
- In some populations, oscillations dampen, as
population size settles toward carrying capacity,
as with this beetle.
Figure 5.12c
52Population growth Crashes
- Some populations that rise too fast and deplete
resources may then crash, as with reindeer on St.
Paul Island.
Figure 5.12d
53Density dependence
- Often, survival or reproduction lessens as
populations become more dense. - Density-dependent factors (disease, predation,
etc.) account for the logistic growth curve.
54Biotic potential and reproductive strategies
- Species differ in strategies for producing
young. - Species producing lots of young (insects, fish,
frogs, plants) have high biotic potential. - Others, such as mammals and birds, produce few
young. - However, those with few young give them more
care, resulting in better survival.
55Biotic Potential
56Survivorship
57K-strategists
Terms come from K symbol for carrying
capacity. (Populations tend to stabilize near K.)
58r-Selected
- r intrinsic rate of population increase.
(Populations can potentially grow fast, have high
r.)
59Community ecology
- Ecologists interested in how populations or
species interact with one another study community
ecology. - Community a group of populations of different
species that live in the same place at the same
time - e.g., Monteverde cloud forest
communitygolden toads, quetzals, trees,
ferns, soil microbes, etc.
60Roles in communities Producers
- By eating different foods, organisms are at
different trophic levels, and play different
roles, in the community - Plants and other photosynthetic organisms are
producers.
Figure 5.14b
61Primary consumers
- Animals that eat plants are primary consumers, or
herbivores, and are at the second trophic level.
Figure 5.14b
62Secondary consumers
- Animals that eat herbivores are secondary
consumers, at the third trophic level.
Figure 5.14b
63Detritivores and decomposers
- Detritivores and decomposers eat nonliving
organic matter they recycle nutrients.
Figure 5.14b
64Trophic levels
- Together these comprise trophic levels.
Figure 5.14b
65Food chains and webs
- We can represent feeding interactions (and thus
energy transfer) in a community - Food chain Simplified linear diagram of who eats
whom - Food web Complex network of who eats whom
66Food web for an eastern deciduous forest
Figure 5.14a
67Keystone species
- Species that have especially great impacts on
other community members and on the communitys
identity - If keystone species are removed, communities
change greatly.
A keystone holds an arch together.
Figure 5.15a
68Keystone species
- When the keystone sea otter is removed, sea
urchins overgraze kelp and destroy the kelp
forest community.
Figure 5.15b
69Balance of Life
70Predation
- One species, the predator, hunts, kills, and
consumes the other, its prey.
Figure 5.16
71Predation drives adaptations in prey
Cryptic coloration Camouflage to hide from
predators
Warning coloration Bright colors warn that prey
is toxic
Mimicry Fool predators (here, caterpillar mimics
snake)
Figure 5.18
72Competition
- When multiple species seek the same limited
resource - Interspecific competition is between two or
more species. - Intraspecific competition is within a
species. - Usually does not involve active fighting, but
subtle contests to procure resources.
73Interspecific competition
- Different outcomes
- Competitive exclusion one species excludes the
other from a resource. - Species coexistence both species coexist at a
ratio of population sizes, or stable equilibrium.
74Competitive Exclusion Principle
Click to view animation.
75Interspecific competition
- Adjusting resource use, habitat use, or way of
life over evolutionary time leads to - Resource partitioning species specialize in
different ways of exploiting a resource. - Character displacement physical characters
evolve to become different to better
differentiate resource use.
76Resource partitioning
- Tree-climbing bird species exploit insect
resources in different ways.
Figure 5.20
77Parasitism
- One species, the parasite, exploits the other
species, the host, gaining benefits and doing
harm.
Figure 5.21
78Mutualism
- Both species benefit one another.
- Hummingbird pollinates flower while gaining
nectar for itself.
Figure 5.22
79Mutualism
80Succession
- A series of regular, predictable, quantifiable
changes through which communities go - Primary succession Pioneer species colonize a
newly exposed area (lava flows, glacial retreat,
dried lake bed). - Secondary succession The community changes
following a disturbance (fire, hurricane,
logging).
81Primary aquatic succession
- 1. Open pond
- 2. Plants begin to cover surface sediment
deposited - 3. Pond filled by sediment vegetation grows over
site
Figure 5.24
82Secondary terrestrial succession
Figure 5.23
83Succession
Click to view animation.
84Ecosystem Characteristics at Immature and Mature
Stages of Ecological Succession
Characteristic Ecosystem Structure Plant
size Species diversity Trophic
structure Ecological niches Community
organization (number of interconnecting
links) Ecosystem Function Biomass Net primary
productivity Food chains and webs Efficiency of
nutrient recycling Efficiency of energy use
Immature Ecosystem (Early Successional
Stage) Small Low Mostly producers, few
decomposers Few, mostly generalized Low Lo
w High Simple, mostly plant
herbivore with few decomposers Low Low
Immature Ecosystem (Late Successional
Stage) Large High Mixture of producers,
consumers, and decomposers Many, mostly
specialized High High Low Complex,
dominated by decomposers High High
Table 8-1Page 158
85Invasive species
- A species that spreads widely and rapidly becomes
dominant in a community, changing the communitys
normal functioning - Many invasive species are non-native, introduced
from other areas. - Purple loosestrife invades a wetland.
Figure 5.25
86Climate change and Monteverde
- Monteverdes cloud forest become drier in the
1970s1990s.
Stream flow fell
Number of dry days rose
From The Science behind the Stories
87Climate change and Monteverde
- Cool ocean low clouds mountains receive
moisture - Warm ocean high clouds mountains get less
moisture
From The Science behind the Stories
88Viewpoints Conservation of Monteverde?
Robert Lawton
Nathaniel Wheelwright
A few committed people can have an impact.
Conservation efforts must take into account local
social aspirations. Conservation can lead to
economic success. But local conservation is not
enough.
Whatever negative local impact the steady
onslaught of ecotourists may have on resplendent
quetzals and howler monkeys, it is more than
compensated for by inspiring people to appreciate
tropical forests and their own natural heritage.
From Viewpoints
89Conclusions Challenges
- Earths biodiversity faces a mass extinction
event caused by human actions. - Climate change may alter communities and cause
species extinctions. - Invasive species pose a new threat to community
stability. - Conservation efforts need to consider local
economies and social conditions in order to
succeed. - Evolution and natural selection provide a strong
explanation for how Earths life diversified.
90Conclusions Solutions
- There is still time to avoid most species
extinctions threatened by human actions. - Studies like those at Monteverde are clarifying
the effects of climate change. - Ecological restoration efforts can remove
invasive species and restore original
communities. - Many conservation efforts today are locally run
or promote local economies.
91QUESTION Review
- Allopatric speciation requires?
- a. Natural selection
- b. More than two populations
- c. Some kind of barrier separating populations
- d. Sex ratio bias in one population
92QUESTION Review
- Which is a K-strategist?
- a. A dragonfly that lays 300 eggs and flies away
- b. An oak tree that drops its acorns each year
- c. A bamboo plant that flowers only once every 20
years - d. A human who raises three children
- e. A fish on the second trophic level
93QUESTION Review
- Which of the following lists of trophic levels is
in the correct order? - a. Producer, secondary consumer, herbivore
- b. Producer, herbivore, secondary consumer
- c. Secondary consumer, producer, detritivore
- d. Herbivore, carnivore, producer
94QUESTION Review
- Primary succession would take place on all of the
following EXCEPT? - a. The slopes of a Hawaiian volcanos new lava
flow - b. A South Carolina coastal forest after a
hurricane - c. Alaskan land just uncovered as a glacier melts
- d. A new island formed by falling levels of a
reservoir in Ohio
95QUESTION Weighing the Issues
- Can we continue raising the Earths carrying
capacity for humans by developing technology and
using resources more efficiently? - a. Yes, our growth can continue indefinitely.
- b. Our growth can continue some more, but will
eventually be halted by limiting factors. - c. No, we cannot raise Earths carrying capacity
for ourselves any longer.
96QUESTION Weighing the Issues
- Are national parks and preserves the best way to
conserve biodiversity? - a. Yes, because species depend on their habitats
and intact communities being protected. - b. No, because climate change can ruin
conservation efforts if it changes conditions
inside preserves. - c. Ecotourism and encouraging local interest in
conservation is more important than establishing
parks.
97QUESTION Interpreting Graphs and Data
- You would expect this population to be?
- a. Growing rapidly
- b. Shrinking rapidly
- c. Stable in size
- d. Oscillating in size
Figure 5.9
98QUESTION Interpreting Graphs and Data
- How can you tell that this population growth
curve shows exponential growth? - a. Population is increasing.
- b. Data points match curve closely.
- c. Population is rising by the same number
during each interval. - d. Population is rising by the same percentage
during each interval.
Figure 5.10
99QUESTION Interpreting Graphs and Data
- This shows growth ending at a(n)
. - a. exponential carrying capacity
- b. intrinsic equilibrium
- c. logistic carrying capacity
- d. runaway equilibrium
- e. logistic extinction
Figure 5.12a
100QUESTION Viewpoints
- What is the most important lesson we can learn
from the Monteverde preserve? - a. Preserves do little good if species can become
extinct inside them. - b. Climate change means that we will need more
than preserves to save all species. - c. Ecotourism and local participation can make
for successful conservation.