es 10ecologyf11ncrane/es 10/es 10ecologyf11.pdf · species tolerance • law of tolerance: the...

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Ecology and ecosystems: the here and now

We’ll explore the processes that drive living systems

A word about habitat fragmentation

It limits response options for populations in the face of change. It disrupts migratory patterns…

Fences create a unique type of fragmentation

•  Feedback loops* •  Trophics and energetics (food webs)*

– Trophic forcing •  Adaptation/Natural selection •  Speciation •  Tolerance limits •  Abiotic and biotic factors •  Species interactions

Human Impact on Ecosystems�

The response of systems�

Positive feedback - eutrophication�

Negative feedback – population and food availability

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Dead zones in the oceans - eutrophication •  Eutrophication •  Too many nutrients lead to

phytoplankton blooms •  Phytoplankton blooms lead to

zooplankton blooms, fish etc…

•  Organisms die, this leads to high bacterial populations (decomposers) which deplete oxygen

•  This leads to more death •  Stratification and oxygen

depletion on the bottom •  Can affect all trophic levels,

but it takes time

The large region of low oxygen water often referred to as the 'Gulf Dead Zone,' shown here, crosses nearly 5,800 square miles of the Gulf of Mexico again in what

appears to be an annual event

Polar bears: Ursus maritimus

•  Adaptation in the face of rapid change

•  Federally listed endangered

What’s the problem with rapid climate change for living organisms?

•  They cannot always adapt fast enough •  They may survive but be relegated to

‘refugia’ •  Many will suffer genetic bottlenecks as a

result •  Biomes will shift and organisms will have

to shift with them (or not)

Refugia and habitat fragmentation

Some organisms CAN survive in these refugia, but may never get out, or may emerge quite changed

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Attempting to maintain healthy populations is also about ecological stability, especially for top predators. This of course is about human stability too.

Some systems are open, some are closed, most are permeable…

(leaky)

•  Nutrients tend to be cycled tightly (closed) in forest systems

•  Energy can be very ‘leaky’

Primary productivity Primary production: Plant accumulation of energy from the sun.

Productivity: rate of that production. Autotrophs or producers

3-11

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Trophic levels Figure 2.14

2-12


Energy pyramid Figure 2.15

2-13 Source: Data from Howard T. Odum, “Trophic Structure and Productivity of Silver Springs, Florida” in Ecological Monographs, 27:55-112, 1957, Ecological Society of America.

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Top predators can have large effects on ecosystem structure due in part to their high energy needs. This can lead to top down forcing or trophic cascades

Producers can also have large effects on ecosystem structure due to their role in supplying the energy in the first place. This can lead to bottom up forcing

Wolves in Yellowstone

Wolves-the unexpected impacts

•  Elk were eating riparian (river) trees and shrubs

•  Birds and steelhead had declined - ecosystem change

•  Wolves drove Elk up into higher ground •  Riparian systems are recovering, ecosystem

is shifting back

Ecosystem change: an example

Reduction of coral = increase in Algae. This shifts functional Groups of species, and affects Primary productivity


Killer whales and their appetite for sea otters

Life on Earth • Living things cause change • Living things respond to change • Living things change their environments • Living (biotic) and non-living (abiotic)

components of our Earth interact • Processes like global warming/climate

change follow large-scale patterns, but the composition of life on earth that can affect those patterns

• Ecological systems exist in balance - that balance can be disturbed, and its evolution from there can be difficult to predict.

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Natural Selection Adaptation� Evolution

•  Co-evolution •  Convergent evolution

Function and design

Charles Darwin Alfred Russel Wallace

Natural Selection The Galapagos mockingbirds differ only slightly in size, shape, and coloration.

Nesomimus macdonaldi Nesomimus melanotis

Nesomimus parvulus Nesomimus trifasciatus

Darwin reasoned that they are similar because they share a common ancestor.

N. mac

dona

ldi

N. mela

notis

N. p

arvu

lus

N. trifa

sciat

us

Geographic proximity of similar but distinct species

Natural selection: Facts and inferences

Fact 1. Natural populations have large excess reproductive capacities.

Fact 2. Population sizes generally remain stable.

Fact 3. Resources are limiting.

Inference 1. A severe struggle for existence must occur.

Fact 4. An abundance of variation exists among individuals of a species.

Fact 5. Some of this variation is heritable.

Inference 2. Genetically superior individuals outsurvive and outreproduce others.

Inference 3. Over many generations, evolutionary change must occur in the population.

Experimental Evidence of Evolution by�Natural Selection

•  Case Study of Natural Selection by Pollinators of Alpine Skypilot Plants

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In tundra habitats above timberline, the alpine skypilot is pollinated primarily by bumblebees.

In forested habitats below timberline, the alpine skypilot is pollinated primarily by flies.

Below-timberline flower: small and skunky-smelling Flower size (mm)

Num

ber o

f ind

ivid

uals

10 12 14 16 18 20 22

10

8

6

4

2

0

Tundra flower: big and sweet-smelling Flower size (mm)

Num

ber o

f ind

ivid

uals

28 24 20 16 12 8 4 0

10 12 14 16 18 20 22

•  Feedback loops* •  Trophics and energetics (food webs)*

– Trophic forcing •  Adaptation/Natural selection •  Speciation •  Tolerance limits •  Abiotic and biotic factors •  Species interactions •  Populations

- overdominance occurs when fitness of the heterozygote exceeds either homozygote.

Alleles: HbA = normal hemoglobin allele HbS = sickle cell allele

Genotypes: Relative fitness HbA HbA: susceptible to malaria

HbA HbS: resistant to malaria, experiences mild anemia

HbS HbS: susceptible to severe anemia

The sickle cell allele 20

15

10

5

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

2

3

5

7

10

20

30

50

70

100

Birthweight (pounds)

Percentage of mortality

Perc

enta

ge o

f Pop

ulat

ion

Heavy mortality on extremes

Mortality

For example, very small and very large babies are most likely to die, leaving a narrower distribution of birthweights.

6 7 11 10 8 9

Beak length (mm)

10

0

20

30

Num

ber o

f ind

ivid

uals

For example, only juvenile blackbellied seedcrackers with very long or very short beaks survived long enough to breed.

• Survival and differential reproductive success over a period of time

• Traits that increase ‘fitness’ are ‘selected for’, and are passed on through generations

Adaptation by the process of Natural Selection

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Adaptation, speciation, and the concept of the niche Niche

The ‘role’ an organism plays in its environment/ecosystem

1 niche = 1 species

Competitive exclusion principle (CEP) = if there are two species, one will outcompete the other and ‘win’, OR, a process of niche partitioning will begin. They will divide up and ‘share’ the parts of the niche


Galápagos finches Figure 3.5

3-2


Warblers in tree Figure 3.8

3-6 Source: Original observation by R. H. MacArthur.

Speciation: new species evolve, others go extinct

Allopatric speciation: speciation occurs as a result of a physical separation - barriers

Sympatric speciation: speciation occurs as a result of hybridization – within a population, a new species arises

Sexual selection is a (one) strong force maintaining separate species

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Taxonomy Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Taxonomy of two common species

3-3

Five Kingdoms Three Domains

Evolutionary Trees Evolution/adaptation can also lead to design ‘innovations’ –

increase fitness The Flower and fruit allowed the angiosperms (flowering plants) to diversify to over 300,000 species

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Pitfalls

-  Giraffes

- Polar Bears

The neck of the Giraffe


Most feeding is done below neck height.

Males Females

1

2

3

4

5

6

7

0

Feed

ing

heig

ht (m

eter

s)

Percentage of feeding bites 0 20 40

1

2

3

4

5

6

7

0 0 20 40


Fighting

Male-male competition “Simmons and Schemers (1996)”

http://www.youtube.com/watch?v=C7HCIGFdBt8

Gerenuks (Giraffe necks)

Polar Bears

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Polar Bears

233 “sit and wait”

1 “sneak and pounce”

54 “jump and crush”

“Sterling 1974” Polar Bears

UV Hypothesis

What you have learned so far:

Ecological systems experience perturbations. The System will ‘react’ depending on the nature of those perturbations (resulting in positive and negative feedbacks), and the type of system (open, closed)

Trophic cascades and top down/bottom up forcing are energetic perturbations. These can even result in ‘phase shifts’ like on some coral reefs.

Habitat fragmentation creates unique challenges for ecosystem response (at the population level)

What you have learned so far:

Natural selection/adaptation and evolution follow the simple rule of fitness

What is fitness and how do behaviors/patterns lead to fitness?

Speciation maintains diversity. Taxonomy describes relationships between species and sheds light on origins

Species Diversity

•  What is species diversity: both – Species richness – Relative abundance

•  What leads to high diversity? – Habitat heterogeneity – High levels of competition – Other…interspecific interactions, functional

group diversity, abiotic factors?

Some important concepts •  What is a niche? -

– The ‘role’ of an organism –  Its use of abiotic and biotic resources, and its

reaction to them (eg. Tolerance plays a role here)

•  Competitive Exclusion Principle – No two species can occupy the same niche - it

will always result in competition

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•  Generalists •  Specialists Effects of competition •  Competitive exclusion: One species dominates •  Resource partitioning – a niche can be

‘partitioned’: owls/hawks •  Competition can lead to speciation •  Competition is an important factor in

maintaining ecosystem function. When one species is removed, the structure of competition is changed too.

•  Introduced species?


Tolerance limits Figure 3.2

3-1

Species tolerance •  Law of tolerance: the existence, abundance and

distribution of a species in an ecosystem are (largely) determined by whether the levels of one or more factors (abiotic) falls within the range of tolerance

•  Tolerance to abiotic and biotic factors in part determines the range/distribution

Factors affecting organisms

•  Abiotic: non-living (temperature, water, sedimentation etc.) physical and chemical

•  Biotic: living interactions (between living organisms) – Symbiosis – Predation – Herbivory – Competition

Abiotic factors are important in determining ecosystem structure

•  Living things have tolerance limits to abiotic factors such as…?

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Species Interactions (Biotic): Interspecific and Intraspecific

•  Competition •  Predation •  Symbiosis

Zooxanthellae: the key to coral reef productivity


Reduction of coral = increase in Algae. This shifts functional Groups of species, and affects Primary productivity

Cleaning symbiosis: mutualism

mutualism

Predation

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Herbivory has large effects on ecosystems Ecosystem structure

•  Keystone species - is there such a thing? – A species whose ‘role’ or niche has a major

impact on the structure of an ecosystem

– Some case studies?


Killer whales and their appetite for sea otters

Predators: Sea Otters

Sea Otters and Sea Urchins:�a kelp forest paradigm

Sea Urchins eat kelp, especially new recruits If kept in check, they eat drift kelp If populations expand, they will eat established kelp

Sea Otters eat urchins, especially exposed ones They will keep sea urchin populations in check

The Aleutian Island studies

Sea Otters as a keystone predator

Reproductive strategies

•  K and r selection •  K - selection: few

offspring with high investment

•  r - selection: produce as many as possible and invest little

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Reproductive strategies

3-10

Population Viability Analysis •  Chances of a population persisting or becoming extinct •  What are the specific characteristics of this population?

•  Takes into account: –  Habitat disturbances –  Genetic variability –  Life History Characteristics –  Fertility –  Birth and Death rates

Minimum viable population Minimum habitat needed Effective population size


J and S population curves Figure 3.20

3-9

Exponential growth is growth with no limiting factors (or few)

Logistic growth is what happens when populations reach carrying capacity, and respond to limits


Population oscillations Figure 3.18

3-7


Predator-prey oscillations Figure 3.19

3-8 Source: Data from D. A. MacLulich, Fluctuations in the Numbers of the Varying Hare (Lepus americus), Toronto: University of Toronto Press, 1937, reprinted 1974.

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Populations: what affects their size and growth?

•  Density (#/area) - carrying capacity (K) •  Natality - birth rate •  Mortality - death rate •  Age distribution/sex ratio •  Spatial distribution •  Resource availability •  Species interactions •  Migration/emmigration

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