ecology and ecosystems: the here topics and noncrane/es 10/documents/es10ecologyf13pdf.pdf ·...

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Ecology and ecosystems: the here and now Topics

•  Systems (again) •  Abiotic and biotic factors affecting

ecosystems •  Tolerance (to these factors) •  A side trip – habitat fragmentation •  Adaptation in the face of rapid change

Feedback loops: ecological, physiological…

•  Positive feedback: positive change in a state variable (eg. Nutrient input) leads to a positive response (higher growth etc.). These can ‘run away’ if not controlled. Eutrophication.

•  Negative feedback: Increase leads to decrease – too many predators=few prey=lower population of predators. These can lead to stability (homeostasis)

What is an ecosystem in balance?

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

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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-seasonal

Stability?

Resilience – return? Phase (state) shifts

Changed state

Ecology is the study of interactions between living things and the living and non-living components of their environment

Organismal/physiological ecology Population ecology Community ecology Behavioral ecology Ecosystems

Factors affecting organisms

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

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

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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 •  Tolerance can be gradual or show a threshold

effect

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

Tolerance limits Figure 3.2

3-1

A word about habitat fragmentation

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

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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Fences create a unique type of fragmentation

Ecosystem stability again •  These forces (feedbacks), including things

like disease, keep populations ‘stable’ which keeps ecosystems ‘stable’.

•  But the planet has always been changing, and the living systems change too – in response to abiotic change and biotic pressures.

•  Adaptation

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)

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

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But some adapt rapidly – especially ‘invasives’ Purple Loosestrife Lythrum salicaria It flowers about three weeks earlier along its northern range (into Canada now) – giving it a 30 fold increase in seed production. Advantage of delayed flowering includes growing larger – favored in the southern range. All this in 50 years!

Montipora sp. Is a coral that is taking over large areas of reef in Pacific Islands. This within the past 40 years. Appears to be outcompeting other corals due to a higher tolerance to acidity (lower PH)

And Simon says…

So what does all that mean? Ecologists try and understand how ecosystems work, and which dynamics might be at play in the face of change… Let’s look at the role of energetics in driving systems

Energetics

•  Available ‘fuel’ in part drives ecosystem structure and function

•  That fuel source can be regulated from the

bottom “bottom up forcing” or from the top “top down forcing”. These pressures can affect ecosystem stability

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

Productivity: rate of that production. Autotrophs or producers

3-11

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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.

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-the unexpected impacts

•  Elk were eating riparian (river) trees and in particular Aspen ‘suckers’ – creating a different (non wooded) habitat

•  Wolves drove Elk up into higher ground (a behavioral modification)

•  The Aspen suckers could now grow – and began leading to more forests

•  *predators can have important effects on their ecosystems

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And finally, even in complex ecosystems with multiple trophic levels such as a rainforest

The result of the creation of ‘islands’ from deforestation. A) has predators such as birds, lizards, spiders (that eat herbivores). B) Without predators – herbivores multiply and decimate the ecosystem. So…are herbivores controlled by food availability or predators…?

Ecosystem change: an example

Killer whales and their appetite for sea otters

Ecosystem change: an example of bottom up effects

• High nutrients=high algal densities • This drives coral cover down • Corals become less competitive, algae gain then upper edge • This is normally a nutrient limited system. The coral reef systems can be profoundly altered

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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What we’ve learned so far… •  Biotic/abiotic •  Tolerance limits •  Habitat fragmentation •  Genetic bottlenecks •  Adaptation

–  Speed –  Effects

•  Trophic energetics – the amount of energy available has important implications for species diversity and trophic levels.

•  Trophic cascades and forcing can have very important effects on ecosystem structure

Now… •  Natural selection •  Speciation – allopatric and sympatric •  Taxonomy •  Adaptation – more •  Species diversity •  Species interactions •  Keystone species •  Populations •  Ecosystem disturbance

Natural selection and adaptation

Populations will adapt and change as their fitness is increased – if some mutation or change leads to greater fitness (ultimately reproductive), it will be passed on, and will prevail in the population. Morphology Physiology Behavior Sexual selection (such as for the mane of a lion, or the beautiful colors of a lekking bird such as a grouse) http://www.youtube.com/watch?v=AAXf4UMYnoI http://www.arkive.org/blue-bird-of-paradise/paradisaea-rudolphi/video-00.html

•  Co-evolution •  Convergent evolution

Function and design

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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

arvulu

s N. tr

ifasc

iatus

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

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

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- 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.

• 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

Speciation: new species evolve, others go extinct

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

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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

Taxonomy


Taxonomy of two common species

3-3

Five Kingdoms

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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 350,000 species

Monarch Butterfly

Blue Jay

Viceroy Butterfly

Batesian mimicry

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Behavioral adaptations

Pitfalls

-  Giraffes

- Polar Bears

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?

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Factors affecting organisms

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

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

Species Interactions (Biotic): Interspecific and Intraspecific

•  Symbiosis •  Competition** - we’ll start here •  Predation/herbivory •  Symbiosis

Adaptation, speciation, and the concept of the niche

Niche The ‘role’ an organism plays in its environment or 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

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Niche partitioning Competition can also lead to niche partitioning – ‘dividing’ up a niche

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?

Types of Symbiosis Symbiosis means ‘living together’ +/+ = mutualism. Both benefit. Often obligatory +/0 = commensalism. One benefits, the other – no effect +/- = parasitism. One benefits, the other is ‘harmed’ or compromised

Zooxanthellae: the key to coral reef productivity

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Cleaning symbiosis: mutualism

mutualism

Commensalism…

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Predation: powerful effects on populations and on evolution 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?

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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

Populations – what affects them? A population is a group of individual organisms

of the same species. What affects one

population may not affect another population of the

same species in a different area…

Reproduction Density Resource availability Disease… Species interactions Birth/death rates

Reproductive strategies

•  K and r selection •  K - selection: few

offspring with high investment

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


Reproductive strategies

3-10

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Sex?

Sexual reproduction •  Introduce new genes •  Diversity in phenotype

and genotype •  Resistance to disease •  Resistance to

environmental change: Adaptation

•  Hard to find a mate •  Picking the right one •  Mutations/problems •  Parental investment? •  Don’t know exactly

what you get

Sex?

Asexual reproduction •  Fast •  Know exactly what

you get •  Can spread your exact

genes •  Cover an area quickly •  No need to find a mate

•  No diversity (easily wiped out)

•  Problem (if one exists) is reproduced

•  Need a self recognition mechanism

Some can do both!

•  Combination of sexual and asexual reproduction can bring the best of both worlds

•  Hermaphrodites: no need to find the right sex! These are organisms that are both sexes at once, or can change from male to female or female to male.

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

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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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The role of ecosystem disturbance

•  Equilibrium and stability: over what time scale do we measure this?

•  ‘Natural’ and anthropogenic disturbance •  Short term and long-term disturbance •  Succession and disturbance: climax

communities? •  What does ‘disturbance adapted’ mean?

Ecosystems and disturbance •  Size, frequency and severity of disturbance are

important

•  Intermediate disturbance model: moderate in frequency and severity - most stable, highest diversity

•  Succession: what will the ecosystem ‘look like’ following a disturbance?

•  Ecosystem disturbance affects community structure, composition, and diversity: RATE and SEVERITY are important


Primary forest succession Figure 3.27

3-14

Stability? Some systems are inherently more stable than others

Resilience – return? Phase (state) shifts

Changed state

Disturbance happens over multiple scales of time, space and severity. Ecosystems respond to this change in a variety of ways. Can we predict it?

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