Transcript species richness - Green Resistance

Welcome back 
• Happy 2011
• Chapter 9 continued; Next chapters
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10, 12, 13, and 14
• Quiz 4 graded – mean: 76%; range: 45 % to 100%
• Next quizzes
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January 14 (9 and 10)
January 19 (12 to 14)
• Your deadlines ?
• Make up classes
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Thursday January 13 – 12.45 to 1.45 pm (Khoury 309)
Thursday January 20 – 12.45 – 1.45 pm (Khoury 309)
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4/11/2016
Homework to all – on the
web
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(1) How do I personally contribute to climate change? (examine your lifestyle — from your diet to your consumption to
your home). Note: To answer this question, you should examine your ‘footprint.’ What is an ecological footprint. As
explained by the Happy Planet Index, “[t]he ecological footprint of an individual is a measure of the amount of land
required to provide for all their resource requirements plus the amount of vegetated land required to sequester
(absorb) all their CO2 emissions and the CO2 emissions embodied in the products they consume. This figure is
expressed in units of ‘global hectares’. The advantage of this approach is that it is possible to estimate the total amount
of productive hectares available on the planet. Dividing this by the world’s total population, we can calculate a global
per capita figure on the basis that everyone is entitled to the same amount of the planet’s natural resources.”
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So, to answer question (1), go to one The Global Footprint Network website
(http://www.footprintnetwork.org/en/index.php/GFN/), and read the information they have, and then you can go to
one of the following sites: The Ecological Footprint Quiz (here), or The Global Footprint Network (and assume we live
in Turkey), or go to the website of the World Wildlife Fund and spend 5 minutes calculating the information (here) – but
keep in mind that that calculation is designed for folks living in the UK so some of the questions won’t apply to you.
There are other sites, of course. The links I provided are a selection of those sites. One other avenue you may use is an
excel sheet to calculate your footprint with more accuracy and detail. Go here:
http://www.google.com/search?client=safari&rls=en&q=ecological+footprint+xls&ie=UTF-8&oe=UTF-8
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(2) What will I actually change in my behavior?
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(3) Assuming I have ultimate power in the world, what new world would I create? What is my vision for a healthier world
— healthier from an environmental perspective, recognizing that the environment cannot be separated from the
economy and from our philosophies.
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Homework
• To all:
• “Me and Climate Change”
• Due January 17
• To those of you who gave Homework 15 to 20%
• Summarize one peer-reviewed article from the
scientific literature on the topic of ‘impact of climate
change on…?’ The article must be NO older than
2007. Include the article with your summary.
• Due January 21
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Top-down or bottom-up?
Why is the world
green?
• Is the world green
because top-down
control predominates
• green plant biomass
accumulates because
predators keep
herbivores in check
Or does the world
taste bad?
• Even if the world is green
(assuming it is), it does not
necessarily follow that the
herbivores are failing to
capitalize on this because
they are limited, top down,
by their predators. Many
plants have evolved defenses
• Herbivores may be
competing and their
predators may be competing
• World is bottom-up
Population and
community
structure and food
web structure
• Are there food web structures that are more stable than others?
• What is stability?
• A resilient vs a resistant community
• Resilient: returns rapidly to former state
• Resistant: little change
• A fragile vs a robust stability
• Fragile: remains unchanged but alters completely
in large disturbance
• Robust: remains roughly the same in the face of
larger disturbances
• Stability: in the face of disturbance
• Disturbance – loss of one or more populations from a
community
Population and
community stability
• Are there particular food webs that are more stable?
• [read box 9.5 to identify what ‘stable’ means]
• Stability: refers to stability in the face of disturbance or
perturbation. What is a disturbance?
• In this case: loss of one or more populations from a community
• What are the effects of such a loss?
• A species that causes a significant effect (like what?) on at least
one other species  strong interactor; keystone species
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Keystone species
• Removal of a keystone species  collapse of the
structure  a community with different species
composition
• Keystone species: “one whose impact is
disproportionately large relative to its abundance”
• Can occur at ANY trophic level
• Lesser snow geese - herbivores that breed in large
colonies in coastal marches; at nesting sites, adult
geese grub fro roots and rhizomes of plants in dry
areas  creating bare areas of peat and sediment 
recovery of those areas is slow
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• Conventional wisdom: increased complexity =
increased stability
• But mathematical models do not support this
argument
• Conclusions differ depending on whether we
focus on individual populations within a
community or on aggregate properties of the
community (such as their biomass or
productivity)
Food webs…
1.
Number of species they contain
2.
Connectance of the web (fraction of all possible pairs of species that
interact directly with one another)
3.
Average interaction strength between pairs of species
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Increases in # of species, increases in connectance, and increases in
average interaction – all tend to decrease the tendency of individual
populations within the community to return to their former state
following a disturbance (resilience)
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Thus – community complexity leads to population instability
• What is found in real
communities – and not in
models?
• Keep in mind that:
• The only communities
we can observe are
those that are stable
enough to exist
• Data on interaction
strength for whole
communities are
unavailable – so assume
contant
• Recent studies:
• Connectance may
decrease with species
number …or…
• May be independent of
species number … or …
• May even increase with
species number
• Conclusion?
• Stability argument does
not receive consistent
support from food web
analyses either
Summary of this chapter
• there are multiple
determinants of the
dynamics of
populations
• Dispersal, patches and
metapopulation:
movement can be vital
factor in determining
and/or regulating
number
• There are temporal
patterns in community
composition
• No predator-prey,
parasite-host or grazerplant pair exists in
isolation
Chapter 10
-- review -• Every population exists within a web of
interactions
• with other populations
• across several trophic levels
• Each population must be viewed in the
context of the whole community
• Populations occur in patchy and inconstant
environments in which disturbance and local
extinction may be common
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…to add…
• Need to appreciate that the world’s biological
diversity is becoming increasingly important
• Need to understand why species richness
varies widely across the face of the Earth
• Why do some communities contain more
species than others? Are there patterns or
gradients in biodiversity? If so, why?
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Species richness…
• The number of species in a community
• Why is it difficult to count or list the species in a community?
• Taxonomic inadequacies
• Only a proportion of the organisms can usually be counted
• Number of species recorded…
• Depends on the number of samples that have been taken or on the volume
of the habitat that has been explored
• But…the most common species are likely to be represented in the first few
samples… more samples -> rarer species will be added
• ? – at what point does one stop taking further samples?
• Until the number of species reaches a plateau
• Species richness of different communities should be compared only if
• They are based on the same sample sizes
• Area of habitat explored
• Time devoted to sampling
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• Number of individuals included
in the samples
Diversity indices
• Species richness
• two communities with ten species…but
• Diversity indices
• Combines both species richness and evenness or
equitability of the distribution of individuals among
those species
• Calculated by determining for each species, the
proportion of individuals or biomass that that
species contributes to the total in the sample
• Diversity then increases with equitability, and for
given equitability, diversity increases with species
richness
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Add to those factors…
• (1) interspecific competition
• If a community is dominated by interspecific competition, the
resources are likely to be fully exploited
• Species richness will then depend on the range of available
resources (specialists and niche overlap)
• (2) predation
• Exerts contrasting effects
• Predators can exclude certain prey species  community can
be less than fully saturated (unexploited resources) 
predation may reduce species richness
• Or predation may keep species below k – reducing intensity
and importance of competition for resources  more niche
overlap and a greater richness of species
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…and other factors…
• Factors that vary spatially
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•
•
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Productivity
Predation intensity
Spatial heterogeneity
Environmental ‘harshness’
• Factors that vary with time (temporal variation)
• Climatic variation
• Disturbance
• Evolutionary age
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Spatially varying factors
Productivity and resource richness
• For plants: productivity of the environment can
depend on most limiting element (nutrient or
condition)
• Animals: broadly speaking, productivity of
environment for animals follows the same trends
as for plants
• Why?
• Due to changes in resource levels at the base of the
food chain
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Productivity and richness
• Expect species richness to increase with productivity
• Supported by an analysis of species richness of trees in North
America in relation to a measure of available environmental energy,
potential evapotranspiration (PET)
• Amount of water that under prevailing conditions would evaporate
or be transpired under a saturated surface
• Water and energy
• Energy: heat and light
• Higher energy inputs lead to more ET and more water
• Southern African trees – species richness increased with water
availability (annual rainfall) but first increased and then decreased
with available energy
• What about animals?
• Animal species richness positively correlated with crude atmospheric
energy
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Productivity and species
richness
• Why?
• Not sure… but
• For an ectotherm (eg – a reptile) – extra atmospheric
warmth  increase intake and use of food resources
• For an endotherm (eg – bird) – extra warmth  less use
of resources in maintaining body temp and more
resources for growth and reproduction
• In both cases  faster individual and population growth
 larger populations
• Warmer environments might -> allow species with
narrower niches to persist and such environments may
support species
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Productivity and species
richness
• May also be a direct relationship between
animal species richness and plant productivity
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• Strong positive
correlations between
species richness and
precipitation for both
seed-eating ants and
seed-eating rodents;
more species of very
large ants and very
small ants. Why?
• Species richness of fish
also increases with
lake’s phytoplankton
productivity
• Note: increase in
production does not
always lead to increase
in diversity
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Predation intensity
• Predation may increase richness
• By allowing competitively inferior species to coexist
with their superiors (predator-mediated
coexistence)
• Predation may reduce richness
• Intense predation may drive prey species to
extinction
• Overall: predation intensity and species richness:
humped relationship
• Greatest richness at intermediate intensities
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• Removed
starfish from
an 8 m long
and 2 m deep
shoreline
• Other species
became
dominant
(barnacles
and then
mussels)
• Later –
reduction in
species
richness
• Predatormediated
coexistence
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Wolves…
• The gray wolf was reintroduced to Yellowstone National Park in
the spring of 1995, after a 70-year absence. In the past 6 years,
the population has grown from 31 released animals to more than
100 individuals, as wolves have exploited an abundant elk
population. Consequently, elk that had previously experienced
significant mortality primarily in the late winter because of
starvation now face mortality throughout the year. When an elk
is killed by wolves, its carcass is partially consumed by the wolves
and then is scavenged extensively by eight other carnivore
species (coyote, bald eagle, golden eagle, grizzly bear, black bear,
raven, magpie, and red fox) and less intensely by up to 20 other
species. Field observations indicate that the infusion of wolf-killed
ungulate carrion throughout the year has created an abundant
and dependable food source for these other carnivores.
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Spatial heterogeneity
• Environments – more heterogeneous – more potential
for species richness. Why?
• Some studies: positive relationship between plant
diversity and heterogeneity
• Substrate…slope… drainage … soil pH
• Most studies: related species richness of animals to
structural diversity of plants in their environment
• Due to experimental manipulation of plants
• Or through comparisons of natural communities that
differ in plant structural diversity
• Or plant species richness
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Environmental harshness
• Environments dominated by extreme abiotic factor (harsh environments) more difficult
to recognize than apparent
• Anthropocentric view. What is cold for us might seem benign to a penguin
• ‘let the organism decide’ harshness factor
• Environment extreme – if organisms, by their failure to live there, show it to be so.
Circular definition.
• Environment extreme: one that requires, of any organism tolerating it, a morphological
structure or biochemical mechanism that is not found in most related species and is
costly, either in energetic terms or in terms of the compensatory changes in the
biological processes of the organism that are needed to accommodate it
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Example: plants living in highly acidic soil (low pH). Need specific structures/mechanisms
• Harsh environments: low species richness
• Hot springs. Caves. Highly saline water (Dead Sea)
• Each also categorized by low productivity and low spatial heterogenity
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Temporally varying
factors
• Climatic variation
• Is the variation predictable? (relative time scales) …
• temporal niche differentiation
• Opportunities for specialization in a non-seasonal environment
• Is the variation unpredictable? – climatic instability
• Could increase species richness …or not
• Does species richness increase as climatic variation decreases?
• Disturbance
• Environmental age: evolutionary time
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Temporally varying
factors
• Disturbance
• Reminder: In a dominance-controlled community 
community succession
• Very frequent disturbances: keep most patches in early stages
of succession (few species) + rare disturbances allow patches
to be dominated by best competitors (few species)
• Conclusion: intermediate disturbance hypothesis
• All communities are subject to disturbances that exhibit different
frequencies and intensities
• Environmental age: evolutionary time
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Temporally varying
factors
• Environmental age: evolutionary time
• Communities may differ in species richness because some are closer
to equilibrium and therefore more saturated than others
• Some argued that tropics are richer than temperate in part because
tropics have existed over long and uninterrupted periods of
evolutionary time (temperate regions – recovering from glaciations)
• But tropical areas were also disturbed during the ice ages by associated
climatic changes that saw tropic forest limited to a small number
surrounded by grassland
• Another explanation: species evolve faster in the tropics because of
higher rates of mutation in these warmer climes
• Rates of evolution of woody plant species twice as fast in the tropical
species
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Gradients of species
richness
• Habitat area and remoteness: Island
biogeography
• Latitudinal gradients
• Gradients with altitude and depth
• Gradients during community succession
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Island biogeography
• Number of species on islands decreases as island area
decreases. Species-area relationship
• What is an island?
• Islands of land in a sea of water
• Lakes - Islands in a sea of land
• Mountaintops – high altitude islands in a low altitude
ocean
• Gaps in a forest canopy – island in a sea of trees
• Islands of particular geological types, soil types, or
vegetation types
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Start here Island
biogeography
• Species-area relationships: one of the most
consistent of all ecological patterns
• Is the impoverishment of species on islands more
than would be expected in comparably small areas of
mainland?
• Why do larger areas contain more species?
• Encompass more different types of habitat – not
enough of an explanation
• Island size and isolation: number of species on an island
determined by a balance between immigration and
extinction; this balance is dynamic; and extinction rates
may vary with island size and isolation
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Island biogeography
1.
The number of species on an island should eventually
become roughly constant through time
2. This should be a result of continual turnover of
species, with some becoming extinct and others
immigrating
3. Large islands should support more species than small
islands
4. Species number should decline with the increasing
remoteness of an island
- MacArthur and Wilson’s theory’s predictions
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Latitudinal gradients
• Increase in species
richness from the
poles to the tropics
• Why?
• No clear explanation.
• Latitudinal gradient
intertwines
components
previously
discussed…
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Gradients with altitude
and depth
• Decrease in species richness with altitude – akin to
that observed with latitude - -in terrestrial
environments
• Other studies: increase with altitude; other
studies: hump-shaped patterns
• Productivity and temperature? Productivity and
growing season? Stress with extremes?
• In aquatic environments: change in species
richness with depth strongly similar to terrestrial
gradient with altitude
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• Skip – patterns in taxon richness in the fossil
record
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Summary
• Richness and diversity
• Climatic variation
• Productivity and
resource diversity
• Disturbance
• Environmental age
• Predation intensity
• Island biogeography
• Spatial heterogeneity
• Gradients in species
richness
• Environmental
harshness
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