Download Lecture 37 - Ecology - Chapter 46 Niche Community

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Lecture 37 - Ecology - Chapter 46 Some basic concepts in chapter 45 apply to the next few lectures, so please read it.
How organisms interact with each other and the environment
•  Based on the molecular biology, cell biology, physiology, and
behavior of animals.
•  Includes emergent properties that cannot be understood by a
reductionist understanding of the biology of individual species:
–  “The whole is greater than the sum of its parts”.
•  Since we do not even fully understand the mechanisms
underlying the biology of individual organisms, ecological
processes are almost always studied in the absence of
mechanistic understanding
Niche
Niche:
–  The entire range of biotic and abiotic interactions of members of
one species with all others in its usual habitat, as well as with the
abiotic features that facilitate the existence of a species in that
usual habitat.
–  Sum total of all activities and relationships which individuals of a
species engage in as they secure and use the resources required to
survive and reproduce.
Fundamental niche:
–  Widest range of abiotic and biotic situations a species could
occupy
Realized niche:
–  The niche a species actually occupies, given constraints of
competition with other species
Community •  All the species that live together in a
habitat
•  The habitat shapes a community’s
structure
–  Climate and topography
–  Available foods and resources
–  Adaptations of species in the
community
–  Interactions between species in the
community
–  Arrival and disappearance of species –  Physical disturbances
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Interactions Between Species
•  Neutrality –  Most common type of interaction
•  Competition
–  Interspecies competition is harmful to both species
•  Symbiosis
–  Commensalism •  Helps one species and has no effect on the other
–  Mutualism
•  Helps both species
–  Parasitism
•  Harms one species for benefit of the other
•  Predation
Competition
•  Most interactions between members of the same species are
competitive.
•  Closely related species are clearly more likely to compete
with each other than distant or unrelated species.
•  The Principle of Competitive Exclusion: –  If two species occupy exactly the same niche, one of them will
become extinct in areas occupied by both
–  Therefore, if 2 similar species seem to coexist in the same
niche, they must actually have somewhat different
requirements
•  E.g.: eating different size seeds, selecting flowers of different
shape or color
•  Harms one species for benefit of the other
Competition between 2 species of Paramecia that occupy identical niches
Partitioning Resources
Paramecium caudatum
•  If two species appear to share
the same niche, and neither
drives out the other, they are
somehow dividing the resources
so that, in actuality, they have
different realized niches.
White
Black
•  Black and white rhinoceros
Paramecium aurelia
–  Inhabit same area -- African
savannah and appear very
similar
–  Mouths differ
•  White rhinoceros has wide, flat
mouth, eats grasses
•  Black rhinoceros has narrower
mouth with extended upper lip,
browses on branches & herbs
Their names have nothing to do
with their color! Both are grey.
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Plants partitioning prairie soil with roots of different lengths
Partitioning Niches
(continued)
• Insects
– Several species may live off a single plant
species, especially when the insect has
overcome chemical defenses of a plant
– One insect species may eat leaves; another
seeds; a third, flowers: partitioning
resources
For the local toxic milkweed
plants, butterflies (B) lay their eggs
on the leaves which their
caterpillars eat, while bugs (F) lay
their eggs on the flowers and their
larvae eat the developing seeds.
Demonstrating Interspecies Competition: Exclusion Experiments
•  Two closely related species in the same habitat
•  Fence plots, excluding one species or the other
•  Observe alterations in Bristly
foxtail
Indian
mallow
Smartweed
•  Symbiosis:
–  Living together for at least some part of the life cycle,
typically two quite different kinds of organism
•  Commensalism
•  Mutualism
•  Parasitism –  plant growth
–  effects on numbers of remaining species
•  Conclusion:
–  greatest competition is between closely related species
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Commensalism
•  Interaction between species that helps one of the species, and
neither harms nor helps the other
•  Examples
–  Birds roosting in trees
–  Orchids growing on trees
–  Most of our gut bacteria?
Mutualism
•  Both species benefit
–  Species very different from each other
–  Plant/animal interactions are common
•  May be obligatory
–  Yucca plants and yucca moth (right)
•  Each yucca species has its own moth species
–  Mycorrhizal fungi and plants
•  Orchids require these fungi to grow
–  Termites and protozoa in gut
•  Allow termites to eat wood
–  Ants nest in plants
•  Protection from herbivores
•  Some are more flexible
–  Honeybees
•  Gather nectar from many species
•  Efficiency of pollination also varies
–  Several species of insects may pollinate a species of flower
Extreme mutualisms
•  Lichens are combinations of fungi with
either a photosynthetic bacterium
(cyanobacterium) or an alga (usually a
green alga)
•  Most corals have obligate symbiotic
photosynthetic bacteria living with them.
Thats why most corals (except the deep
sea variety), are in shallow water and
colorful. “Bleaching” of corals is loss of
their colorful photosynthetic partner and
death.
•  Once again, mitochondria (all
eukaryotes) and chloroplasts (in plants)
result from endosymbiotic bacteria.
Parasitism
• Parasites drain nutrients from their hosts and live
on or in their bodies.
• Almost ubiquitous feature of animal life
• Parasites on animals include
– Viruses, Bacteria, Protists, Fungi
– Invertebrates: – Nematodes, Platyhelminths, Insects
– Vertebrates:
– cuckoos, cowbirds
Adult roundworms in pig intestine
• Parasites on plants include other plants
– Mistletoe
• There are very few parasitic Archaebacteria or
Archaea, and only parasitic on other Archaea
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Parasitoids
Predation and Population Cycles
•  Unlike parasites, parasitoids do kill their hosts, eventually
•  Most typically: insects, e.g. many wasps, some flies
– Lay eggs on host, which is usually another insect
•  Larvae feed on host
•  Major method of biocontrol of insects, especially for Lepidoptera Parasitoid pupae emergent
from a caterpillar host
•  Predators: •  In single predator/prey
–  feed on other living organisms
interactions
–  free-living - do not take up
–  Oscillations between
residence on their prey
population densities
–  Prey populations rise
–  Predator populations
follow
–  Prey populations crash
–  Predator populations
follow
•  Example:
–  Canadian lynx and
snowshoe hare
Ichneumon wasp
Canadian Lynx and Snowshoe Hare
•  Note on graph: –  cyclic oscillations
–  lynx are scarcer than
hares
•  Krebs studied populations
for ten years
•  Fencing plots delayed cyclic
declines but didn’t eliminate
them
•  More complex three-level
model yields better fit
–  Aerial predators, plant
abundance also involved
Coevolution between Predators and Prey
•  Close interaction between 2 species may exert selection pressure on
each, leading to alterations in both and an arms race
–  As snail shells thickened, claws of snail-eating crabs became more
massive
–  Cheetah and its antelope prey are both extraordinarily swift runners
–  Plants produce toxic substances, insects detoxify them and sometimes
not only live off the toxic species, but use the plant toxin as a defense for
themselves.
Canadian lynx (dashed line)
Snowshoe hares (solid line)
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Predator-Prey
Adaptations
• Toxic defense systems
and aposematic coloration
– Species that feed on toxic
plants and sequester the toxin
are often brightly colored.
– Color warns predator not to
attack
• Cryptic coloration
– Camouflage
– Also used by predators
• Monarch butterfly
– Toxic defense systems • Mimicry
–  Harmless species mimics color pattern of toxic or dangerous species
Yellowjacket
Beetle
Syrphid fly
Community Stability
Community •  All the species that live together in a
habitat
•  The habitat shapes a community s
structure
–  Climate and topography
–  Available foods and resources
–  Adaptations of species in the
community
–  Interactions between species in the
community
–  Arrival and disappearance of species –  Physical disturbances
Non-stinging wasp
•  Eastern US communities include
–  Forests
•  Climax forests may be stable for centuries
–  Savannahs
•  Mix of grasses and sparse trees
•  Quasi-stable in the presence of periodic fires
•  Trees dominate if fires are suppressed
–  Prairies
•  Highly diverse
•  Very stable before Europeans came
•  Require fires to remain tree-free
•  Even stable communities may oscillate between species
•  In general, diversity increases community
stability
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Successional Cycles
Secondary succession from corn field
20 years
•  Disturbed communities change over time
•  Primary succession occurs when plants first move into entirely new habitats
–  New volcanic islands, e.g. ferns first
•  Secondary succession occurs after a volcanic explosion or a
fire
–  Mount St Helens in 1980
–  Yellowstone fires in mid-1990s
•  Fireweed, grasses are first
•  Seeds of some conifers germinate only after a fire
Destabilizing communities
•  Even climax communities can be
destabilized by
–  Loss of crucial species
Wolves and beavers in Yellowstone
–  Exotic species
•  Australia
–  Rabbits, cane toads
•  Hawaii
–  Pigs, goats, wasps
•  US
–  Kudzu in the south
–  Dutch elm disease
–  Zebra mussels
–  Other human intervention
•  Plowing the prairie
•  Draining wetlands
Island Biogeography
•  The number of species likely to be found in a given area depends on
–  Size of the area
•  The number of species increases with the size of the area
•  Or: Area is directly proportional to species number –  Distance from sources of species
•  The farther the distance from the colonizing source, the fewer
species are found on the island
•  Or: Distance is inversely proportional to the number of species
•  Theory developed for true islands
•  Also holds for conceptual islands
–  Wilderness parks in a farmed area
–  Natural areas in disturbed setting
•  Prairie remnants in Illinois
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