Download Evolution notes lecture Interactions between populations Fall 2013

Interactions between populations
Evolution Biol. 4974/5974
D. F. Tomback
Interactions Between
Populations and Species
Biol 4974/5974
Evolution
Learning goals
Know and understand:
• The basic ecological interactions between one or more
populations or species that lead to evolution.
• How species exert selection pressure on other species in
ecological interactions.
• The three evolutionary consequences of competition:
Resource partitioning, character displacement, and
competitive exclusion.
• The evolutionary consequences of predator-prey relationships.
• The kinds of mutualistic interactions, and the evolutionary
consequences of mutualism.
Basic interactions
Basic ecological interactions between populations that can lead
to evolution:
• Competition
• Predation
• Symbiosis and mutualism
These interactions can be affected by relative population sizes of
species, which change over time. Many of these interactions
are coevolutionary—each species exerts selection on the other.
Fig. 20.1B Fluctuations
in populations of the
Great Tit in Holland
between 1912 and 1943.
1
Interactions between populations
Evolution Biol. 4974/5974
D. F. Tomback
Outcomes of competition
Resource partitioning: When two species or more species
compete for the same resources, they evolve to specialize in
foraging to minimize competition.
Fig. 20.1 a
Character displacement: Resource
partitioning can lead to changes in morphology
related to foraging. (Grant, P.R. 1986)
• Beak dimensions reflect range of resources
available.
• They will change as resources shift.
Fig. 20.2
Outcomes of competition
Competitive exclusion: The Competitive Exclusion Principle
states that no two species can coexist indefinitely when the
same resource limits both species.
• This implies that two species cannot occupy the same ecological niche.
• Study reveals that for similar species there are often subtle differences that
allow them to coexist.
• E.g., work of G. F. Gauss on two species of Paramecium in the laboratory.
Fig. 20.3
2
Interactions between populations
Evolution Biol. 4974/5974
D. F. Tomback
Predation overview
Predation describes the foraging behavior
of consumers—i.e., predators.
--animals catching and eating other animals
for food.
But, predation is also used in a general
way:
• Herbivores consume plant parts, such as
leaves or stems.
• Granivores are “seed predators,”
because they consume seeds.
• Parasitoids are insects that lay their eggs
in host organisms, which are consumed
alive by larvae.
• Parasites consume tissue or nutrients
from living hosts.
www.thebigzoo.org
USFWS: snowy owl
Predation overview
Ecuadorian stick insects
www.insects.org
Predators have morphology and behavior
adapted to catch prey. Their teeth and
digestive tracts are adapted to their prey.
• E.g., cheetahs run fast.
• E.g., spiders weave webs.
Prey species are adapted to avoid predators.
• Cryptically-colored (use camouflage)
• Mimic surroundings
• Travel in large groups; have acute senses.
Plants and seeds are adapted to discourage
herbivores.
• May have chemical compounds that deter
predators (e.g., tannins in acorns).
• Deter herbivores with tough leaves,
thorns, or prickles.
www.waynesword.palomar.edu
Predator-prey cycles
Close dependence of predator and prey, e.g., snowshoe hare-Canada lynx
interaction.
• The prey is a partial cycle ahead of the predator cycle.
• Evolutionary “arms race”.
R.E. Ricklefs. 2008. The
Economy of Nature, 5th
ed.
3
Interactions between populations
Symbiosis and mutualism
Symbiosis: Close physical association between
species, usually coevolved.
Trophic mutualism: Species evolved to share
energy and nutrients.
• lichens: fungi and cyanobacteria (symbiosis).
• leaf cutter ants: ants and fungi.
• Rhizobium and root nodule plants: nitrogenfixing association (symbiosis).
Defensive mutualisms: One species receives food
or shelter from the other species; in return, it
defends the partner against predators, herbivores,
or parasites.
• Cleaning symbioses: “cleaner” shrimp and
“cleanee” fish in the tropics
• Acacia-ants and ant-acacias: ants defend the
plant and obtain food and shelter (neotropics).
Evolution Biol. 4974/5974
D. F. Tomback
Figure 20.14
www.waynesword.palomar.edu
Mutualism
Dispersive mutualisms: Involve
pollination or seed dispersal
mutualisms.
• Hummingbirds pollinate plants:
Some relationships are very general
and some specialized (tropical).
• Yucca moth and yucca plant: Female
moths carry pollen, enter a flower,
cut ovary with ovipositor and deposit
1-15 eggs; deposit pollen on stigma
to set seeds as food for larvae. Loss
of seeds <30%. Obligate.
• Clark’s nutcracker and whitebark
pine: Cones do not release seeds;
nutcrackers harvest seeds and cache
them in the ground for future food;
remaining seeds germinate and
produce seedlings.
Figure 20.16
Study questions
• What are the three ecological interactions between
populations that can lead to evolution?
• These interactions can be coevolved—what does that
mean?
• Competition as a process can result in resource partitioning,
competitive exclusion, or character displacement. Explain
how these outcomes result from evolutionary interactions.
• How is the concept of predator used to refer to consumer
interactions?
• Explain how predators and prey may coevolve in an
evolutionary “arms race.”
• Explain how mutualists may coevolve together. What are
the different categories of mutualism?
4