Ecology Chapter 12 ECU
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Types of Interactions
- Competition (-,-)
- Predation (+,-)
- Herbivory (+,-)
- Parasitism (+,-)
- Mutualism (+,+)
- Commensalism (+,0)
Competition occurs between species that share the use of a resource that limits --------------------- of each species
the growth, survival, or reproduction
Competition, whether direct or indirect, can limit the ------------- of competing species.
distributions and abundances
Concept 11.3: Competing species are more likely to coexist when they in different ways.
Concept 11.4: The outcome of competition can be altered by (4)
environmental conditions, species interactions, disturbance, and evolution.
Interspecific competition is an interaction between two species in which each is harmed when they both
use the same limiting resource.
Intraspecific competition can occur between individuals of
a single species
features of the environment that are required for growth, survival, or reproduction, and which can be consumed to the point of depletion :
Physical factors affect population growth rates but are not
consumed or depleted.
Species compete indirectly through their mutual effects on the availability of a shared resource. Competition occurs simply because individuals reduce the availability of a resource as they use it. (e.g., pitcher plants, diatoms)
Species compete directly for access to a resource, antagonistic actions (e.g., two predators fight over a prey item, voles aggressively exclude other voles from preferred habitat).
interference competition in which individuals of one species release toxins that harm other species.
a group of organisms that use similar resources in similar ways; individuals that exhibit similar habitat requirements and that respond in a similar way to changes in their environment
Species use a limited resource in different ways
Possible outcomes of competition
- 1) Coexistence
- 2)Competitive exclusion
Competition is an important driving force for:
- Niche separation
- Niche specialization
- Niche diversification
Natural selection can influence
can influence the morphology of competing species and result in character displacement
Concept 12.1: Most predators have broad diets, whereas a majority of herbivores have
relatively narrow diets.
Concept 12.2: Organisms have evolved a wide
range of adaptations that help them
capture food and avoid being eaten.
Concept 12.3: Predation and herbivory affect ecological communities
greatly, in some cases causing a shift from
one community type to another.
Concept 12.4: Population cycles can be caused by feeding relations, such as a three-way interaction between
predators, herbivores, and plants.
Surrogate Measures of Fitness
Life changed radically with the appearance of the ------------- roughly 530 million years ago.
first macroscopic predators. Before that time, the seas were dominated by soft-bodied organisms.
Physical defenses include (3)
large size (e.g., elephants), rapid or agile movement (gazelles), and body armor (snails, anteater).
Other species contain toxins. They are often brightly colored, as a warning—------------------. Predators learn not to eat them
---------------------the prey is camouflaged, or resembles its background.
Other prey species use mimicry as a defense.
resemble another species that is fierce or toxic; predators that have learned to avoid the toxic species will avoid the mimic species as well.
Sometimes there is a trade-off between behavioral and physical defenses example
snails that are more easily crushed (long and thin) often can sence and are quicker to escape predators
Some produce huge numbers of seeds in some years and hardly any in other years (called
masting). The plants hide (in time) from seed-eating herbivores, then overwhelm them by sheer numbers.
growth responses that allow the plant to compensate for, and thus tolerate, herbivory. Removal of plant tissue stimulates new growth.
Percent of comsumption in which overcompensation can not overcome predation
A region of plant tissue consisting of actively dividing cells forming new tissue.
the ability of a cell to give rise to unlike cells and so to develop a new organism or part
Plants that have evolved WITH herbivores can demostrate
The timing of herbivory (predation on the plant) affects
the compensation abilities of the play. Early herbivory can increase the plants fitness, however late herbivory is negative as there aren't enough resources for effective compendation
Plants have an array of structural defenses, including (4)
tough leaves, spines and thorns, saw-like edges, and pernicious (nearly invisible) hairs that can pierce the skin.
Secondary compounds are
chemicals that reduce herbivory. Some are toxic to herbivores, others attract predators or parasitoids that will attack the herbivores.
Induced defenses are stimulated by
herbivore attack. This includes secondary compounds and structural mechanisms. Example: some cacti increase spine production after they have been grazed on.
Problems with Direct Defense
1) herbivorous insects rapidly evolve resistance to these defenses, which 2) allows the insects to sequester plant defenses and use them for their own defensive purposes; and 3) many direct defenses slow herbivore growth or digestive efficiency, causing insects to eat more plant material, rather than less, to complete their life cycles.
signals that help predatory bugs find their prey, the hawkmoth larvae
For any defense mechanism of a prey species, there is usually a predator with
a countervailing offense.
Improvement in defense adaptions exert strong selection pressure on
predators and herbivores.
The garter snake, Thamnophis sirtalis, is the only predator known to eat
the toxic rough-skinned newt.
All exploitative interactions have the potential to reduce the (3)
growth, survival, or reproduction of the organisms that are eaten.
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