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Chapter 44 Ecological and Evolutionary Consequences of Species Interactions
Terms:
Interspecific interaction – interactions between members of different species
Intraspecific competition – competition among members of the same species
Interspecific competition – competition between members of two or more species
Limiting resources – something required by an organism is in the shortest supply relative
to demand
Resources partitioning – a situation in which selection pressures resulting from
interspecific competition cause changes in the ways in which the competing species use the
limiting resource, thereby allowing them to coexist
Symbiosis – the living together of two or more species in a prolonged and intimate
relationship
Mutualism – a type of interaction between species that benefits both species (+/+)
Commensalism – a type of interaction between species in which one participant benefits
while the other is unaffected (+/0)
Parasitism – one species benefits at the cost to another (+/-)
Amensalism – interaction in which one animal is harmed and the other is unaffected (-/0)
Extinction – the termination of a lineage of organisms
Invasive species – an exotic species that reproduces rapidly, spreads widely, and has
negative effects on the native species of the region to which it has been introduced
Questions:
1. Interspecific competition (-/-) is competition between two species for resources. This
interaction negatively affects the per capita growth of both species. Consumer-resource
interactions occur when one species consumes the other for nutrition. This interaction negatively
affects the per capita growth of the eaten species, and it increases the per capita growth of the
predator. A mutualism (+/+) is an interaction that benefits both species. Commensalism (0/+)
benefits one species and doesn’t affect the other. Amensalism (-/0) negatively affects one species
and is neutral for the other.
2. Competition is an interaction in which animals use the same resources. Once an
animal uses a resource, it is unusable for other animals, so animals must compete for these
resources. Interspecific competition is competition between two different species; whereas,
intraspecific competition is competition between members of the same species.
3. A limiting resource is a resource required by an organism that is in short supply.
Limiting resources inspire interspecies completion. Resource partitioning is a situation where
selective pressure from interspecific competition causes a species to change so that the two
competing species can co-exist; however, resource partitioning can inspire intraspecific
competition.
4. Predation is when organisms gain their nutrition by eating other living organisms. The
consumer benefits; while, the prey dies. Evolutionarily the consumer and resource are at odds
with one another. While, the resources adapt various defense strategies, the consumer will favor
traits that help it obtain the resources.
]5. Mutualism is when both interacting species benefit. Ex: Pollinators and flower.
Commensalism is when one species benefit from an interaction, while the effect on the other
species is neutral. Ex: Cattle convert plants to dung which beetles use.
Amensalism is when one species is harmed from an interaction, while the effect on the other
species is neutral. Ex: when elephants walk through forests they crush bugs on the forest floor
Parasitism is when an organism feeds off a host. This negativity impacts on the host as it benefits
the parasite. Ex: tapeworms can feed off humans
6. The Kangaroo rats negatively affected the grasses abundance in years of drought, and
in years of rainfall, the rats had a positive effect on the per capita growth. When there was an
abundance of seeds, more likely found in a year of rainfall, the rats leave their stored seeds in the
ground. However, when the seeds are sparse, they eat all the seeds, and they don’t leave any in
the ground.
7. Selective pressures can cause one species to be favored in resource partitioning. Some
species can be adapted to obtain a resource or protect a resource more readily in different
environments. This competition for available resources causes different species to thrive in
different environments; while other have higher densities in different environments.
8. In an environment where one trait is favored over another, the species with that trait
would be favored, and they would have an increased fitness. Also, the competition might cause
natural selection to favor a certain trait within a species.
9. Mimicry can but used by an organism to mimic other unpalatable species so predators
avoid them. For example, passionflower leaves have raised yellow bumps to resemble the eggs
of the zebra butterflies, whose caterpillars eat the leaves. Since the butterflies don’t lay their eggs
on leaves that already have eggs, these egg-like bumps protect the plant from being eaten.
10. A species becomes invasive if it is introduced in an environment where it can thrive
without any natural enemies. If the species reproduces and spreads quickly, it can become highly
dense in some areas. Invasive species often harm the natural cycle of environments. For
examples, in the 1800s when purple loosestrife was introduced to North America, it took over
the wetlands of the USA. Now it competes for pollinators with other plants, and these other
plants, like Lythrum alatum, are receiving less pollen each year and are reproducing less.