An Interactive Introduction to Organismal and Molecular Biology, 2021

82 | SPECIES INTERACTIONS
Two-Species Interactions
Community ecology includes the ways in which species interact. Research sometimes focuses on two species of
a complex community and the general ways those species interact with one another can be classified by whether
the species are positively, negatively, or neutrally impacted. The following video describes the main types of
species interactions, with examples. The table below summarizes these types.
An interactive or media element has been excluded from this version of the text. You can view it
online here:
https://openbooks.lib.msu.edu/isb202/?p=199
Interaction Definition Species A Species B
Mutualism*
Commensalism*
Consumption
· Parasitism*
· Parasitoidism*
· Predation
· Herbivory
Competition
A long-term, close
association between two
species in which both
partners benefit
Organisms of two species
use the same limited
resource and have a
negative impact on each
other
One species eats all or
part of the body of a
member of another
species. The consumed
species is either killed
from the interaction
(e.g., predation) or
harmed but likely
survives (e.g., parasitism)
Two species “fight” over
a resource. Although one
species may “win,” it is
still negatively impacted
by taking part in the
competition
+ +
+ N
+ –
– –
*These interactions may also be labeled as symbiotic interactions (i.e., symbiosis) if the two species live and
interact closely together.