Download inter-specific-relationships-information (1)

INTER-SPECIFIC RELATIONSHIPS – Information and Worksheet
In an ecosystem, there are two sorts of interactions between different organisms:
1. INTRA-SPECIFIC interactions, between members of the same species. For instance a pack of 6
hyaenas might all squabble and fight over a dead carcass of an antelope. The hyaenas are all the
same species - indeed the other hyaenas with which s/he fights may even be brothers and sisters.
2. INTER-SPECIFIC interactions, between individuals of different species. In this case lions and
hyaenas may be fighting over the same dead carcass.
Interspecific interactions are interactions among organisms of different species. Typically, these
interactions are classified based on whether they BENEFIT one or both of the species involved or whether
they HARM one of the species involved.
(Sometimes the word SYMBIOSIS is used to describe inter-specific interactions but it is best to avoid using
that word because often it is used, in error, when people really mean mutualism.)
Types of INTERSPECIFIC interactions
Predation
When a larger animal eats other, smaller animals. Lions
may eat buffalo, and wolves may eat deer. Spiders, like
the orbweaver, capture and eat insects in their webs. The
predator benefits but obviously the prey is harmed.
Mutualism
A relationship between two species where both benefit.
The yucca moth both pollinates and feeds on the yucca
plant; acacia ants live in the thorns of, defend, and are fed
by the acacia tree in which they live; and trees can’t get
along without mycorrhizae living in/on their roots and
absorbing food for them. Many plants and their
pollinators have evolved mutualistic relationships.
Butterfly-weed provides food for and is pollinated by butterflies like pipevine
swallowtails.
Commensalism
A relationship between two species that is beneficial to
one but neither benefits nor harms the other. Cattle
egrets follow cattle to feed on the insects stirred up by the
grazing cattle. (Might there be a benefit for the cattle?)
Parasitism
Parasitism occurs when a smaller organism feeds on a
larger, weakening or killing it. This is a relationship where
one organism benefits and the other is harmed. Often the
host is not killed outright. Because a parasite lives in/on the
body of its host and needs the host to remain alive, it is
usually advantageous for the parasite to not kill its host.
Humans and domestic animals are occasionally infected
with or bothered by tapeworms and roundworms (endoparasites) and mosquitoes
and leeches (ectoparasites).
Competition
Two species challenging each other for the same resource
(often food) is called competition. In this sort of
interaction, both species are harmed - one species may
lose the competition and be driven away, but the winner
has used up a lot of energy and may be injured in the
challenge. Lions and hyaenas might challenge for a dead
antelope; the hyaenas may be the 'winners' but have
probably suffered too.
Neutralism
In this interaction, neither species involved apparently gains any benefit and neither
is harmed. So for instance in a grassland, you may find frogs and deer and rabbits all
feeding together in the same place but in no way interacting with each other. This
then is the most common of interactions but surprisingly many ecologists argue that
this interaction never actually exists. They argue that there will always be some
relationship. Maybe the deer create little paths with their feet so that the frogs and
rabbits can more easily move around? All three fertilise the grassland with their
excrement, which therefore benefits all of them. Maybe the rabbits eat the grass
shoots which the deer prefer. Who knows?
So .... a summary
An inter-specific interaction is a close ecological relationship between the individuals of two (or more)
different species. These interactions can always be looked at in terms of benefits and harms.
Mutualism
-- both species benefit
Commensalism -- one species benefits, the other is unaffected
Parasitism
-- one species benefits, the other is harmed
Competition
-- neither species benefits, both in a sense, are harmed
Neutralism
-- neither species is harmed or benefited
To simplify things, ecologists often only use the signs +, 0 or - to describe inter-specific interactions. The
following table illustrates the correct use of these terms in interactions between two species: Species "A"
and Species "B".
"+" denotes BENEFIT to the species
"0" denotes neither harm nor benefit
"-" denotes HARM to the species
SPECIES A
+
Parasitism
0
-
Commensalism
Mutualism
Neutralism
Competition
-
0
SPECIES B
+