06 - Species Interactions

Community

interacting populations of different species found in same place/time, interrelationships govern flow of energy and nutrient cycling within community

niche

combination of the physical habitat of a species and its ecological role in that habitat, determined by both abiotic and biotic factors that affect the species.

Fundamental niche:

Full range of climatic conditions and food resources that permits a species to survive (absence of interactions with other species)

Realized niche

Species niche in the presence of negative species interactions (interspecific competition or predation), and positive species interactions (mutualisms or commensalisms)

which niche includes range of climatic conditions and food resources

that permits a species to survive

both

The focus of Hutchinson and colleagues

negative species interactions

fundamental vs realized niche - negative interaction

Many species have smaller realized niches because of interactions

with other species that can limit where they can exist indefinitely

fundamental vs realized niche - positive interaction

Positive interactions with other species can expand a species’ range within its fundamental niche, allowing it to exist in areas where it might otherwise struggle to persist

Some positive interactions can even allow a species to persist in

areas where they would otherwise not survive at all!

Phylogenetic niche conservatism

similarity in aspects of the niches

of closely related species due to their shared evolutionary history

Competition

When individuals use the same limiting resource in the same way – resulting in lower fitness for both (-/-)

types of competition

Exploitation

Interference

Exploitation

(resource competition) – when one competitor

consumes a shared resource that limits its and other species’

growth, making it less available for others to use (two

competitors only interact indirectly)

first come typa shi

Interference

(contest competition) – when one species

restricts another species’ access to a limiting resource, which

can involve antagonistic interactions or one species excluding

the other from a space (two competitors directly interact)

even fight

competition classification based on relatedness

intraspecific

interspecific

Intraspecific competition –

competition among individuals of the same species

can be classified as exploitation or interference

density dependant (comp for resources )

Interspecific competition–

competition between

individuals of different species

can be classified as exploitation

or interference

R* rule

when two species compete for a single limiting resource (at constant population densities) the species that can persist on lower amounts of that resource will win the competition.

Amensalism

when one species is not affected by competition

(it ‘wins’ outright), e.g., kudzu

Competitive exclusion principle

two or more species cannot coexist indefinitely while using a single, relatively scarce, resource in the same way

might lead to a shift in the week competitior

competitor species can coexist if

1. stronger competitos are kept in track by pradators

2. Competitor species can divide up shared resources

3. Regular disturbances can reduce population sizes of better

   competitors

4. Resources can vary, favouring different competitors

5. Weaker competitors can benefit from positive interactions

   with a third species

Predator-mediated coexistence

predation can reduce number of

dominant competitors, leading to coexistence with lesser

competitors it would otherwise exclude

Character displacement

– divergence in characteristics

of two otherwise similar species as a result of

competition in sympatry

eg darwin finches

Predation

when one individual benefits (gains resources) by

consuming part, or all of another organism (+/-)

different types of consumption

tru predation

grazing

parasitism

‘True’ predation –

one organism consumes another organism

(prey die quickly, many prey are attacked over predator’s lifetime)

can be herbivore (eating a whole seed)

Grazing (herbivory) –

one organism consumes small parts of another organism

(prey don’t die quickly/at all, many prey attacked)

Parasitism –

one organism consumes small parts of / steals resources of, another organism that it lives in close association with

(prey don’t die quickly/at all, very few prey attacked)

Stable predator-prey cycle:

A dynamic where predator and prey populations oscillate over time with delayed responses (e.g., as prey increases, predator increases after a lag).

Mite predation experiments:

with no refuges: both died

refuges help stabilize predator-prey dynamics, preventing extinction.

Mutualism

when two interacting individuals both experience a net benefit from an interaction (+/+)

common in harsh env wheres species struggle to persist

By-products benefits - benefits of mutualism outweigh costs of

mutualism for both species

Can involve protection from predators/herbivores/ competitors,

or increased access to resources

tightly linked mutualism can lead tp

co-evolution

E.g., Hummingbird bills have co-evolved with flower shape

Symbioses

close, prolonged interaction between two species,

often with one species providing habitat for other species to live in.

Obligate mutualism

a mutualism in which at least one of the interacting

organisms cannot survive without the other organism

Buchnera can no longer live on their own – they require host

environment to survive

Commensalism

when one individual benefits from an interaction

and the other species neither benefits nor is harmed (+/0)

Facilitation

when one species benefits another species indirectly, often through its impact on a third species or on the environment itself