21 - Interspecific competition and mutualisms

Mechanisms of reciprocal negative interactions
between species,

Exploitation competition (competing for same resource

Interference competition (preventing access

Intraguild predation (eat each other)

Apparent competition (common predator)

Lotka-Volterra competition equation

where alpha is competition cofficient I.e effect of species 1 on 2 and vice versa

Competition

interaction between species in which they vie for the same limited resoures (food, watewr, territory)

Competitive exclusion principle

two species cannot coexist indefinitely on the same limiting resource (one species will win)

How do species evolve to avoid similarity?

• Resource partitioning (niche partitioning)
• Character displacement
• Niche expansion

Keystone species

• Speices that habve a major effect on overall communityu structure (greater than would be expected based on their abundance or biomass

• Can influence competition

Darwin’s Finches - character displacement

different finches occupied different beak size niches

as more species were introduce, the extremes become less varried and narrows.

Symbosis and Mutualism

Symbiosis: species living in close and long-term association. Not necessarily mutualistic

MUtualismL associaiton is benificial for both partners. Not necessarily symbiotic

Mutualisitic-Symbiotic vs not symbiotic examples

symb - Human gut microbiota
non symb - Plants and mycorrhizal

Commensal - Symbiotic vs non symbiotic

sym - Lichens growing on tree
bark

non - All kinds of interactions

Harmful - Symbiotic vs non symbiotic

sym - Pathogenic microbial
infections

non - Predators, etc.

Examples of mutualism

pollination, fruit dispersal, cleaning (parasite removal), defensive association (ants protect plants)

Parasitism-mutualism continum (fleeting paractism and mutualism examples)

Paracitism - Seed-eating birds, cleaner cheaters, pollinator cheaters

Mutualism - Fruit-eating birds, cleaner fish, plants and pollinators

Parasitism-mutualism continum (long lasting (<1 gen) paractism and mutualism examples)

Parasitism - Many parasites

Mututalism - Mycorrihizae, Ants * acacias

Parasitism-mutualism continum (Many gen paractism, comen and mutualism examples)

Parasitism - Plant Viruses, Wolbachia

Commensalism - Wolbachia

Mutualism - Wolbachia, Buchnera, organelles, Endophytic fungi, Leaf cutter and N2 fixing fungi

Symbiotic mutualism as mechanism of evolutionary innovation and adaptive radiation examples

For one to exist, the symbiotic mutualism must have been selected for and filled an open niche.

Euk cells - Mitocondria

Photosynthesis - chloroplasts

Colonization of land by plants - mycorrhizae

Nitrogen fixation by plants (rhizobia)

Deep-sea vent animals - chemoautotrophic life systems

Partner-fidelity feedback (symbionts)

Short term <1 generation

A directly benefits B, who later provides a benefit to A. Positive feedback cycle

-metabolic complementarity

-provide defense against natural enemies

co-transmission (symbionts)

Long term >1 generation

correlation in fitness between genetic elements causes this

• increase in fitness of host leads to increased fitness of maternally transmitted symbiont (ex. mitocondria)

Symbiosis important variables

• route of infection (vertical, horizontal mixture)

• Effects on hosts (paracitism-mutualism, effects on fitness)

• Duration of the association (<1 gen to millions)

• Mechanisms

Mechanisms of Symbiosis

– Location of symbionts in host body: intracellular, between cells, in
specialized organ or in other tissues, within gut lumen, external
– How cells are invaded (e.g., secretion systems)
– How symbiont affects host fitness

Routes of transmission (3)

Vertical (parent to offspring); usually through the egg,
seeds

Typically, from the mother only

Horizontal
- From the outside environment

- Example: squid and Vibrio bacteria (bioluminescent)

A mixture of vertical and horizontal
– Acquire from mother, other individuals, or external
environment
– Example: gut flora of termites

Spread of vertically transmitted microbes

• Increased host survival and reproduction

  • Metabolic benefit → mitochondria and chloroplasts

• Reproductive manipulation (paracitism

  • Feminization, male killing, Cytoplasmic incompatibility

Only way for purely parasitic types to spread

Mixture of vertical and horizontal transmission.