topic 17 - symbiosis

Symbiosis

Interactions where two or more species live purposefully in direct contact with each other.

Commensalism

Help | No Effect

One benefits, other neither benefits or harmed

(Eg. Elephant walks past, kicking up insects, which is then eaten by birds)

Community effects

• Interactions that later survival of individuals can affect population growth

• Mutualism and commensalism can therefore shape population and community dynamics

Stress-gradient hypothesis predict

• Competition (antagonistic) relationships more common in lower stress environments

• Mutualism (facilitation) more common in higher stress environments

Community effects

• Interactions that later survival of individuals can affect population growth

• Mutualism and commensalism can therefore shape population and community dynamics

Stress-gradient hypothesis predict

The stress-gradient hypothesis (SGH) is an ecological concept that predicts how the balance between competition and facilitation/mutualism changes along environemtnal stress gradients.

Environmental stress (eg droughts, salinity, temperature extremes, nutrient limitation) affects how species interact

Predicts that:

• In low stress environments (favourable conditions): competition dominates because resources are abundant and species compete for the best spots or resources.

• In high stress environments (harsh conditions): facilitation or mutualism dominates because species help each other survive the stress eg. Providing shade, nutrients, or structural support

• Competition (antagonistic) relationships more common in lower stress environments

• Mutualism (facilitation) more common in higher stress environments

Mutualism (symbiosis)

Help | Help

Both species benefit from

(Eg. Frogs each ants that prey on spider’s effs, large spider provides frogs protection from larger predators like snakes)

Parasitism

Help | Harm

One species benefits, while the other is harmed

(Eg. Tick feeding on blood of lioness)

• Smaller than their host

• Live on or in the host for extended period of time

• Usually don’t kill the host (but can)

• Hosts can recover from parasites

• The habitats of parasites are themselves alive, and they can: grow, mount defences against parasites, evolve, move

• Often live in highly specific sites (eg, gut, bloodstream, skin)

• Challenge: crowding and competition with other parasites or microbes for space and nutrients

• Rely on host for nutrition, reproduction, or dispersal

• Host defence

Parasites can be:

• Protozoans

• Animals

• Fungi

• Plants

Microparasite

• Small and often intra-cellular

• Multiply directly within their host

• Often extremely numerous

• Eg. Viruses, bacteria, Protozoa

Macroparasite

• Grow on or in host but do not multiply in their host

• Produce infectious stages which they release into the environment to find new hosts

• Often live on the body or in the body cavities (eg. Gut, intestines) rather than being intracellular

• Eg. Helminths, nematodes, tapeworms

Kleptoparasitism

One organism steals resources (usually food or prey) that another organism has caught, collected, or prepared.

Parasite benefits by saving time and energy, while the “host” loses resources (eg spiders live on another spider’s web and steal prey)

Monoxenic life cycle

Direct life cycle - life cycles that features just one host —the parasite completes its entire life cycle in a single host species - transmission is usually from one host individual to another (eg through faeces, contaminated food/water or direct contact)

Heteroxenic life cycle

Indirect life cycle - involve multiple (often completely unrelated) organisms as hosts — one is often a definitive host (where sexual reproduction occurs) - others are intermediate hosts (where development or asexual reproduction occurs)

Symbiosis based on dependency

• Obligate symbiosis

• Facultative symbiosis

Obligate symbiosis / mutualism

Species that rely on the other, cannot survive without the other

Eg. Termites and gut protists

Facultative symbiosis / mutualism

Survive individually when separated, just not well

Eg. Clownfish and anemones

Symbiosis based on level of specialisation

• Specific / highly specialised

• Diffuse

Specific / highly specialised

Close and exclusive relationship, with just one other species (eg leaf cutter ants and fungal as food source)

Diffuse

Includes multiple species

Symbiosis based on physical association

• Endosymbionts

• Ectosymbionts

• Endoparasites

• Ectoparasites

Endosymbionts

Inside the body or cell of the organism, dinoflagellants inside corals (eg. Mitochondria, gut bacteria)

Ectosymbionts

Organism lives on body surface of organism

Eg. Cleaner fish hold onto sharks

Endoparasites

Internal parasites

Eg. tapeworm

Ectoparasites

External parasites

Eg. Ticks, lice

Symbiosis based on nutritional mode

• Autotroph

• Heterotroph

• Parasite

Autotroph

Synthesise own food through photosynthesis

Heterotroph

Rely on other organisms for nourishment

Parasite

Lives off a host organism, causing the host harm or death

Symbiosis in plants

• Autotrophic plants

• Epiphytes

Epiphytes

Plants that grow n other plants for physical support (host plant often has them higher up) specialised roots that anchor them to the host