17.3 - Mutualism and Commensalism

mutualism

both species benefit from interaction

mutualism example

1. hermit crab moving anemone on shell - anemone provides protection and crab provides scrap food

2. pistol shrimp dig holes into sea floor providing homes for gobies and as the shrimp are basically blind gobies alert them to potential predators

pollination

type of mutualism btwn flowering plant and animal pollinator - process of transferring pollen from an anther to a stigma

• plant benefit = animal moves pollen between plants fertilising flowers

• pollinator benefit = pollen or nectar for food

facultative pollination

flowering plant and pollinator survive without the interaction

• good - wide variety of pollinators are available = if 1 species declines/extinct other pollinators will be available

• bad = not always guaranteed pollen will be transferred to other members of same species

obligate pollination

flowering plant and its specific pollinator are mutually dependent for survival

• good - higher chance of pollinators visiting same species

• bad if pollinator goes extinct as puts plant at risk of extinction

how do plants deal with the adv/dis of obligate and facultative pollination

evolving adaptions that encourage repeat visits by pollinators whilst discouraging others e.g. nicotine in tobacco plants - insects become addicted while hummingbirds don’t receive enough to = repeated visits by specific pollinators

why is balance needed for plants concerning plant dispersal via animals

discourage eating before seeds are ready and attracting when dispersal is needed.

is lichen an example of mutualism and if yes which type?

Yes - obligate mutualism - composed of a fungal and an algal/cyanobacteria partner

• algal/cyano provides food via photosynthesis

• fungal provides protection from enviro variability

mutualism between coral and zooxanthellae

• endosymbiotic zooxanthellae provide nutrients through photosynthesis

• corals offer shelter, access to sun and produces ammonium which zoo use as source of nitrogen

this relationship allows coral to survive in nutrient poor waters bc recycles nutrients

coral bleaching 

when corals lose their zooxanthellae due to increasing temps, leading to a decrease in color and a loss of essential nutrients, making them more vulnerable to stress and mortality.

commensalism

one species benefits while the other is neither helped nor harmed.

commensalism examples

1. specialised - cattle egrets associate with cows as they dislodge insects from ground when grazing = food for egrets

2. general - bird living in tree = bird has a safe space and tree not affected

deceptive pollination

a strategy used by some plants where they mimic cues to attract pollinators without providing rewards, ensuring their own reproduction

example of deceptive pollination

Hammer orchid - mimics the appearance and scent of a female wasp = male attempts to mate with flower picking up/depositing pollen. Orchid doesn’t provide any reward so wasp tricked into pollination

stress-gradient hypothesis

nature of interactions between species shift along gradient of environmental stress

• competition (antagonistic) dominates less stressful conditions bc resources are abundant

• mutualism (facilitation) more in higher stress environments bc assist each other for survival

co-evolution

process where two or more species influence each other's evolutionary pathways thru reciprocal adaptations

co-evolution under parasitism

arms race where parasites and their hosts adapt in response to each other's changes bc parasite wants to keep its benefits and host wants to prevent harm

co-evolution under mutualism

both species adapt to increase mutual benefits

How could positive interactions affect population growth and community structure?

• increase growth by improving survival, reproduction or resource access

• enhance co-existence by reducing competition or stress

• create positive feedback loops that influence species abundance and spatial distribution