Interactions in the Ecosystem

Biology 250

Species Interactions• Symbiosis – A close interaction between two

species• There are 5 types of symbiosis– Predation – when one individual, the predator,

captures, kills and consumes the other individual, the prey• How do you think predator-prey relationships can

influence evolution by natural selection?

The 5 types of symbiosis continued• Defense against predators:

– Mimicry – when a harmless or good-tasting species resembles a harmful or bad-tasting species. Also, when two or more dangerous species resemble each other.

– Warning coloration. Advertising you’re bad news.– Plant-Herbivore interactions count as predator-prey

interactions and plants produce secondary compounds to protect themselves (chemicals which are poisonous and irritating). What other ways do plants protect themselves?

– Parasitism – One individual, the host, is harmed while the other individual, the parasite benefits.• Usually does not kill the host.• Ectoparasites – live on the outside of the body• Endoparasites – live on the inside of the body

5types of symbiosis continued– Competition – Results from fundamental niche

overlap.• Usually, one organism will be able to use a resource

more efficiently.• Competitive Exclusion – when one species is eliminated

from an area due to being outcompeted for a resource.– Is this more likely to happen to a generalist or a specialist?

• Resource Partitioning – When organisms utilize different parts of the same resource

5 types of symbiosis continued– Mutualism – when both species involved benefit

from the interaction• Pollinators are great examples of mutualism. The bees

get food and the flowers get pollinated.• Ants and the acacia tree. The hollow thorns give the

ants a home and the ants protect the tree from herbivores.

– Commensalism – When one organism benefits and the other is neither harmed nor helped• Cattle egrets and cape buffalo. The movement of the

buffalo drives small organisms out of their burrows and the egrets swoop in and eat them.

Review!

• Ok… what are the 5 types of symbiosis again??

Predation

Parasitism

Competition

Mutualism

Commensalism

Energy Transfer in the Ecosystem• Food Chains – Feeding relationships– All food chains start with

energy from the sun– First level of all food chains

are producers – organisms which make their own food.

– Most food chains only go up 4 or 5 levels

– All levels connect to decomposers.

Sun

DecomposersBacteria

Fungi

Level 1

Level 2

Level 3

Level 4

Energy transfer continued.

17%growth

33%cellularrespiration 50%

waste (feces)

energy lost todaily livingenergy lost todaily livingonly this energy

moves on to the next level in the food chain

Even though 17% of energy goes to growth only 10% of the energy moves on to the next trophic level as we don’t eat all parts of an organism.

Energy transfer continued.• Feeding levels – how much

energy can you get?– You can only get the energy

stored in the organism– Producers take energy from

the sun and create sugars.– Consumers eat other

organisms for their food.– Food chains can only have 4

or 5 levels.

Energy transfer continued• Food Webs – shows a

more complete picture of the interaction between species.– There are many

connections throughout the system.

– Formed from interconnected food chains.

Energy transfer continued.

Energy flows through an ecosystem.

Nutrients are recycled.

Energy transfer continuedThere is a loss of energy between each level in a food chain. The amount of energy available at each level can feed fewer and fewer individuals.

This is why food chains are short!

Energy transfer continued

How does this relate to the

ecology issue of the exploding

human population?

Energy transfer continued• Remember, energy flows through an

ecosystem but nutrients are RECYCLED.– Decomposers work on organisms of all trophic

levels to break down their bodies and return the nutrients to the ecosystem.

– Without decomposers, all the nutrients on Earth would be trapped in dead bodies!

Bioaccumulation• Bioaccumulation- increase in concentration of

a substance(s) in an organism • Why do the toxins build up?• Toxic substances are lipophilic or fat-loving,

(fat-long term storage) The toxic substances are very slowly metabolized or excreted so if the organism keeps on consuming prey or food contaminated with toxic substances, the concentration of the substance will further increase in its body

Biological Magnification• Because the number of organisms at each

trophic level is smaller and smaller, toxins introduced in the first trophic level will become more concentrated at each trophic level.– If one blade of grass has just one particle of a toxic

substance then…• An insect which feeds on grass may consume 50 blades of

grass in its lifetime. So each insect would have 50 particles of toxin.

• An organism who feeds on insects might consume 50 insects in its lifetime and would then contain 2500 particles of toxin.