Ecosystems and living organisms

Chapter 5

Evolution: populations change

• Evolution: genetic change over time• Charles Darwin: traits favorable to survival would

be preserved; frequency of favorable traits increase in subsequent generations

• Adaptation: evolutionary modification that improves survival and reproductive success

• Natural selection based on observations: overproduction, variation, limits on population growth, differential reproductive success

Natural Selection

• Darwin’s finches exemplified the variation associated with natural selection

• Bottleneck – reduced genetic variation due to reduced population size. Ex: hunting of Elephant seals.

• Founder effect – when only a few organisms colonize an area. Reduced genetic variation; non-random of original gene pool

Check for understanding• 4 - I can explain evolution and natural selection to

my peers• 3 - I understand how variation leads to varying

levels of survival and over time this leads to evolution.

• 2 - I understand that evolution is genetic change over time, but I don’t really get how it happens.

• 1 - I am lost about natural selection and evolution

Succession: how communities change over time

• Species in one stage being replaced over time by others; a constant process; no real climax community– Primary succession – occurs where no organisms have

been before; no soil• Ex: created by volcanic lava, rock revealed by retreating

glacier• Pioneer community: initial growth, typically lichens which

secrete acid that breaks rock to start forming soil. – Then mosses and ferns grasses and herbs low shrubs

trees.– Secondary succession – change in species composition

after a disturbance has destroyed the existing vegetation; soil is already there.• Ex: after a fire, abandoned farmland

Secondary Succession of Secondary Succession of an abandoned farm field in an abandoned farm field in North CarolinaNorth Carolina

Check for understanding• 4 - I can explain succession (both primary and

secondary) to my peers• 3 - I understand the difference between

primary and secondary succession.• 2 - I understand primary and secondary

succession but can’t give examples• 1 - I am lost about succession

INTERACTIONS BETWEEN ORGANISMS

Keystone species• A species that is more important than expected based on

amount to the stability of the ecosystem than others. – Ex 1: gray wolf – their decline increased herbivore numbers when

then overgrazed. Insects declined because their food (plants) were declining.

– Ex 2: fig trees in tropical rain forest – animals eat figs when other fruits are not abundant

– Ex 3: starfish (Pisaster ochracceus) – predator, two mussle species grow unchecked without them

• Conservation efforts focus on protecting keystone species – easier to protect just one to balance an entire community.

1. Symbiosis: intimate relationship between at least 2 species

• A result of coevolution– Ex: plants and pollinators. Plants have nectar,

pollen, color, scent. Pollinators have hairy bodies, shape of beak

• Types: mutualism, commensalism, parasitism

• Mutualism – benefits are shared– Ex: nitrogen –fixing bacteria (Rhizobium) and

legumes (peas/beans); plants get nitrogen and bacteria get food source.

– Ex: zooxanthellae (microscopic algae) live inside coral cells and perform photosynthesis. – Coral gets nutrients (nitrogen, carbon, oxygen) &

calcium carbonate skeletons form around bodies faster with algae. – Algae get shelter and nutrients (ammonia waste from

coral and carbon dioxide)

Mutualism• Ex: Mycorrhizae fungi and plant roots– Fungus provides better absorption of water and

minerals (like phosphorus)– Roots provide fungi with food (sugar) produced by

photosynthesis in the plant

Left: root growth Left: root growth without fungiwithout fungi

Right: root growth Right: root growth with fungiwith fungi

• Commensalism – taking without harming– Ex: epiphytes on trees. Epiphytes gain location for

light, water, nutrients but doesn’t affect tree

• Parasitism – taking at another’s expense– Rarely kills host– A factor in the decline of honeybees (in addition

to pesticides and habitat fragmentation)– Disease/death causing = pathogen

Parasitic mites in bee’s trachea

Other interactions

2. Predation– Result’s in “arms race”; genetic changes to help capture

prey or avoid predator– Adaptations: • Pursuit – better hunting efficiency (like speed) larger

brains than prey• Ambush – camouflage or attracting prey (anglerfish)• Plant defenses – thorns, waxy leaves, toxins (nicotine,

opium poppy)• Animal defenses – shell, speed, herds, chemicals,

camouflage

3. competition: more than one individual try to use the same resource– Intraspecific competition: within population– Interspecific competition: between species

Check for understanding• 4 - I can explain at least 4 different ways

organisms interact to my peers• 3 - I understand many different ways

organisms interact and can give examples of each.

• 2 - I understand different interactions between organisms but can’t give examples

• 1 - I am lost about how organisms interact.

Ecological niche• The role an organism plays in ecosystem• Includes habitat, what it eats, what eats it,

what organisms it competes with, other community interactions, how it is affected by abiotic factors (light, water, temperature)

niche

• Fundamental niche – potential/idealized• Realized niche – actual niche(less due to

competition)

Factors determining niche

• Limiting factor: any resource –scarce/unfavorable – restricts ecological niche.

• Competitive exclusion – due to competition, one species is excluded from a portion of the niche. (interspecific competition)– Ex: brown/green anole– Ex: paramecium – P. aurelia and P. caudatum

(larger)• Resource partitioning – avoid/reduce resource

competition; favored by natural selection; no two species have exact same niche

Interspecific Competition

Check for understanding• 4 - I can explain to the class the relationship

between interspecific competition, competitive exclusion, and resource partitioning.

• 3 - I understand interspecific competition, competitive exclusion, and resource partitioning.

• 2 - I understand the definitions, but need some more practice.

• 1 - I am lost about interspecific competition, competitive exclusion, and resource partitioning

Species richness

• # of species in community; increases community stability; affected by:– Abundance of niches– Ecotone: zone between communities, increased species

richness due to increased quantity of niches (edge effect)– Geographical isolation – decreases richness (smaller area

decreases available niches); ex: islands, mountaintops; the more isolated and smaller in size decreases richness.

– Dominance of one species reduces richness: takes resources/outcompetes other species

– Environmental stress of habitat reduces richness (polluted stream)

Ecosystem services

• what ecosystems do for other organisms, including humans

• Greater species richness = better ecosystem services

• Ex: provide habitat, forests provide wood, purify air/water and absorb CO2, grasslands provide humans with livestock, rivers provide recreation and methods of transportation

Check for understanding• 4 - I can explain to the class how ecosystem

services are related to species richness.• 3 - I understand factors that influence species

richness and can define ecosystem services.• 2 - I either understand only species richness

or ecosystem services, but not both fully.• 1 - I am lost about ecosystem services and

species richness