How Changes Occur Naturally in Ecosystems

The Stickleback: Adapt or Die

Occupied oceans of the northern hemisphere Trapped in lakes as the glaciers retreated Adapted to freshwater environment, forming

a new species of sticklebacksIn BC pairs of sticklebacks developed

Lake bottom: feed on snails and clams – chunky bodies with wide mouths – little armour and fewer spines than ancestors

Open water: slender bodies and narrow mouths – retained more spines and armoured side plates – lighter in colour

How Organisms Adapt to Change

Living organisms changes as the abiotic and biotic elements of an ecosystem change

Natural Selection: members of a species having certain characteristics that give them an advantage will be in better condition to mate Will pass on favourable characteristics to

offspring

Example: the Galapagos finchesScientists believe that 13 species developed

from a single species from South America

Adaptive Radiation: the change from a common ancestor into a number of different species that “radiate out” to inhabit different niches Examples: Sticklebacks and Cichlid (more than 300

species from a single ancestor)

Galapagos finches: each species adapted to the ground or in trees; each gathers and eat different food; evolved different size beaks and shapes depending on food source

How Ecosystems Change Over Time

Ecological Succession: changes that take place over time in the types of organisms that live in an area

There are 2 types of ecological succession: 1. Primary Succession 2. Secondary Succession

1. Primary Succession

Occurs in an area where no soil exists (bare rock)

Natural events (ex. retreating glaciers) can scrape rock bare, or new rock could form after a volcanic eruption

Wind and rain carry spores of organisms, like lichens, to these areas

Lichens... An organism consisting of a fungus and an alga Obtain nutrients from rocks by secreting chemicals

that break down the rock

Weathering by lichens, wind, rain, and freezing begin soil formation

Dead lichens provide additional organic matter to developing soil

RESULT: Soil accumulates (even though it could take hundreds of years

Spores from plants, like mosses, will be deposited by the wind and start to grow Most have adapted to grow in harsh/nutrient poor conditions

Pioneer Species: lichens and plants that are the 1st organisms to survive and reproduce in an area

Pioneer species change the biotic and abiotic environment in many ways... Decay and create more soil Make soil more fertile and increase ability to hold moisture Provide food for insects and other organisms, introducing

animals to the community

Each stage of primary succession is gradual and introduces different populations of micro-organisms, plants and animals that will compete for nutrient, moisture, and sunlight

As these organisms decompose, they contribute more organic matter to the soil layerEventually, seeds of trees will germinate

1st trees usually requires lots of light (ex. deciduous trees of boreal forests)

The shade will change abiotic conditions as soil becomes cooler and more moist Only shade tolerant plants will grow

As more niches are created, there is be greater diversity in organisms creating more complex food webs

Primary succession occurs in the same way globally Coniferous forests in northern latitudes Deciduous forests in temperate zones Tropical forests in tropical zones

See Figure 3.8 on page 112-113 for a detailed breakdown!

2. Mature CommunitiesClimax Community: a mature community

that is the result of primary succession Includes boreal forests, tropical rainforests,

grasslands, and desertsEven though a climax community may appear

unchanged, there was always changes occurring because of small disturbances Alder may grow because a tree has fallen, allowing

more sunlight throughScientists now prefer “mature community”,

reflecting the idea that it is always changing

3. Secondary Succession

Occurs as a result of a disturbance to an area that already has soil and was once the home of living organisms

Occurs much faster than primary succession because soil and nutrients already exist Primary might takes 100’s of years, secondary could

only take decades Often depends on the recovery of existing

plants, such as trees, and on species that can rapidly reproduce in new conditions of increased sunlight and open areas

How Natural Events Affect Ecosystems

1. FLOODING Occurs in coastal areas, rivers, and lakes

when the volume of water exceeds the ability of the water body to contain it

Can be part of a normal cycle or caused by heavy rainfall, increased run-off, melting snow, or an extreme natural event (tsunami)

Can result in soil erosion and soil pollution (if chemicals are present)

Can cause widespread disease if untreated sewage enters drinking water supplies Climate change could cause an increase in flooding due to heavier rains

2. TSUNAMISA huge, rapidly moving ocean wave Usually caused by large earthquakes or

underwater volcano eruptionsOn land, the wave carries away or destroys

plants and animals (affecting food webs) Salt water changes composition of soil

plants that can’t survive salty environment won’t grow

3. DROUGHTUsually occurs when there is a below-average

amount of precipitation over a period of many months or years

Ecosystems usually recover when regular precipitation pattern re-establish

destroys habitats when water is scarce and animals die Can result in crop failure and livestock deaths

Made worse by climate change Experienced by Australia, western Europe, and Africa

4. INSECT INFESTATIONSHave an important role in natural succession

of forests Mountain pine beetle destroys older trees nutrients

get recycled Younger trees usually able to resist by producing resin

If many insects attack or if tree is stressed (overcrowding, drought, grazing) it won’t produce as much resin Beetle carries a fungus which than destroys plant

tissues and prevent resin production

Cold winters, which kill beetle larvae, are affected by global warming

Suppression of forest fires has resulted in a large number of host trees

Because beetle population isn’t in check, other species are losing their homes