3 1 How Changes Occur Naturally in Ecosystems

3. 1 How Changes Occur Naturally in Ecosystems 1. ORGANISMS CHANGE • An organism belongs to a species, but is also born with unique characteristics. w E. g. , humans have different eye colours and heights • Sometimes the unique characteristics give the individual an advantage. w E. g. , a salmon with a slightly larger tail may be able to swim a little faster or farther in a river. • Natural selection is the process wherein advantageous characteristics grow more common in a population, because individuals with that characteristic are more likely to survive and reproduce. E. g. , the larger-tailed salmon will survive better and spawn better, and the offspring have more chance of See pages 108 - 109

• Birds on the Galapagos Islands, off the coast of Ecuador, appear to be products of natural selection. w There are thirteen species of finch on the islands, and they are Galapagos very similar finches w It is believed that all species started as a single species that was changed by natural selection – finches in one area changed in one way, finches in another area changed in another way, etc. w Each species has unique characteristics that allow it to them thrive in its own niche, and not compete with other species for resources. • Adaptive radiation is when many species, inhabiting different niches, are thought to have developed from one common ancestor. See page 110

2. • ECOSYSTEMS CHANGE Ecological succession = the changes in biotic characteristics in an area over time. w Two types of ecological succession: primary succession and secondary succession • Primary succession - begins with nothing but bare rock STAGES: 1. Bare rock § E. g. , glacier scrapes away surface layer § E. g. , lava from volcano cools 2. Lichens (a fungus & algae combined) § Do not need soil; secrete chemicals that break rock down § Spores carried to the area by wind & rain pages 111 - 113 § Pioneer species = the first organisms to live in an. See area

3. Soil formation begins § from lichen breaking down rock § from dead lichens decomposing § from natural weathering processes breaking down rock (wind, rain, landslides) § Soil may take hundreds of years to accumulate 4. Mosses § Can grow in little soil and nutrient-poor environments § Add more nutrients to the soil when they die and decay 5. Small plants § There is enough soil built up § Grasses, wildflowers & shrubs § Greater variety of insects, micro-organisms and small animals § Add more organic matter so soil layer increases See pages 111 - 113

6. Sun-tolerant trees § e. g. , deciduous trees § seeds brought by wind, water or animals § greater diversity of species, including larger animals § trees produce shade under them, which produces new abiotic conditions • cooler temperatures • moister soil 7. Shade-tolerant species § E. g. , coniferous trees § Eventually they grow taller than the other trees and take over § A mature forest has developed • will remain largely the same over time (only slow or small changes) • Called a climax community w Primary succession occurs similarly in all parts of the world.

• Secondary succession – occurs after a major disturbance in an area that already has soil and once had living organisms. w forest fires are the most common reason w The soil remains… § providing for plant growth § containing seeds, micro-organisms, earthworms and insects w much more rapid than primary succession w only lasts decades See page 114

• Natural events affect ecosystems 1. Forest Fires § Already discussed 2. Flooding § Can be caused by: • Heavy rainfall • Increased run-off from snowmelt • Tsunamis • Natural cycles § Possible effects on ecosystem: • soil erosion • soil pollution (if toxins in water) • spread of disease (if harmful bacteria in water)

• Natural events affect ecosystems 3. Tsunamis = a huge, rapidly moving ocean wave § Usually caused by large earthquakes or underwater volcanic eruptions § Effect on ecosystems: • Destruction of plants & animals • Large volume of salt added to soil 4. Drought = when an area receives a lower than average amount of rainfall over a long period of time § Effect on ecosystems • plants & animals die § Often, ecosystem can recover when it rains again See pages 115 - 116

• Natural events affect ecosystems 5. Insect Infestations § Many insects play important roles in their ecosystems § Even insects that appear destructive, such as the mountain pine beetle, actually play a role in the renewal of the forest § When normal conditions are changed, insect infestations can occur. • E. g. , a warmer climate in BC not cold enough to kill the beetle larvae • E. g. , suppression of forest fires beetles able to spread more effectively § Negative effects of pine beetle on BC forest ecosystem: • Pine tree populations devastated • Bird and mammal nests lost • Human forest industry