G.3 Impact of Humans on Ecosystems

# G.3 Impact of Humans on Ecosystems

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## G.3 Impact of Humans on Ecosystems

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1. G.3 Impact of Humans on Ecosystems

2. Biological Diversity of Species Richness and Evenness

3. Richness • Richness – The number of species per sample is a measure of richness. The more species present in a sample, the 'richer' the sample. • Species richness as a measure on its own takes no account of the number of individuals of each species present. Thus, one daisy has as much influence on the richness of an area as 1000

4. Evenness • Evenness is a measure of the relative abundance of the different species making up the richness of an area.

5. Example: We sampled two different fields for wildflowers. • The sample from the first field consists of 300 daisies, 335 dandelions and 365 buttercups. • The sample from the  second field comprises 20 daisies, 49 dandelions and 931 buttercups • Both samples have the same richness (3 species) and the same total number of individuals (1000). • The first sample has more evenness than the second. This is because the total number of individuals in the sample is quite evenly distributed between the three species. • Sample 2 is considered to be less diverse than sample 1.

6. See other example in book page 572

7. Simpson Diversity Index • A measure that takes into account both richness and evenness. The formula: D = N(N-1) • Sn(n-1)

8. D = diversity index • N = total number of organisms in the ecosystem • n = number of organisms of each species • When comparing two ecosystems, the one with the higher diversity index is more diverse • See problem on page 573 - 574

9. Conserving biodiversity • Economic • Ecological • Ethical • Aesthetic

10. Invasive (alien) species • Outcompete native species – Red squirrel/grey squirrel. May result in extinction – Nile perch • May prey on native species - lamprey • Can take advantage of disturbed areas and thrive without competition

12. Biological control • Involves introducing a natural predator to control unwanted or invasive species

13. Cane Toads • Cane toads are large, robust amphibians which are native to Central and South America. They are extremely hardy animals and voracious predators of insects and other small prey. They were introduced to Australia as a means of controlling pest beetles in the sugar cane industry in 1935, before the use of agricultural chemicals became widespread.

14. The Mongoose: A Maui Menace • Was introduced to rid the cane fields of rats • Unlike the nocturnal rats, the mongoose is active during the day. So instead of ridding the islands of rats, the mongooses have found many other things to eat instead. There are few things a mongoose WON’T eat! • Many of Hawaii's birds nest on the ground and the mongoose eat their eggs

15. Cute Killer!!!!

16. Biomagnification • As you go up each trophic level, chemical toxins may become concentrated in the bodies of higher consumers. • These chemicals are stored in the fatty tissues of the consumer. • DDT is an example biomagnification. On the gulf coast it was used for mosquito control where it entered the water supply.

17. UV Radiation • The ozone layer protects the earth from ultraviolet radiation. • Consists of a layer of O3 about 20 km thick, 15-35 km above the earths atmosphere

18. Thinning of ozone • Chlorofluorocarbons (CFC’s) are the cause. • CFC molecules break down and release Chloride ions. Recall that the halogens are highly electronegative. These break down and react with ozone for form ClO and O2. • ClO then reacts with an oxygen atom forming more O2 and a Cl-1. • This free chloride continues to destroy ozone molecules for up to 100 years! 

19. CFC’s are found in • Aerosol propellants • Refrigerator and AC coolants • Material used to make foam packaging • These have been being phased out since the Montreal Protocol signed in 1987 and substantially amended in 1990 and 1992.

20. The Montreal Protocol stipulates that the production and consumption of compounds that deplete ozone in the stratosphere--chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform--are to be phased out by 2000 (2005 for methyl chloroform). • Has this happened?????

21. Effects of UV radiation • DNA mutation • Sunburn • Cataracts – clouding of lens of eye • Reduced biological productivity • Damages and kills plant cells. Less photosynthesis. Phytoplankton are especially at risk. • Skin cancer • Nonlethal – basal and squamous cell carcinoma • Lethal – malignant melanoma (lethal in 15 – 20 % of cases)