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Lecture

BGYC63 Oct18


Department
Biological Sciences
Course Code
BIOC63H3
Professor
Ivana Stehlik

Page:
of 5
Oct18 BIOC63
Threats to Biodiversity
- impacts of global change on biodiversity
- the effects of fast change on biodiversity
Global Change
- most peopel think of climate change when we hear "global change"...this is mostlikely to effect the
Arctic area
- Nitrogen deposition is the least known, however, it is changing the most strongly in our types of
ecosystems
A. Eutrophication (N deposition)
- why focus on this?
- N, P, K are typically most limiting nutrients (important in fertilizers) it is one of the most
limiting resources for plants...and N has the largest human impact
- where is N located?
- in the atmosphere (N2): atmospheric composition -> 78%(N2), 21%(O2) 0.04%(CO2)
- however, this N2 in the atmosphere is very unreactive...so not very useful for
living organisms
- 3 types of reactive N: 1) Organic( from plant and animal tissue)
2) NH
3)
1. Nitrogen Cycle
- the pool it comes from is from the atmosphere
- the lightening has enough heat and pressure turns atmospheric N into
bioaccessbile N
- another (more) imporant was is N fixation by bacteria, once the bacteria die, they
decompose in the soil and they turn into animo acids, and they are decomposed by
other bacteria into ammonia, then nitrite then finally nitrate
- another important bateria (not free living, but living on the roots of plants) are
rhzibia, they use the nitrogen for themselves, but the left over, they transfers into
plants which are then decomposed like the above, or if the plants are consumed by
animals, through uric acid and urea turns into ammonia and so on
- the nitrogen in the soil can also be be absorbed by other plants
- and the access nitrate in soil will be absorved in the atmosphere
- N is so limited that any N abailable is taken by plants as soon as it was created
- before we tinguered with N, it pretty much stayed within the community, as soon
as something died, it was quickly taken up by another living organism, it was s
closed system!
- before we started using fossel fuel, we had access through the activiety of
bacterias
2. Human influence on the N cycle
- very expensive reaction...fueled by fossil fuels; but through this we now have
access to N
- from this we have changed the global nirogen cycle
- background fixation rate is about 110Tg per year
- by us, we have more than doubled the numbers by the Haber-Bosch process, the
plants that we choose to plant, and by burning fossil fuels
- if there is extra N in soils, the N returns to the atmosphere, but still as an bioactive
N; which rains down on the soil again and fertilizes area
- each year, ever square metre gets about 2 pennies worth (weight) of N
3. Excess N in terrestrial systems
- plants have thier potimum of which it grows best in terms of fertilizer
- under unproductive, low N communites (N limited communities), plant
communities will generally be more diverse
- high nitrogen conditions, only a few species can make good use of it,
those that can do this will grow vigerousely and outcompete others
- the less competitive species will lose out
- if everything is limited, all plants are "stunted" giving more space for other
species to come in
- in very low nitrogen conditions evoluition of high diversity; some will even
become cornivores and eat insencts for N
- reaction to N load on 3 plant species
- Drosera Rotundifolia lives in areas of low N (they eat insencts)
- they are not very effected with low N, but when N is added, thier
numbers decrease
- theyare croweded out by other species then N increases
- Neschampsia flexuosa, with high addition of N, it crowded out every one
else
- Brachypodium..., by increasing N, same effect as above
- therefore, change in competitive conditions of plants
- the above 3 was a lab experiment, but we also see this in real live
- the graph shows that the lower N is deposited, and diversity has a correlation, the
less N, higher diversity
- the effects of N on plants, very little had direct effect to N (so N was directly toxic)
but most had effects through soil acidification, and in all terrestrial systems had
changes in the competitiveness
- on a global scale, the N isnt impacting too much...but N deposition is expected in
go up higher
- so far, the area that we are losing biodiversity most has been an area that
has little endemic species
- but soon this will spread
4. Excess N in marine systems
- has a strong effect; N in seas is very limited, if we add it, we will see a bloom in
algea
- the more DIN (dissolved inorganic nitrogen) more plant plancton
- if you add of a limiting resource, species will grow more strongly
- but if you add too much, there will be a crash; it will create anoxia, the lack of
oxygen
- it will effect especially those on the bottom of the ocean
- there wil first be a green algea bloom, as they die, they will fall to the bottom and
decompose; decomposition require oxygen, this will kill fishes and organisms, and
soon the oxygen level will be so low that algea will not like it anymre, then
cyanobacteria will take over the algea,which are toxic to many organisms
- this is observed in the Gulf of Mexico; the excess fertilizer enters the
water; Hypoxic Zone develops
- Hypoxic Zone can be seen globally
- this also effects humans; fisheries; some areas are able to recover, but
may areas have slow or no recovery
- most of this occurs by shore and a little into inshore...but these areas are very
important to many species, since a lot of species spend at least some of thier lives
here (especially when they are young) which are most heavily impacted
B. Climate Change
- flow chartt in all ways climate change can effect us and species; look at how theese individual
peices fit and effect each other
1. Green House effec;
- CO2 accumulates in the troposphere instead of being released into space
- CO2 is not the most polutant greenhouse gas, there are other gases
- the most polutatnt gas (per molecule) is Halocarbones (12000x more
effecitent)
- next is Nitrous Oxide (200x)
- then Methane (20x)
- however, although not too effective as green house, since CO2 is the
most abundant, it is out concern
- the largest amount of CO2 is in marine sediments; all CO2 that has been
consumed by organisms then eventually sunk
- the emmision of other more pllutant gasses are rising as well from the industrial
evolution
2. Climate Change
- graph comparing the average temp puting the 1900 as a starting point, it has risen
by 7degrees
- for global change, it is not only the temp changing but also the weather
- precipitation pattern; in some areas, increase, and some decrease;
ineven ditribution of types of changes
- increase in exrtreme events; heat waves, drought, heavy precipitaion,
tropical cyclones
- we also know that the global warming is to increase
3. Effects on Physiology
- given that CO2 s not a common gas in the atposphere (0.004%), and all plants
access CO2 from the air, then it may make the lives of plants easier
- in an experiment, the plants were exposed to 2x the CO2 levels as 1993
(750ppm vs 375ppm)
- under enriched conditions, most plants increased, but C3 plants had the
biggest effect (least effective type of plant)
- therefore, its not a very big deal...-> the experiement was under
750ppm is ridiculously high
- therefore, it will help plants, but its clearly not enough to
counterbalance the amount we are putting in
- the plants cant take up enough as fast as we are releasing
- the plant growth will level off after a while, after some bit it will not
take up anymore
- the effect of increased temprature on decomposers
- bacterias are important decomposers, and inorder for them to opporate
there is a window of effective temperatures
- they do not opporate well under frozen soils; thererfore, in afreas of
permafrost there are much undecompoased plant materials, but now as
temp starts to increases, the permafrosts melts and there is now a wider
window for the bacterias to decompose