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Lecture

BGYC63 Sept27


Department
Biological Sciences
Course Code
BIOC63H3
Professor
Ivana Stehlik

Page:
of 4
Sept27 BIOC63
Herbivory Lab
- data will be uploaded
- download it
- do stats yourself (instruction in lab mannual) or Lanna will help in 2nd lab slot (LG2) in room TBA
on black board
- therefore, BOTH LAB GROUPS will submit at the same DEADLINE (LG2)
Threats to Biodiversity
Terrestrial Ecosystems vs Aquatic Ecosystems
- trying to see what threats to biodiversity is the most important in these two environments
- for terrestrial, land use change....so habitat destruction, then climate change
- biotic exchange is when there are alien species introduced
- for aquatic ecosystems, before, the main threat was fishing..but now, climate change
Terrestrial Ecosystems
**5 Biome specific threats to Biodiversity ** (look at chart)
- Land use, Climate, Nitrogen deposition, Biotic Exchange, Atmosphere CO2
- these 5 drivers happen on a different level and importance across different
ecosystems!
- Land use has the most vulnerability because withiout the land, there is no way to
live
1. Overexploitation
Definitions
Sustainable exploitation: using plants or animals so that they dont run out (exploitation
rate< replenishment rate)
the natural ecosystem must be able to still function healthily
there must be NO degration of genetic diversity, NO permanent
alteration of size distribution, age structure or sex ratios, Retantion
of social behaviour
Overexploitation: our use of what ever we take out, consumptive, is lost, and gone forever
the rate of use exceeds rate of renewal; likely extinction
occurs when the item we are exploiting has no substitution (the rarer, more
money)
eventually, the local isolated population will go down-> local extirpation
(extinction in given area) -> global extinction
Reasons for overexploitation
i) Food
- human driven extinction...wherever human appear, megafaunas (large animals)
are usually driven to extinction
- so easily hunted, because megafaunas had no natural enemies
- Passenger pigeon; best known and recorded extinction...and was soo abundant
before! (flocks were 3-5km); since the traveled in such huge flocks, easy game and
food (meat and egg); with railways and tellegraphs people can communicate for
location of flocks and sell the meat in large areas
- once the population started to decline, it was very fast...(since they were
scattered, could not breed)
- extinction can be a threat to any species, no matter how abundant they
are
ii) Pet Trade
- tropical fish caught for pet; 30-40% caught wild fish die; the composition of
local
population are dramatically changed, when fish are breeded in an area
for pet( in areas close to coast, the fishes that are supposed to be most
abundant, are gone)
- bird exploitation is similar
iii) Medicine
- we have already talked about the Silphium for birthcontrol
- Yew (type of tree); one of the best examples
- found that the Yew was effective agiainst cancer; however, the
concentration
of the "medicine" part was low (needed 3 300 year old trees for
1g) but the pressure for it was so high
- but the spotted owl was dependant on old yews
- environmantalists fought, and program was stopped
- later on, found that the common yew had higher concentration
of the
"medicine" plus, for this, people knew how to grow
- now was can create taxol
- American ginseng
- used highly in chinese medicine
- the problem is that the the "medicine" part is in the root and not
leaf...you
have to take the whole thing (older the better)
iv) Trophy Hunting
- bigger and fearcer the better
- it changes strongly thr composition and function of the remaining
population (Artificial
Selective Pressure)
- animals will start to become sexsually mature earlier and smaller,
cause the bigger
ones are removed
- since the larger the weapon the better (horns etc) smaller ones are
selected
- altered migration rates (if they migrate in a predictable way, can be
caught) -> lowerd
mating
- ex) tusks for elephants are now smaller
- ex) sockeye salmon; the longer and higher they are, the sexier...but we
take these
large males because they have more to eat; the average male
phenotypes has changed...lowered the sexual success
- ex) colour morphs in red foxes in Canada
- the silver foxes are most desired for fur, so its abundance has
changed; but
we dont know if the species is worse off or not (because the red
fox is increasing vs decreasing silver fox)
- typically the most dominant male is removed by the hunters (adult
female condition
goes down, and so does the amount of children)
- for deers, you can predict at an early age, which ones will turn into
better ones...so
take out the "bad" young
INDIRECT effect of Overexploitation
- Dodo bird (easy to catch) was driven to extinction
- the Dodo bird cracked the seeds of the Tambalacoque tree
- no found young Tambalacoque trees since the dissapearance of the
Dodo bird
- if you take out the Keyston species, like wolves, also has a small biomass has a
great impact
on other species (the herbivores will do too well and will dimish the plants
(producers))
Effects of overexploitation
2. Habitat
- destruction of mangroves due to deforestation....fish cant produce infants
-Hydroelectric dams -> takes away the wetland changes the migration patters of wild
animals
i) Fragmentation
- disected by roads, skii sites
- areas are moe and more disconnected
- "island" effect, the larger the island size, the more species you will find
- also the distance to the island pieces to the mainland is
important to how
fast the species can comeback is population is lost in the island
- so whats the problem with fragmentation?
- the productivity the unit was strongly influenced by the species
diversity
within that community
- therefore, the more diverse the better, and the larger the area,
the more
diverse
- nutrient cycling by the dung beetles
- was faster and richer in non-fragmented areas
ii) Edge effect
- the size of the edge is very predictable; the conditions in the edge is
very different
from the edge and the contents
- with habitat fragmentation, all the conditions are more represented by
the conditions
of the edge
- example, hotter in the edge, more wet, etc
- found that the inccidents of fire were higher in highly irregular shaped
forests (more