- Exploit the resource until the marginal costs equal the returns. Some resource will remain because it is not “economical” (rational) to continue the exploitation.Why this will protect oil but maybe not biodiversity??o In the case of wild species, there are special problems with this exploitation strategy.  Rate of exploitation must be less than rate of natural increase Population must remain above minimal viable size Population must retain its functional ecosystem role Genetic diversity must not be degraded Size distribution, age structure, sex ratios must not be permanently altered Social behavior must be retained ex: Red deer hunted to lower the number of males Red deer important social structure so if you remove male deer, the average and frequency goes way down for the remaining male deer. ex. Ider duck down form really dense flocks the ducks have high heat content but if the population is decreased then the heat content goes down and they are not able to melt ice (allele effect) *(the last three= Darwin’s debt)- Economic factor o lotka voltaire curve: maximum sustainable yield? inflection point o Cost per effort may reduce harvest below maximum sustainable yield or technology may raise harvest above maximum sustainable yield o Tyranny of small decisions: there is a big problem when small increase in harvest has a slow but serious consequence (this occurs in situations where a number of decisions, individually small in size and time perspective, cumulatively result in an outcome which is not optimal nor desired)Overexploitation can occur in several different instances such as... o water (ex. contamination) o soil (ex. erosion) o organisms o ecosystems - Definition of overexploitation (wild species are special cases which can’t continueto be exploited or Darwin’s death will ensue.) o the rate of use exceeds the rate of renewal o the use is consumptive (meaning it is lost) o the excess rate of use leads to...  loss of the functional role of the population, community, or ecosystem there is a failure to renew things that are exploited unless there is intervention  extinction becomes more likely for organisms that are overexploitedo In the case of ecosystems...  ex: wildlife refuge in West Kansas how often to use fire to maintain population or allow deforestation... could shift from a forest to a grassland system. Invasive species of grass have an impact on the system  exploitation is a form of disturbance  when the disturbance exceeds the resiliency of the ecosystem... overexploitation occurs (overexploitation frequency, scale, and intensity--> determines whether the ecosystem is pushed past its resiliency level)  different disturbances can have independent or additive effects  a new kind of ecosystem may result if overexploitation continues within a system - Overexploitation occurs when …. (Know these) o there are no substitutes (rarity= higher value) investments in new harvesting techniques often drives the populations even lower. (ex: can-opener can be substituted by a pocket knife or an electric can-opener, but in the case of bluefin tuna there is no substitute so the fish is highly valuedand overharvested) o stewardship values are weak o impoverished people have few alternatives (need for tree cutting for cooking fuel (Africa), etc. causes them to exploit the resources which they have available) → possible solution to cooking alternative would be solar powered cooking methods o we often don’t know when we are reaching limits (ex: oceanic fisheries) - Renewable resource management o pure commons free for all o complete closure o area allotment (blue crab, morel mushroom... informal) (halibut fisheries... formal) o constant quota (fish caught, deer shot) o proportional quota: harvesting done in proportion to the rate of renewal for the organism to ensure that overexploitation does not occur (changes in population size determines) o Individual Transferable Quotas (these are a form of proportional quota) (trade or sell quotas)  pine martin example  they are trapped in Canadian woods for their valuable fur (the value of the fur causes increased harvesting … another example of there not being a substitute)  There have been changes in quota numbers depending on the number of young birthed in the previous year (rate of renewal determines quota)- Great whale protection began in late 1970s o Blue whale: largest vertebrate ever lived  were feeding further offshore  birthing young in specific place (Costa Rican Dome) High food concentration o Fin whale: has seen a 3% increase per year in some places o Sperm Whale: remain low  feed on large squid specific food source o Sei Whale: decreasing population - There has been indirect exploitation by way of whales killed by entrapment in commercial fishing nets - There have been tropical forest losses due to excessive timber practices (greatest decline in Africa) o they need this energy to cook, etc. fuel wood is the cheapest way to get energy and this drives the loss of forest (electricity costs about 34 times the cost of fuelwood) solar cookers proposed o in tropical countries forest land converted to cattle pasture and plantation agriculture - In Latin America: Mahogany is sold (a single tree $100,000 worth of lumber) o Mahogany sold in the US creates $100 million market) o most of the large trees inside parks and protected land o Madre de Dios (“protected” indigenous reserve in Southern Peru): after removal illegally of trees, gold miners came into the reserve to mine  Financial uncertainty in the US and Europe drives up gold prices and this led to destructive gold mining and mercury contamination o Why can’t we grow mahogany trees in plantations?? Insect won’t let us, they burrow into the trees and destroy the apicaldominance and causes branching (Mahogany Shoot Borer) o Is sustainable harvest possible? Positive aspects wind pollinated and wind dispersed seeds  seeds are not an important food source  wide spread  Negative aspects  overexploited everywhere, hard to get adequate volume  slow growing, rate can be improved by removing vines  Shoot borer moth (one larva can ruin the timber value of the whole tree)  can’t be grown in plantations  no chemical or biological control for moth so far - Blue fin tuna: one of the largest predators in the ocean o they form schools so multiple catches are typical o