there s enough on this planet for everyone s needs but not enough for everyone s greed gandhi n.
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There’s enough on this planet for everyone’s needs, but not enough for everyone’s greed Gandhi. Overexploitation. Exploitation involves living off the land or sea, using plant and animal products for food, medicine, shelter, fiber, and other products

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There’s enough on this planet for everyone’s needs, but not enough for everyone’s greed Gandhi


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    1. There’s enough on this planet for everyone’s needs, but not enough for everyone’s greed Gandhi

    2. Overexploitation • Exploitation involves living off the land or sea, using plant and animal products for food, medicine, shelter, fiber, and other products • It is the second most important threat to the survival of birds, plants, and mammals • It is also the 3rd most important threat to freshwater fish extinctions

    3. History of Overexploitation • Humans have always been ‘extractive’ by nature and ‘primitive’ societies still largely follow this MO • While much of this appears sustainable, archaeological and paleontological evidence suggests premodern people have been driving species to extinction for 1,000’s of years

    4. History of Overexploitation • Human colonization onto uninhabited islands or continents has typically been followed by mass extinction events of large-bodied vertebrates (e.g. Europe, parts of Asia, N and S Am, Madagascar and many Pacific islands • We have awesome potential to kill (e.g. Passenger Pigeon, bison, and the Pau-Brasil tree)

    5. History of Overexploitation • Exploitation of plants and animals is a large interest not just in developing countries, but everywhere • In the US, it is estimated hunting generates 700K jobs and has an economic impact of $61B (1%)

    6. History of Overexploitation • Impacts of Exploitation • Most activities are directed at a single target species

    7. Exploitation of Target Species • Tropical Terrestrial Ecosystems • Timber extraction is a major threat • Approximately 5.8M ha of tropical forests logged each year (25% world) • Single species approaches (e.g. mahogany) are difficult to compare to other methods, but it is better than clear cutting

    8. Exploitation of Target Species • A discrepancy between high inflation and slow growth rate of tree value creates the situation where cutting all trees irrespective of age is the best economic plan

    9. Exploitation of Target Species • Subsistence Hunting has been around for more than 100K yrs, but consumption has greatly increased • Impact varies tremendously across the tropics • E.g. Sarawak (25K ton), Amazon (74-181K ton), C Af (1-3.7M ton) • Much of this is too high (e.g. C Af is 6x higher than sustainable rates)

    10. Exploitation of Target Species • Hunting rates are unsustainably high across the Congo (solid) and Amazon (open). Extraction rate Sustainable Rate (20%)

    11. Exploitation of Target Species • Subsistence game hunting affects the structure of tropical forest mammal assemblages, as well as other groups through potential cascading effects

    12. Exploitation of Target Species • Nontimber forest products (NTFP) • E.g. fruits, nuts, oil seeds, latexes, resins, gums, medicinal plants, spices, dyes, fibers, and may others • The ethnobotanical studies have catalogued the wide variety of plants used by different groups (e.g. India, 6Kof 16K angiosperms used for traditional medicines, 79% of trees in 1ha of Amazon utilized)

    13. Exploitation of Target Species • The traditional view of NTFP is usually assumed to be sustainable and is viewed as a promising alternative to exploitive practices and/or landclearing • Extractive reserves are one of the of the fastest growing categories of protected areas in tropical forests • The sustainability of these areas is not fully understood at this time

    14. Exploitation of Target Species • However, in tropical rural areas, the combined value of consumption and sale of forest goods may not make them sustainable over longer time periods • A boom in homeopathic remedies has resulted in >150 sp of European plants becoming endangered and extirpation of many local populations

    15. Exploitation of Target Species • Another potential problem is the impact of harvesting on demographic processes and structure • Overharvested populations will succumb to demographic collapse

    16. Exploitation of Target Species • Forestry • Only 22% of the world’s original forest remain in large, relatively natural ecosystems • Most are either boreal (48%) or tropical (44%), with only a fraction of temperate forests remaining (3%) • Many are currently threatened from increased pressure from logging

    17. Exploitation of Target Species • When commercial forestry expands into previously remote, roadless areas, it typically results in high levels of fragmentation of remaining stands • A study of postlogging silviculture on wildlife suggests loss of structure (i.e. snags, woody debris) is particularly important to many species

    18. Exploitation of Target Species • In Fennoscandia, 50% of the red-listed species are threatened because of forestry • In WA, actively managed forests could support 100% of biodiversity whereas timber management on a 50-yr rotation at the landscape level could support a maximum of 87% • Why? Largely structural simplification

    19. Exploitation of Target Species • Hunting of large mammals, small game, and waterfowl are also major target species in temperate regions • Actively managing to increase game animals has proved wildly successful for many species (e.g. deer 500K to 30M) • In TX populations are >3M with 0.5M harvested annually

    20. Exploitation of Target Species • Waterfowl provide another resource to manage at high levels • In 2001, approximately 19.4M birds taken involving 1.6M hunters • While this may provide a skewed view of resources, their habitats frequently aid other species of concern (true of waterfowl, probably not for deer) • Alternative source ($) for landowners

    21. Exploitation of Target Species • Aquatic systems, especially marine fisheries, have been well monitored • Since the 1990’s global catches have leveled off for the first time in history, despite better technology being constantly developed and utilized

    22. Exploitation of Target Species • Trends have leveled off (and fallen) with aquaculture increasing in importance

    23. Exploitation of Target Species • Wild stocks continue to decline due to poor management • E.g. A recent survey of 232 stocks showed 83% over the past 25yrs are on the decline • E.g. Canadian cod 99.9% since 1960’s • By the way, are fish farms a good alternative to wild caught? Are they more productive?

    24. Exploitation of Target Species • There are many species that are targets in the oceans • There are several traits that many vulnerable species in common (easy to capture and biologically least productive) • E.g. occupy shallow waters, form dense shoals in predictable locations, commercially valuable

    25. Exploitation of Target Species • Chinese bahaba is a fish that meets this criteria (frequent byproduct of fishing) • Its bladder is popular for medicinal properties (7x gold) • Relatively late maturity

    26. Exploitation of Target Species • Some of these same traits apply to other groups that make species vulnerable • E.g. abalone occur in shallow waters and species have been harvested from most valuable to least…densities have changed from 1-5K/acre to <1/acre

    27. Exploitation of Target Species • Many freshwater taxa are subject to exploitation for food and other reasons • In 2000, estimated 8.8M tons of inland fish caught (22.4M ton aquaculture) • Economics: in US, estimated 35M spent $38B spent fishing/yr • Europe, estimate 21.3M anglers

    28. Exploitation of Target Species • Populations of 4/7 sp of salmon (Onchorhyncus) listed as endangered • Problem?: • Problem: this may be the most visible fish species in the world • While wild populations are supplemented with hatchery fish, they quickly show divergence (genetically, phenotypically) from wild populations Overfishing and dams

    29. Exploitation of Target Species • Other species are also exploited • During 19th century, M’s of freshwater mussels were collected • However, despite brief respite, currently M’s of kg are exported to Asia • Currently, pollution, dams, dredging, siltation and invasives • In US, currently 72% (of 297) considered endangered with 27 extinct

    30. Impacts of Exploitation on Non-Target Species • There are direct effects of exploitation, but there are also indirect effects • In addition, there may be damage to the environment, causing changes in ‘biological relationships’ or in landscapes or ecosystem functions

    31. Impacts of Exploitation on Non-Target Species • Even logging directed at a single species can ‘puncture’ a hole in the forest • Even highly selective logging operations with modest levels of incidental damage to nontarget trees can generate enough structural disturbance by increasing desiccation and dry fuel loads • Furthermore, mechanized logging itself triggers surface fires

    32. Impacts of Exploitation on Non-Target Species • Can you envision a scenario when loss of large-bodied frugivores may impact forest dynamics? • Seedling recruitment is not clear under different levels of hunting pressure… however, in some heavily hunted forest dispersal can decrease by 60% 90% in some forests

    33. Impacts of Exploitation on Non-Target Species • In temperate regions, loss of large mammals can have deleterious effects • Beavers are ecosystem engineers can dramatically alter the landscape • Recently, they are making a comeback • Loss of Grizzly bears had cascading effects…increasing elk pop(s) and moose, decreasing riparian habitat, reducing songbird populations

    34. Impacts of Exploitation on Non-Target Species • When predators are excluded, some herbivore populations can get extremely abundant, altering plant communities (loss of 95% of a rare orchid in WV due to excessive deer browsing)

    35. Impacts of Exploitation on Non-Target Species • Marine fisheries are estimated to have a global by-catch of roughly 27M tons/yr • How? Trawl fisheries, drift nets and gill nets • Shrimp trawlers (with relatively small mesh size) are estimate to discard 5kg of by-catch for 1kg of shrimp

    36. Impacts of Exploitation on Non-Target Species • Is this just impacting fish? • 19/21 Albatrosses (attempting to eat baited fish) • Can they really be that impactful? • Each boat may set 1,000’s of hooks/day with a total of >250M hooks/yr • It is estimated that 20K sea turtles are caught in the Mediterranean/yr on hooks • Up to 120K sea snakes taken in Aust/yr

    37. Impacts of Exploitation on Non-Target Species • We were talking about the impact of exploitation on non-target species (e.g. by-catch, albatrosses)

    38. Impacts of Exploitation on Non-Target Species • Unfortunately there are many freshwater examples of problems • No individuals caught since 2001 • May reach 300 kg • Only spawn in specific rapids

    39. Impacts of Exploitation on Non-Target Species • Indirect freshwater effects • Salmon bring a huge nutrient load into freshwater systems as they return to spawn and die (8x inc in macroinverts) • Early evidence for a correlation between size of salmon runs from 1924 to 1994 and tree-ring growth rates

    40. Biological Theory to Sustainable Exploitation • Density dependent factors impacting the natural rate of increase

    41. Biological Theory to Sustainable Exploitation • Why should we think populations to be able to withstand the elevated mortality that occurs with most forms of exploitation? • There may be compensatory birth and growth rates to somewhat offset elevated death rates

    42. Biological Theory to Sustainable Exploitation • If a large number of individuals are going to die from one time to the next, is ‘thinning’ the equivalent? • An easy way to approach the question of elevated mortality is to start with the logistic model, which gives the number of individuals at time t as: Nt = Nmax / 1 + ((Nmax/N0 ) – 1)e-rt

    43. Biological Theory to Sustainable Exploitation • Where Nmax is the carrying capacity (which is not stable) • Sometimes biomass is substituted for population size (B for N). Why? Nt = Nmax / 1 + ((Nmax/N0 ) – 1)e-rt

    44. Biological Theory to Sustainable Exploitation • Why should we think populations to be able to withstand the elevated mortality that occurs with most forms of exploitation? • There may be compensatory birth and growth rates to somewhat offset elevated death rates

    45. Biological Theory to Sustainable Exploitation • Why should we think populations to be able to withstand the elevated mortality that occurs with most forms of exploitation? • There may be compensatory birth and growth rates to somewhat offset elevated death rates

    46. Biological Theory to Sustainable Exploitation • Classic logistic population growth to a maximum pop(n) size

    47. Biological Theory to Sustainable Exploitation • The growth of this classic population is • What is the relationship N & Nmax ? • Consider if the pop(n) is being exploited at a steady rate, then its rate of change per unit time (dN/dt) will be the difference between its surplus production and the yield (Y) g(N) = rN (1 – N/Nmax) dN/dt = rN (1 – N/Nmax) - Y

    48. Biological Theory to Sustainable Exploitation • Sustainable yield occurs at 50% of maximum pop(n) size…why?

    49. Biological Theory to Sustainable Exploitation • Stabilities of exploitation • In theory, we have discovered where the MSY occurs • Problem?

    50. Impacts of Exploitation on Non-Target Species • In terms of simple population dynamics, it is the ‘surplus’ that can be removed in any given year • Depending upon population size, that will vary greatly