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

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 • 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

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

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)

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%)

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

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

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

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)

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

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

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)

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

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

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

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

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

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

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

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

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

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

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?

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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