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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 1
BIOS 3010: Ecology Lecture 16: Manipulating abundance:
• Lecture summary: – Manipulating
abundance: • Pest control.
– Pesticides: » Benefits. » Problems.
– Biological control. – Cultural control. – Integrated pest
management. • Culling and harvesting.
– Fixed quota. – Fixed effort. – Sustainability.
Yanomami Indians, N. Brazil (Peter Frey, The Rainforests. A Celebration)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 2
2. Manipulating abundance:
• Represents some of the most important applications of ecology to maintain sustainability in 3 basic ways:
– (1) Pest control - reduction of abundance of “undesirable” species. • e.g. medically- and agriculturally-important insect pests.
– (2) Culling and harvesting of valuable natural resources. • e.g. forests, crops and fisheries.
– (3) Conservation of endangered species. (considered in lecture 24)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 3
3. Pest and weed control:
• “A pest species is any species that we, as humans, consider undesirable”
• This is obviously too subjective, so a better definition is, – “pests compete with humans for cultivated or
natural resources, transmit pathogens, feed on people or their domesticated animals or otherwise threaten human health, comfort or welfare.” This includes “weeds.”
• Of course these are both anthropocentric definitions.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 4
4. Pest and weed control: • Examples include:
– Insect pests of stored food and timber. – Insect vectors of disease, and weeds.
• Agricultural crops worldwide influenced by 8000 weed species, 9000 insect & mite species, & 50,000 species of pathogen.
• The classic pest is an r species. • But some can be K species and they usually have escaped
control by natural enemies because of introduction. • The goal of pest control is to regulate pest populations below the
economic injury level (EIL) (Fig. 15.1a). – EIL is determined by economic balance between cost of control and
benefits of control (Fig. 16.2). – Action should be taken before the EIL to be effective (at the CAT -
control action threshold).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 5
5. Chemical pesticides: • Broad-spectrum insecticides:
– Inorganics (1st generation insecticides): • Salts of copper, sulfur, arsenic or lead (early, persistent, stomach
toxins - required ingestion). – Organics (2nd generation insecticides):
• Botanicals: – Naturally occurring plant products (e.g. nicotine & pyrethrum).
• Chlorinated hydrocarbons: – Persistent, contact poisons affect nerve transmission (lipophilic (fat
soluble) like DDT (dichloro diphenyl trichloroethane) & accumulate in fat) • Organophosphates:
– Also nerve poisons, highly toxic, less persistent (e.g. malathion). • Carbamates:
– Action like organophosphates but less toxic to mammals, although very toxic to bees (e.g. carbaryl).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 6
6. Chemical pesticides:
• Narrow spectrum (biorational) insecticides (3rd generation insecticides): – Microbials:
• Use of pathogens like Bacillus thuringiensis (Bt) to kill pests (bacterial crystalloproteins).
– Insect growth regulators: • Mimic natural insect hormones and enzymes to disrupt
development. – Semiochemicals or “chemical signals”:
• Naturally occurring chemicals (pheromones & allelochemicals).
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 7
7. Chemical pesticides: • Herbicides:
• Organic arsenicals - non-selective organic versions of toxic inorganic compounds like arsenic.
• Hormones - phenoxy weedkillers translocated through the plant selectively.
• Substituted amides - diverse activity. • Substituted ureas - non-selective, pre-emergence (block electron
transport). • Carbamates - like insecticides, but stop cell division. • Thiocarbamates - soil applied, pre-emergence. • Heterocyclic nitrogen - block electron transport - post emergence. • Phenol derivatives - broad spectrum contact chemicals uncouple
oxidative phosphorylation. • Bipyridyliums - fast-acting, destroy cell membranes. • Glyphosate - non-selective, non-residual, translocated leaf application.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 8
8. Problems with chemical pesticides: • Widespread toxicity
– Often nonspecific and applied over wide areas (Table 15.1). – Kill nontarget species which can result in pest resurgence and
establishment of new secondary pests because natural enemies are killed or the pest evolves resistance (Fig. 16.6 & Table 16.2) - the “pesticide treadmill.”
• Biomagnification – Especially lipophilic chlorinated hydrocarbons that increase in
concentration up trophic levels (Fig. 16.5). • Suppressed crop yield
– Pesticides can also be toxic to the crops they protect. • Human health problems
– Especially herbicides such as 2,4,5-T plus 2,4-D (“Agent Orange”) - as carcinogens and teratogens.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 9
9. Benefits of chemical pesticides:
– In terms of lives saved, total food produced, economic efficiency of food production.
• One step ahead of pests – Through effort of chemical companies & increased production.
(Fig. 16.7). • Better & more effective use
– Integrated with improved delivery to target pest. • Benefit:cost ratio remains high
– About $5 benefit for every $1 spent (but biological control has a ratio of 30:1 and cultural control 30-300:1) & >1 billion people have been freed from the risk of malaria.
• Provide unblemished food – In wealthy countries that demand such cosmetics.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 10
10. Biological control:
• The use of natural enemies in pest control (Figs. 16.8 & 16.9) - four types: – (1) Introduction or importation of potentially
effective natural enemies. – (2) Inoculation periodically of a natural enemy
that cannot persist. – (3) Augmentation by repeated introduction of an
indigenous natural enemy. – (4) Inundation by the release of large numbers of
a natural enemy.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 11
11. Cultural control:
• The adoption of practices that make ecosystems unsuitable for pests or more suitable for natural enemies, by: • Crop rotation to reduce resource availability to pests. • Tillage of soil to bury crop residues. • Polyculture by planting multiple crops together to
reduce pest attack. • Trap crops to attract pests away from target crops. • Sanitation to remove crop residues that might harbor
pests. • Variable planting times to avoid pest life histories.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 12
12. Genetic control and resistance:
• Autocidal control: – Release of sterile males
• Genetic selection: – Conventional breeding selection
• Transgenic manipulation of resistant crops:
– Insertion of new genes
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 13
13. Integrated pest management (IPM):
• Combination of physical, cultural, biological and chemical control of pests and the use of resistant crop varieties.
• IPM is ecologically based and the aim is control below the EIL (economic injury level).
• Requires careful monitoring by specialist pest managers and advisors (Fig. 15.2 and Table 16.5).
• IPM is highly desirable - because in the USA before 1945 and widespread pesticide use, crop loss to insect pests was 7%. By 1991, despite a 10x increase in pesticide use, crop loss to insect pests was 13%.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 14
14. Harvesting, fishing, shooting & culling:
– Harvesting can reduce intraspecific competition and so increase yield (Table 16.6) through increased survivorship and fecundity of remaining individuals.
– Maximum sustainable yield (MSY): • Represents the maximum ideal.
– “Fixed-quota” harvesting: • Based on a typical n-shaped recruitment curve
(Fig. 15.7).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 15
15. Harvesting, fishing, shooting & culling:
• “Fixed-quota” harvesting: – High quotas drive the population to extinction – Medium quotas have a single equilibrium
• The MSY (the maximum rate of recruitment) = fragile equilibrium that can shift easily
– Low quotas have two equilibria: • One low & unstable • The other high & stable
– Risky because MSY ignores age structure, habitat variability, or reliability of MSY and fixed quota harvesting commonly leads to extinction (Fig. 16.13).
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 16
16. Harvesting, fishing, shooting & culling:
• “Fixed-effort” harvesting – Can reduce risk associated with fixed quotas
(Fig. 15.9) because equilibria are stable. • As long as effort is not increased to harvest faster
than the MSY can be attained. – But multiple equilibria can lead to extinction.
(Figs 15.11 & 16.16). – Density-independent abiotic events like El Niños
can also influence population crashes (Figs. 16.13 & 15.12).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 17
17. Sustainability:
• “Sustainability has thus become one of the core concepts - perhaps the core concept - in an ever-broadening concern for the fate of the earth and the ecological communities that occupy it.” .... – Begon, Townsend & Harper (2006), page 439.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 18
Figure 15.1a: Pest population fluctuations about an equilibrium abundance above the economic injury level (EIL).
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 19
Figure 16.2 (3rd ed.): Definition of economic injury level.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 20
Table 15.1:
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 21
Figure 16.6 (3rd ed.): Increase in numbers of insect species resistant to pesticides.
see fig. 15.4, 4th ed.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 22
Table 16.2 (3rd ed.):
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 23
Biomagnification of DDD applied to control gnats in Clear Lake, CA.
Figure 16.5 (3rd ed.):
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 24
Figure 16.7 (3rd ed.): Increase in US pesticide production.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 25
Figure 16.8 (3rd ed.): Worldwide increase in use of two biocontrol agents in glasshouses.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 26
Figure 16.9 (3rd ed.): Weevil control of Eichhornia in Louisiana.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 27
Figure 15.2:
Pesticide problems in cotton pests:"(a) target pest resurgence,"(b, c) secondary pest outbreaks"(d) increased pesticide "
"resistance in Lygus bugs."
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 28
Table 16.5 (3rd ed.):
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 29
Table 16.6 (3rd ed.):
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 30
Figure 15.7: Fixed-quota harvesting based on n-shaped recruitment curve.
Unstable equilibrium Stable
equilibrium
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 31
Figure 16.13 (3rd ed.): Harvested declines in (a) Antarctic baleen whales and (b) Peruvian anchoveta.
(See also Fig 15.8 in 4th ed.)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 32
Figure 15.9: Fixed-effort harvesting.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 33
Figure 15.11: Multiple harvesting equilibria for (a) low recruitment at low density (like the Allee effect), (b) density dependent decrease in harvesting efficiency.
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Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 34
Figure 16.16 (3rd ed.): Decline in North Sea herring.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 35
Figure 15.12: Fluctuations in north Atlantic herring populations.