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.
Dr. S. Malcolm
Yanomami Indians, N. Brazil (Peter Frey,
BIOS 3010: Ecology
The Rainforests. A Celebration
Lecture 16: slide 1
)
• 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 2
• “ 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.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 3
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• 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 4
• Broad-spectrum insecticides :
–
Inorganics (1 st generation insecticides):
–
• Salts of copper, sulfur, arsenic or lead (early, persistent, stomach toxins - required ingestion).
Organics (2 nd 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 5
• Narrow spectrum (biorational) insecticides
(3 rd 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).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 6
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• 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 7
• 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 8
– 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.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 9
3
• 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 10
• 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 11
• Autocidal control:
– Release of sterile males
• Genetic selection:
– Conventional breeding selection
• Transgenic manipulation of resistant
crops:
– Insertion of new genes
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 12
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• 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 13
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 14
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).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 15
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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 16
• “ 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 17
Figure 15.1a: Pest population fluctuations about an equilibrium abundance above the economic injury level (EIL).
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 18
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Figure 16.2 (3 rd ed.) : Definition of
economic injury level.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 19
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 20
Figure 16.6 (3 rd ed.) : Increase in numbers of insect species resistant to pesticides.
Dr. S. Malcolm BIOS 3010: Ecology see fig. 15.4,
4th ed.
Lecture 16: slide 21
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(3 rd ed.)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 22
(3 rd ed.)
Biomagnification of
DDD applied to control gnats in
Clear Lake, CA.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 23
Figure 16.7 (3 rd ed.) : Increase in US
pesticide production.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 24
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Figure 16.8 (3 rd ed.) : Worldwide increase in use of
two biocontrol agents in glasshouses.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 25
Figure 16.9
(3 rd ed.)
: Weevil control of
Eichhornia in Louisiana.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 26
Pesticide problems in cotton pests : "
(a) target pest resurgence, "
(b, c) secondary pest outbreaks "
(d) increased pesticide "
" resistance in Lygus bugs.
"
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 27
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(3 rd ed.)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 28
(3 rd ed.)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 29
Figure 15.7: Fixed-quota harvesting based
on n-shaped recruitment curve.
Dr. S. Malcolm
Unstable equilibrium
Stable equilibrium
BIOS 3010: Ecology Lecture 16: slide 30
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Figure 16.13 (3 rd 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 31
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 32
Figure 15.11: Multiple harvesting equilibria for (a) low recruitment at low density (like the Allee effect), (b) density dependent decrease in harvesting efficiency.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 33
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(3 rd ed.)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 34
Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 35
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