Download pdf - BIOS 3010: Ecology Lecture 16: Manipulating abundancehomepages.wmich.edu/~malcolm/BIOS3010-ecology/Lectures/L16-Bios3010.pdf• The goal of pest control is to regulate pest populations

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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)


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)


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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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).


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).


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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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.


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.


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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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.


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.


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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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%.


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).



•  “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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•  “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).


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.


Figure 15.1a: Pest population fluctuations about an equilibrium abundance above the economic injury level (EIL).

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Figure 16.2 (3rd ed.): Definition of economic injury level.


Table 15.1:


Figure 16.6 (3rd ed.): Increase in numbers of insect species resistant to pesticides.

see fig. 15.4, 4th ed.

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Table 16.2 (3rd ed.):


Biomagnification of DDD applied to control gnats in Clear Lake, CA.

Figure 16.5 (3rd ed.):


Figure 16.7 (3rd ed.): Increase in US pesticide production.

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Figure 16.8 (3rd ed.): Worldwide increase in use of two biocontrol agents in glasshouses.


Figure 16.9 (3rd ed.): Weevil control of Eichhornia in Louisiana.


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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Figure 15.7: Fixed-quota harvesting based on n-shaped recruitment curve.

Unstable equilibrium Stable

equilibrium

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Figure 16.13 (3rd ed.): Harvested declines in (a) Antarctic baleen whales and (b) Peruvian anchoveta.

(See also Fig 15.8 in 4th ed.)


Figure 15.9: Fixed-effort harvesting.


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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Figure 16.16 (3rd ed.): Decline in North Sea herring.


Figure 15.12: Fluctuations in north Atlantic herring populations.