BIOS 3010: Ecology Lecture 16: Manipulating abundance: •

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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.

Dr. S. Malcolm

Yanomami Indians, N. Brazil (Peter Frey,

BIOS 3010: Ecology

The Rainforests. A Celebration

Lecture 16: slide 1

)

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 2

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.

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 3

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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 ).

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 4

5. Chemical pesticides:

•   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

6. Chemical pesticides:

•   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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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 7

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 8

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.

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 9

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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.

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 10

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 11

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

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 12

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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%.

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

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 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

Table 15.1:

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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Table 16.2

(3 rd ed.)

:

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 22

Figure 16.5

(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

Figure 15.2:

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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Table 16.5

(3 rd ed.)

:

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 28

Table 16.6

(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

Figure 15.9: Fixed-effort

harvesting.

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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Figure 16.16

(3 rd ed.)

: Decline in

North Sea herring.

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 34

Figure 15.12: Fluctuations in north

Atlantic herring populations.

Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 35

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