BIOS 3010: Ecology Lecture 16: Manipulating abundance: •

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.


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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 (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).



•   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).


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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.


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 (3 rd ed.) : Definition of

economic injury level.


Table 15.1:


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

7

Table 16.2

(3 rd ed.)

:


Figure 16.5

(3 rd ed.)

:

Biomagnification of

DDD applied to control gnats in

Clear Lake, CA.


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

pesticide production.


8

Figure 16.8 (3 rd ed.) : Worldwide increase in use of

two biocontrol agents in glasshouses.


Figure 16.9

(3 rd 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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Table 16.5

(3 rd ed.)

:


Table 16.6

(3 rd ed.)

:


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

10

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.)


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

(3 rd ed.)

: Decline in

North Sea herring.


Figure 15.12: Fluctuations in north

Atlantic herring populations.


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BIOS 3010: Ecology Lecture 16: Manipulating abundance: •

BIOS 3010: Ecology

2. Manipulating abundance:

3. Pest and weed control:

4. Pest and weed control:

5. Chemical pesticides:

6. Chemical pesticides:

7. Chemical pesticides:

8. Problems with chemical pesticides:

9. Benefits of chemical pesticides:

10. Biological control:

11. Cultural control:

12. Genetic control and resistance:

13. Integrated pest management

(IPM):

17. Sustainability:

Table 15.1:

Table 16.2

:

Figure 16.5

:

Figure 15.2:

Table 16.5

:

Table 16.6

:

Figure 15.9: Fixed-effort

harvesting.

Figure 16.16

: Decline in

North Sea herring.

Figure 15.12: Fluctuations in north

Atlantic herring populations.

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BIOS 3010: Ecology Lecture 16: Manipulating abundance: •