BIOS 3010: Ecology Lecture 16: Manipulating abundance: 2. Manipulating abundance: 3. Pest and weed control:

Transcription

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 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 1

2 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 2

3 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 & 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 :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

4 10. Biological control: The use of natural enemies in pest control (Figs & 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 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 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 4

5 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 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 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 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 ). Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 15 5

6 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 & 16.16). Density-independent abiotic events like El Niños can also influence population crashes (Figs & 15.12). Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 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 6

7 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. see fig. 15.4, 4th ed. Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 21 7

8 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 8

9 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 9

10 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. Unstable equilibrium Stable equilibrium Dr. S. Malcolm BIOS 3010: Ecology Lecture 16: slide 30 10

11 Figure (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 11

12 Figure (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 12