Species Interactions (cont.) Chapter 15
1. Disease
Assoc. b/t pathogenic microorganism & host; host suffers physiologically.
2. Parasitism
One spp. lives in obligatory assoc. with another, metabolically depends host
3. Pest Control (Applied Problems Series)
Chemical, Biotic, Genetic control of species cause harm
4. How does Disease affect populations?
(1). Effects on reproduction � limited amount energy
-Limits reproductive output
-Example malaria parasites majority 125 spp. lizards
-Western fence lizard 25% malaria 20% reduction clutch
-Example bird chicks frequently attacked nest parasites
-Colonial nesting birds prone ectoparasites ease transmission
-Cattle egrets Queensland Australia-ticks & arbovirus carry
(2). Effects on Mortality � What proportion mortality assoc. disease.
-Dead harbor seals North Sea 1988?
-Spread other areas N. Sea 60% of population 50,000
-Epizootic=a disease epidemic among wild animals
What proportion mortality associated with disease-Did it last in the population?
-Viral disease suspected- symptoms resembled canine distemper.
-Morbillivirus (phoncine distemper virus)
-In 2 weeks seals died pneumonia 2nd bact. & viral infections.
-Caused pregnant females to abort- more prevalent virus males
-Proximity to other colonies best predictor variable not density
-Survivors immune � new pups each year susceptible 20% population
-Compartment model showed this 1988 epizootic could not be maintained
-Phocine distemper virus found harp seals rarely overlap range of harbor seals
-1988, 89 crossed into North Sea large numbers, perhaps infecting harbor seals
-Harbor seals have recovered to pre-1988 epizooic
5. How often do diseases exert long-term effect on populations?
-Most studies disease agricultural populations cattle etc.
-Brucellosis in ungulates highly contagious bacterium
-Prevalent cattle throughout world �contagious abortion�
-Controversy transmission to cattle bison & elk in West.
-Measure Seroprevalence - % indiv. host pop. with antibodies
-Seroprevalence to brucellosis Yellowstone National Park 1990-91
6. Threshold densities of host allow disease to sustained in population
-Perhaps strategies devised to cull individuals or vaccinate %
-Bison herd >200 individuals critical threshold epidemiology principle
-Brucellosis will persist in populations >200 Yellowstone 4000 animals
-Brucellosis could infect small pop. bison-once passed not maintained
7. Rabies � Oldest known diseases 500 BC
-Viral infection of central nervous system mammals
-Common (fox, wolves, coyotes, skunks, raccoons, jackals, bats)
-Domestic dogs primary vector to humans � no cure!
-Bats in caves account for 90% of 26 cases died US
-Rabies vectors differ across the US various genotypes of viruses Lyssavirus genus
-Rabies vectors differ across the US changed over time
8.. Epizootic of rabies in eastern US 1970s- spreading ~30 yrs
-Diseased raccoon brought in humans
-Now in US and Canada
-Attempt vaccinate wild raccoons � recombinant virus vaccine 1997
-Bait fish oil & wax polymer contains oral vaccine
9. Europe fox is the major vector of rabies-1939 Poland moved 20-60 km/yr
-Tried culling program � reproductive rates are too fast fox
-Started vaccination program successful 1999 rabies highly reduced or absent
-Number individuals need vaccinate function of density
-Use compartment model again to understand rabies outbreak
-This model supports the cyclical nature seen in rabid foxes
-Rabies Europe cyclic � France have a 4-5 yr cycle
10. Evolution of host-parasite system: Who would win the arms race?
-The parasite evolves much faster (higher turnover rates)
-The host evolves much slower-need have genetic variability
11. Study evolution of host-parasite systems serial passage experiments Lab
-Disease org. transferred one host to another
-Holding host properties constant
-Following the evolutionary changes in disease organism
-Developed for vaccine studies
-Used for evolution of virulence
12. This increase in virulence in the lab does not occur in natural disease systems
-This is thought to be the result of host genetic variability
-In comparison to the simple genetic structure parasite
13. Red Queen Hypothesis
-Any evolutionary adjustment that a species makes can be countered
by natural selection by other species in a community.
-Example: Disease-host, plant-herbivore, predator-prey systems
-The species run, run, run but get nowhere increased fitness balances out.
-Red Queen Hypothesis thus predicts changing evolutionary
dynamics between host-parasite not a stable equilibrium.
14. Summary:
-Disease major species interaction
-Advances in this field primarily study of human health epidemiology
-Mathematical models of host-parasite systems utilize compartment models
-Simple models show threshold density below which parasite dies out
-Research focused on how move host population below this threshold
-Disease and parasites can cause reduced production or mortality
-Parasites and host are locked in arms race to maximize fitness
-One main factors limiting disease virulence host genetic variability
-Thus, monocultures crops or clonal populations >susceptible virulent disease
Chapter 18
15. Pest Control � Micro and macro-parasites (pests) Human perspective
-Pest control agricultural systems 1o use toxic chemical (pesticides)
-2.5 billion kg (5 billion lbs) used annually world-wide control pests
-Despite effort ~48% world�s crops lost to pests; no gain last 60 yrs
16. Pesticides are a short-term solution:
(1) Pesticides have detrimental effects on many organisms (DDT)
Rachel Carson (Silent Spring, 1962)
(2) Many pest spp. genetically resistant chemical killed them before
Cotton crops in Central America, Mexico, Texas
(3) Toxic chemicals produce pest problem- destroy insect parasites & predators
17. How can we achieve pest control without these problems?
4 Primary strategies for dealing with pests:
(1) Natural Control � Exposed to natural predators, parasites, disease, competitors
(2) Pesticide Suppression � Treat with herbicides, fungicides, insecticides, poisons
(3) Cultural Control � Crop rotation, strip cropping, burning crop residue, staggered
(4) Biological Control � Introduction predators, parasites, disease; genetic manipulation
18. IPM - Integrated Pest Management: Use of all 4 strategies
Goal: Reduce pest damage minimize pesticide & maximize natural control
19. Idea behind Biological control � maintain pest below economic threshold
-Use introduced predator to lower density pest
-Assumption never going to get rid of all pest
-Agricultural systems promote pests (monocultures, optimal habitat)
20. Example of biological control: Cottony-Cushion scale on citrus CA
-1887 whole citrus industry threatened southern CA
-Tried cyanide & other chemical sprays failed
-Entomologist sent Australia meeting
-Sent back parasite & predaceous ladybird beetle (vedalia)
-1 year after release 10,000 beetles all scales gone
-When DDT used citrus groves � scales returned
21. Different Example of biological control: Genetic control
-Crop plant genetically manipulated increase resistance
-Selective breeding done with care: get unwanted results
-breed out chemical toxic to animals in animal feeds
-breed in physical charac. less damage herbivores
-arms race of pathogen/herbivore with plant geneticists
-Bioengineering whole field direct & indirect manipulation genes
-directly into plant genome-resistance gene
-indirectly into bacteria naturally found on plant
-Pests genetically manipulated sterile or less vigorous
22. 2nd Different Example of biological control: Immunocontraception
-Idea is to reduce fertility of pest
-Antigens of egg surface proteins (zona pellucida glycoproteins; ZPG)
-Prevent sperm from attaching to surface egg & thus fertilization
23. Best approach is to use Integrated Pest Management System
-Need understand ecology of pest integral component of successful biotic control
and give us understanding of when chemicals are successful or not
24. Summary:
-Pest are species interfere with human activity (economics)
-Traditionally utilized pesticides to control pests
-Problems with this approach led to more use of biological controls
-Biological control has been successful and also >failures
-Need better understanding of pest-host systems successful
-Advent of biotechnology may increase success varied biological controls
-An integrated system of pest management great promise