Predation Great White Shark and Fur Seal. Plant defenses are developed at a cost to fitness when: 1. Organisms evolve more defenses if they are exposed.

Predation

Great White Shark and Fur Seal

Plant defenses are developed at a cost to fitness when:

1. Organisms evolve more defenses if they are exposed to much damage and fewer defenses if cost of defense is high

2. More defenses are allocated within an organism to valuable tissues that are at risk

3. Defense mechanisms are reduced when enemies are absent and increased when plants are attacked - mostly true for chemicals not structures

4. Defense mechanisms are costly and cannot be maintained if plants are severely stressed by environmental factors

Pine beetle infestation – British Columbia

Pine Beetle and Pitch Tube

Serengeti Grazing System

Serengeti Grazing System

Serengeti Grazing System

Grazing facilitation

• Grazing facilitation occurs when the feeding activity of one herbivore species improves the food supply for a second species

Opuntia stricta – prickly pear

Prickly pear infestation in Australia

Area infested with prickly pear before biocontrol

Same area after biocontrol

Biocontrol Agent – Cactoblastis cactorum

Symbiosis

Symbiosis

• Symbioses - species living in close association

• Parasitism +,- parasite benefits, host harmed

• Commensalism +,0 or 0,0 can have positive effect for one species or for neither

• Mutualism +,+ both species benefit

Gopher Tortoise – Commensal Host

Gopher Tortoise Distribution

Epiphytes

Bird’s NestFern

Nalini Nadkarnistudying epiphytes

Epiphytes

Figure 1: Hypothetical tree illustrating how vascular epiphytes in humid forests tend to partition substrates illustrating sensitivity to micro climate, particularly humidity, and associated development of the organic rooting media required by some populations.

Parasitism and Disease

Lyme Disease Cycle in the UK

Parasitism

• Parasitism - intimate association between two species in which the parasite obtains its nutrients from a host - parasite usually causes some degree of harm to its host - either reduced growth or reproduction

• Pathogen – disease causing agent

• Disease – abnormal condition of host due to infection by a pathogen that impairs physiological functioning

Parasites on Plants

Insects are green,Fungi are brown,Worms are blue,Protozoa are yellow

Parasitism occurs on a continuum from:

• ectoparasites - live outside hosts body and experience same conditions as host - ticks, mites, fleas, aphids

• endoparasites - live inside host's body cavity - buffered from outside conditions - tapeworms, flukes

• intracellular parasites - live inside individual cells of the host - viruses, bacteria, protozoa - often called microparasites

Or another way to divide parasites:

• microparasites - viruses, bacteria, protozoa - small, often live intracellularly, main point is that they reproduce in host and will have very large numbers in host

• macroparasites - tiny to very large - nematodes, tapeworms, flukes - larger individuals that grow in host but multiply by producing infective stages that are shed by host to environment where they infect new hosts

Parasite Transmission

• Direct transmission – from one host to another of the same species via air, water, coughing, blood, feces, etc.

• Indirect transmission – from one host to another of the same species via another species called a vector

• Vector – species which transmits parasite or pathogen from one host to another

Microparasites Macroparasites

Direct transmission

HIV virus,Amoebic dysentery,Mildews on plants

Lice, fleas, ticks, aphids, hookworm, pinworm,mistletoe

Indirect transmission

Plasmodium (mosquito),Plant viruses (aphids),Trypanosoma (tsetse fly)

Tapeworms,Schistosomes (snails),Rust fungi

Powdery Mildew on Grape Leaf

Powdery Mildew Life Cycle

Head Lice and Life Cycle

Mistletoe

Mistletoe Life Cycle

Malaria disease cycle

Schistosomiasis - Life cycle of the schistosome worm

Worldwide incidence of schistosomiasis

Worldwide incidence of schistosomiasis

Rust Fungus Canker

Rust Fungus Life Cycle

Two ways to study parasite numbers

• Prevalence – percent of host population that is infected – best for microparasites

• Intensity – number of parasite individuals per host – usually best for macroparasites

Frequency of infection

Parasites usually occur in aggregated distributions – due to 4 possible factors:

1) random colonization events followed by asexual reproduction in hosts that do get parasitized

2) environmental "hot spots" where parasite eggs and infective stages survive well

3) dispersal constraints - geographic or behavioral barriers limit dispersal of parasites to just a few hosts

4) variation in susceptibility of individual hosts - due to nutrition, genetics

European rabbits as pests in Australia - 1938

Introduced pests in Australia – red fox, rabbit, cat, pig, & goat