Keystone Species

Consumers (predators, herbivores, parasites, and diseases) that maintain food-web diversity.

Anolis: Two species/island

7 Islands: 2-fold body size difference (males)

Reduce competition for food?

St Maarten: Greater overlap?

WHY? Schall, J.J. 1992. Oecologia 92:58-64.

Malaria: Insect-borne infection

• Initially (?) Intestinal parasite of reptiles

• Became infection of blood

Accessible to biting insects

• Vector-borne parasite with complex life cycle

Saurian malariaInfection reduces a female’s clutch size:

Fitness cost of infection

Significant in 4 of 5 years

Infected males: Less capable of evicting intruders on feeding territory

Fitness Cost of Infection

Correct for increase in clutch size as female size increases

Report: Loss of 2 eggs/year due to malaria

Spatial distribution

Smaller lizard not found at lower elevation: exclusion

Smaller lizard common in central hills: 2 species coexist

Biting sand-fly found in central hills: vector of saurian malaria

Malaria, “keystone predator”

Central hills: malaria infects 30 – 46% of the otherwise competitively dominant species

Infects only 3.6% of A. watsii, smaller species

Differential fitness cost of disease (parasite) maintains host diversity

Generalized keystone predator

Keystone predator’s diet in two-prey environment:

Dietary frequency of more common prey exceeds that species’ environmental frequency

Keystone predators

“Zebras attracted to lethal anthrax grass”

Dr. Wendy C. Turner

Biol. Sci.

Etosha/Namibia

10

Equus quagga

Anthrax – Zebra – Plants + FLP - Anthrax

11

Bacillus anthracis

Obligate Killer; Environmentally Transmitted

Vegetative Spores: Persistence

Infective Dose?Zebra Immunity and Macroparasites?