Other Interspecific Interactions Chapter 7

Interspecific Interactions Symbiosis - intimate association between individuals of different species, in which one lives on or in the other

Interspecific Interactions Commensals - “guests” - neither harmful nor beneficial to the host Use surface of the host as a place to live

Interspecific Interactions Epiphytes - bromeliads, Spanish moss

Interspecific Interactions

Mutualism - relationship of benefit to both organisms Enhanced growth, survival, reproduction in presence of each other (mirror-image of competition?)

Interspecific Interactions Obligate for each (required) Facultative for each (helpful, but not required) Mixture

Culture of crops/livestock Humans and domesticated plants/animals Ants and fungus

Pollination Insects, birds, bats as pollinators Reproduction for plant, food reward for pollinator

Gut Inhabitants Cattle rumen with bacteria Termite gut with protozoans, bacteria

Mycorrhizae Fungus and root tissue Fungus increases water, nutrient uptake Plant root supplies organic carbon

Algae & Animals Hydra with Chlorella Coral with dinoflagellates (side effect of photosynthesis is precipitation of calcium carbonate)

Lichens Fungus and algae Fungus absorbs water, nutrients Algae photosynthesizes, provides organic carbon (algae often in obligate relationship)

Interspecific Interactions Parasitism - obtains nutrients from one or few hosts Normally causes harm, but not death Often includes pathogens (disease- causing), viruses Superabundant - > half of species on earth

Microparasites Bacteria, viruses, protozoa, fungi Multiply directly within host (usually within cells)

Microparasites Transmitted directly from host to host (VD, influenza) Transmitted by vector (some other animal) (malaria, sleeping sickness)

Macroparasites Flatworms, roundworms, insects Grow in/on host, produce infective stage that leaves, live within body cavities or intercellularly

Macroparasites Transmitted directly (intestinal nematodes, lice, plant fungi) Transmitted indirectly (tapeworms, flukes)

Transmission Transmission rate depends on host density Rate increases with density (susceptible hosts only - genetics)

Distribution Distribution is clumped (site-specific) Few hosts have large numbers, most have none High intensity of infection, low prevalence

Response of hosts Die in whole or in part Biotrophic parasites require living hosts Necrotrophic parasites prefer dead hosts (pioneering decomposers)

Plant hosts Infected cells die immediately - hypersensitivity Surrounding cells produce phytoalexins to prevent spread of parasites

Invertebrate hosts Phagocytic cells engulf foreign particles

Vertebrate hosts Immune responses - several types of killer cells with “memory” Inhibits future infection by same things Response most effective for bacteria, viruses Response least strong for macroparasites, protozoans

Bottom Line Reduced survival, growth, fecundity, competitive ability of host Some evidence that parasites may be chief factors controlling populations of some organisms (e.g., humans)