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weed seed dispersal mechanisms

Specialized seed structures affect whether, and how, animals spread seed:
-burrs: cocklebur, sandbur seed
-appendages: beggarticks seed

Selection for time of seed release: adaptation for quick or slow release from parent plant?
-quick release: oversaturate predator demands of feeding and leave enough after that for new colonizers
-slow release: maximize chance some seeds land on ground during favorable time for quick germination or escape from predators

Differences in time:
-seed ripens on parent plant
-seed retained on parent before its dispersed (seed shattering)
-example: weeds with long flowering period and corresponding long period of ripening and release: seed shatters immediately after ripening on parent
-example: weeds flowering and seed production in narrower time period, often require harvesting activity to release seed: evolved with crop, maximize chance of dispersal with crop

Animal behavior affects where the moved seed ends up, and its success thereafter:
-the territorial and migratory behavior of animals dispersing seed
-animal feeding (eating, digestion) affects seed viability
-animal storage of seed: distance, concentration, location;

The Role of Animals in Dispersal

Human dispersal
-new continent, region invasions
-local dispersal: machinery, crop seed contamination

"Tumble Weeds: movement of parent plant (with seeds) on ground after dispersal, -blow with wind;
-seeds dispersed in rolling action;
-examples: kochia on mother plant, forms rolling ball;
-velvetleaf capsules

Specialized mechanisms of some weed species to bury themselves: wild oat hygroscopic awns that twist themselves into the soil (self-seeding)

Seed Dispersal: Non-animal

Poverty of seed fall in the immediate neighborhood of the parent characteristic of of plants in isolation; e.g. mullein, musk thistle is pasture

Ants play important role, especially in storage concentrations

bolochorous: seed dispersed by the agency of propulsive mechanisms

: seed dispersed by the agency of animals; synonymous terms: synzoochorous; zoochorous

Ants play important role, especially in storage concentrations

barachorous seed: dispersed by its own weight; synonymous term: clitochorous

Reading assignment: Harper: Ch. 2: pp. 33-60; summary p. xiv