competition

What a wondrous problem it is, what a play of forces, determining the kind and proportion of each plant in a square yard of turf!!

10.1 Relationships between yield of dry matter (g) and plant density for two pasture plants At some point, individuals start competing for resources. Greater density of seeds does not = greater total, final, dry weight. Increasing soil fertility = greater final biomass…but that is also density dependant. Do you see why??

10.2 Average individual plant weight (g) for Trifolium subterraneum At some point, individuals start competing for resources. Variable are density and time. Do you see why??

10.3 Frequencies of dry weights of individual seedlings of Tagetes patula Timing is everything!!

10.5 The effect of relative order of emergence on seedling dry weight (mg) Timing is everything! If you emerge first you have a big advantage. Asymmetric competition Role of propagules & regeneration niche

10.7 A transect through a natural population of Myosotis micrantha Competition, but…for what? And, how? Neighborhood concept…

10.8(A) A strangler fig, (B) Pueraria lobata Direct competition…wrestling!!

10.9 Separate root and shoot competition while keeping total soil volume constant

10.10 Ratio of biomass in intraspecific competition for Panicium maximum and Hyparrhenia hirta Outcome of competition of often resource dependant. - The “winner” often the species that can persist at the lowest levels of whatever resource is most limiting

Liebig’s Law of the Minimum: plant growth is limited by the essential nutrient in lowest supply… not by the total nutrient compliment available

Allelopathy vs. other forms of interference Allelopathy is a form of chemical interference. Suppression of one plant, by another, via chemical suppression. There is great variation among the kinds of species, and the particular chemical. Allelopathy seems to have been “invented” evolutionarily many times. One important question is whether the compounds’ primary purposes is this suppression of competitors, or….whether it is a useful side benefit of a compound that does a different job.

Allelopathy has a long, and tortuous, history in ecology. Cornelius Muller published a paper in 1964 focused on shrubs. It made the cover of Science. These shrubs became the essential example of allelopathy- this led to significant recognition for Muller. It was a revolution in the field…. This finding was later challenged, and allelopathy remains a controversial topic. At least, for a while- allelopathy lost favor as an explanation of plant dominance.

In 2004 Ray Callaway published a paper drawing attention to the idea that invasive species may use allelopathy as a “novel weapon” during invasion. I will come back to this.

A closing word on facilitation…

competition