Weed Life History and Agricultural Community Assembly

A.  Plant invasion: dipersal, colonization and enduring occupation
B.  The genetic-reproductive colonization of agricultural opportunity space
C.  The phenotype-trait colonization of agricultural opportunity space
D.  The life history of weed colonization
E.  Change in the structure of plant communities

Trait basis of the invasion process.  Why study the invasion process in terms of traits?  They are identifiable phenotypes, functions and structures.  The are selectable and heritable.  How should these critical traits best be seen: in isolation or in a broader context?   Life history provides some important advantages to organizing invasibility traits:
•"Timing is Everything": when a plant performs important developmental processes and activities, relative to its neighbors, it a key to its success in the invasion process;
•If a particular invading plant is at the right place at the right time, it is the traits that it expresses at those times that make it a winner or a loser over its neighbor.
•Trade-offs among these traits that compete within the individual phenotype are apparent when we organize them into similar times in their life history.

Phenotypic life history traits.  Given an opportunity in a locality, the second condition necessary for plant invasion is the presence of propagules of a particular species possessing life history traits suitable to exploit that space.  A life history perspective provides some advantages in understanding how invasion occurs in a community.  Plants experience the same general life history processes (birth, dispersal, recruitment, vegetative and seed reproductive growth).  This life cycle can be described by the underlying plant morphological structures, developmental processes and whole plant activities that occur during each of these phases (Table 2).  The time a plant performs these developmental processes and activities, relative to that of its neighbors, determines its success in the invasion process: timing is everything.  If a particular invading plant is at the right place, at the right time, it is the traits that it expresses at those times that make it a winner or a loser relative to its neighbor.   A plant's life cycle is a Markov Chain process in which the state of the plant at any one time is a direct consequence of its state in the previous time period (Dekker, 2004a).  Failure at any time in the life history ends the invasion process.

Plant morphology, development and activity during life history.  The table below summarizes the plant morphological structures, developmental (physiological, morphogenic) processes and whole plant phenotypic activities that occur during the plant life history processes of birth, dispersal, recruitment, vegetative growth and seed reproductive growth.  

Weed Archetypes presents information on specific, archetypical, weeds that display much of the diversity in life history traits found among individual weed species.  The life history of weeds and invasive plants can be viewed from several organizing perspectives:
    •Taxonomy-Phylogeny:  dicotyledenous-graminaceous-other (e.g. sedges)
    •Life Cycle:  annual-biennial-perennial
    •Mating system and Propagule Type also provide insights into life history

Life history model diagram (Andy Heggenstaller, 3.2.04)
Annual, perennial and biennial weed species follow part or all of this sequence of developmental events.

©jdekker-2005