Dekker, J. 2011. Evolutionary ecology of weeds
A weed science textbook. A new weed science textbook is now available. This book provides a unique, alternate perspective to weed biology and is the content for Agronomy 417/517, Evolutionary Ecology of Weeds. The content and structure of this book arose in Agronomy 517, taught since 1991. It is therefore the fruit that was cultivated and harvested by the many students who discussed and contributed to its development as they learned.
A biological explanation. This book is an explanation of the ecology and evolutionary biology of weeds and other colonizing and invasive plants. Weed biology is the ecology and evolution of plants in localities influenced by human activity, notably agriculture. The focus is on these big WHY, HOW & WHAT questions of weed biology:
What are weeds?
Why do we have weeds?
Why do we have the weed species that we do? (And not others)
Why do these weeds look and behave as they do?
How did the weeds we have get to be the way they are?
What is the basis of future changes in weeds?
The goal of this book is to provide comprehensive explanations of factual information about weed biology in an evolutionary context as the basis for understanding and management of local weed communities of the future. The goal is also to provide the reader with a dynamic framework to guide understanding of new observations in the future: a mental 'toolkit' to focus observations of new weed phenomena, a way to understand the fundamental forces in nature that cause weediness.
Nothing in biology makes sense unless seen in the light of evolution (Dobzhansky, 1973). Weed and crop management is the management of selection and elimination leading inexorably to the weed adaptations that plague our fields and interfere with our crops. To understand what we observe in agriculture and want to manage more wisely and efficiently, we need to understand how the evolutionary process works in weed communities.
Seizing and exploiting opportunity. The thesis of this book is that human disturbance (e.g. tillage, herbicides, atmospheric pollution, frozen winter) creates opportunity spacetime by leaving unused resources (nitrogen, water, light) in a local field with few or no plant neighbors. Opportunity spacetime is seized and exploited by heterogeneous plant phenotypes with preadapted life history traits expressed at favorable times as the growing season unfolds. Successful weed populations assemble and interact with crop and other weedy neighbors in their particular locality. The consequences of successful interactions lead to local adaptation maximizing survival and fitness in that plant community.
Table of contents and course syllabus
UNIT 1: THE NATURE OF WEEDS
1 The nature of weeds
Topics: What is a weed? Weeds and human nature. Weedy traits. The origins of weeds and crop domestication. Wild-crop-weed complexes. World crop-weed species groups.
UNIT 2: THE EVOLUTION OF WEED
2 Evolution, natural selection and weedy adaptation
Topics: Evolution. Natural selection and the process of natural selection. Adaptation.
3 Formation of the local weed population: Precondition to natural selection
Topics: Weedy opportunity, weedy habitats, and niches in the local community. Habitat heterogeneity and dynamics. Limiting resources and pervasive conditions in local opportunity. The nature of plant invasions of local opportunity.
4 Generation of genotypic and phenotypic variation: First process of natural selection
Topics: Genotypes and phenotypes. Generate genetic and phenotypic variation. Phenotypic plasticity and somatic polymorphism
5 Survival, reproduction and inheritance: Second process of natural selection
Topics: Survive, avoid mortality. Reproduce the fittest, eliminate the others. Inheritance: transmit parental traits to offspring. Mating systems and inheritance.
UNIT 3: ADAPTATION IN WEED LIFE
7 Reproductive adaptation
6 Weed life history
Topics: Phenotypic life history traits. Plant life history classification systems. Ecological demography of plant population life history dynamics. Evolutionary, trait-based, weed life history population dynamics.
Topics: Flowering, anthesis, fertilization and birth. Embryo adaptation: embryogenesis and dormancy. Evolutionary ecology of seed heteroblasty. Observable seed dormancy-germinability regulation life forms. Propagule adaptation: post-abscission fecundity.
8 Propagule dispersal in space and time
Topics: The evolutionary ecology of dispersal structures. Dispersal in space. Dispersal in time: formation of seed pools in the soil. Propagule germination and recruitment.
7 Reproductive adaptation
UNIT 4: ADAPTATION IN LOCAL PLANT
Weed-crop communities as complex adaptive systems
9 Neighbor interactions in local plant communities
Topics: Adaptation to neighbors in the community. The nature of neighbor interactions in the community. Strategic roles and traits of interference and facilitation with neighbors. Effects of neighborhood interactions on plant density, growth and form.
10 Weed community structure, dynamics and biodiversity
Topics: Weed communities. Weed community structure: genotype structuring. Exploiting opportunity: weed community dynamics. Ecological roles-guilds-trades in weed-crop plant communities. Changes in plant community structure. Weed community biodiversity.
This new weed science book provides a unique, alternate perspective to weed biology. A small sample of some of the new concepts in this book include:
1: What a weed is: sustainable membership in a
The top 79 weed-crop species-groups (e.g. Amaranthus, Brassica, Chenopodium, Panicum, Setaria, Trifolium, Solanum)
2: Evolution never rests:
Cropping systems cause local weed success
3: The process and steps of plant invasion:
What weeds want: the nature and structure of cropping system opportunity
Chapter 4: The extended phenotype: Weeds-R-Us
5: Weed mating systems:
Heterogeneous, promiscuous sexual mating systems anticipate every cropping system change
Chapter 6: Timing life history trait expression to seize and exploit cropping system opportunity
7: Hidden blueprint after layby:
When seed dormancy is induced to time future weed infestations
8: Waiting for the right moment to strike:
Formation of agricultural soil seed pools
The right moment to attack: weed seed recruitment patterns ruthlessly track cropping tactics
9: Weed-crop communities as complex adaptive
Emergent behaviors are unpredictable
Weed-crop neighbor interactions:
Is facilitation more important than competition?
Strategic roles of adaptive traits in interference and facilitation
Ecological roles in weed-crop communities
Ready for anything: weed population shifts
Weed biodiversity and the myth of the biotic resistance hypothesis
Evolutionary Ecology of Weeds is a textbook available free on the internet as a downloadable .pdf file until publication (2013). Textbook URL:
Agronomy 417 and 517, Evolutionary ecology of weeds, is offered every Spring semester at ISU to advanced undergraduate and graduate students as both an on-campus and distance education course in a unified classroom. Course URL: