Download The nature of the plant community: a reductionist view

The nature of the plant community: a reductionist view
J. Bastow Wilson
Botany Department, University of Otago, Box 56, Dunedin, New Zealand.
Andrew D.Q. Agnew
Institute of Biological Sciences, University of Wales Aberystwyth, SY23 3DA, U.K.
Contents
Dedication: Frederick E. Clements
Preface
Chapter 1: Plants are strange and wondrous things
1 From plants to communities
1.1 Features of all land plants that predetermine their natural history
1.2 What is a plant community?
2 The accession of species into mixtures
2.1 Step A, speciation: What is a species?
2.2 Step B, Biogeography: The species pool
2.3 Step C, Dispersal
2.4 Step D, Environmental filtering / ecesis
2.5 Step E, Interference filtering (mainly competition)
2.6 Step F, Assembly rules
3 Geographical boundaries
4 Concepts of the space occupied by one species
4.1 The niche
4.2 Guilds
4.3 Guilds and Stratification
5 Conclusion
Chapter 2: Interactions of species within mixtures
1 Introduction
2 Interference: negative effects between plants
2.1 Competition
2.2 Competition and individual ramets
2.3 Factors for which competition occurs
2.4 Plasticity and competition
2.5 Cumulative effects of competition
2.6 Rarity and competitive ability
2.7 Allelopathy
2.8 Parasitism
2.9 Spectral Interference (red/far-red)
2.10 Pest carriers
2 Subvention: positive effects between plants
3.1 Water flow and nutrient redistribution
3.2 Ambient conditions (temperature, evapotranspiration and wind)
3.3 Aerial leakage of nutrients
3.4 Salt
3.5 Shelter from ultra-violet
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3.6 Protection from soil frost-heave
3.7 Hydraulic lift
3.8 ‘Talking trees’
3.9 Subvention conclusion
Litter: the necessary product
4.1 The timing and type of litter production
4.2 Litter decomposition
4.3 Effects of litter
4.4 The direct mechanical effect of litter
4.5 Alteration in environment by litter
4.6 Leachates from litter
4.7 Control by litter of nutrient cycling
4.8 Peat formation
4.9 Can reaction via litter evolve?
Autogenic disturbance: plants as disturbers
5.1 Movement and contact
5.2 Growth thrust
5.3 Crown shyness
5.4 Growth and gravity - tree fall
5.5 Lianas
Plant-plant interactions mediated by other trophic levels
6.1 Below-ground benefaction
6.2 Pollination
6.3 Herbivory
6.4 Indirect impacts of diseases
Interactions
7.1 Litter-herbivore interactions
7.2 Litter-fire interactions
7.3 Litter-herbivore-fire interactions
Conclusion
Chapter 3: Whole-community processes
1 Introduction
2 Allogenic change
3 Directional autogenic succession
3.1 Environmental change
3.2 Pioneer species
3.3 Decrease in biomass
4 Cycling in fact or fiction
5 Switches: the positive feedback processes
5.1 The concept of the switch
5.2 Types of switch
5.3 Outcomes of switches
5.4 Mediating agents
5.5 Switch evolution
5.6 Alternative stable states
5.7 Negative feedback
6 Diversity -> productivity
7 Stability
7.1 Concept
7.2 Reliability (constancy)
7.3 Stability sensu stricto (Liapunovian stability)
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7.4 Resistance to abiotic perturbation
7.5 Resistance to invasion
7.6 Resilience
8 Conclusion
Chapter 4: Mechanisms of co-existence
1 Alpha-niche differentiation
1.1 Resources: type of resource and time of availability
1.2 Heterotroph-imposed niches
1.3 The niche extended by reaction
2 Environmental fluctuation (seasonal, annual and decadal change)
3 Pest pressure (heterotroph challenges)
3.1 Pathogens
3.2 Herbivory, general
3.3 Herbivory of diaspores and seedlings
3.4 Vegetative herbivory
4 Circular competitive networks
5 Allogenic disturbance (disrupting growth, mainly mechanically)
6 Competition/dispersal tradeoff
7 Initial patch composition
8 Cyclic succession: movement of community phases
9 Equal chance: neutrality
10 Inertia
10.1 Temporal inertia
10.2 Spatial inertia (aggregation)
11 Coevolution of similar competitive ability
12 Spatial mass effect (vicinism)
13 Conclusion
Chapter 5: Assembly rules
1 Introduction
2 What rules are we searching for, and how?
2.1 Inductive versus deductive
2.2 Randomisation tests
2.3 Ruling out environmental variation.
2.4 Taxonomic-based limiting similarity
2.5 Process versus pattern
3 Zonation
3.1 Boundaries in zonation
3.2 Fundamental and realised niche
4 Species sorting
4.1 Species associations in succession
4.2 Compositional convergence
4.3 Transitivity in interference networks
5 Richness
6 Limiting similarity
6.1 Limiting similarity in morphological characters
6.2 Limiting similarity in phenology
7 Guild proportionality
7.1 Concept
7.2 Evidence: constancy in space
7.3 Patch models
7.4 Evidence: removal experiments
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7.5 Evidence: successional convergence
7.6 Intrinsic guilds
Texture convergence
Time
Abundance
10.1 Biomass constancy
10.2 Relative abundance distribution (RAD)
10.3 Sparse species
Keystone species
Exotic species as community structure probes
12.1 The nature of exotic species
12.2 Assembly
Conclusion: the Otago Botany Lawn
Chapter 6: Theories
1 Theories
2 Clements and the integrated concept
3 Gleason
4 Whittaker and Austin
5 Hubbell and chance
6 Grime’s CSR theory
6.1 The triangle
6.2 Stress
6.3 Disturbance
6.4 Species/character tests
6.5 Competition
6.6 Community-level tests
6.7 Does succession provide a test of C-S-R
6.8 Conclusions
7 Centrifugal theory (Keddy)
8 Tilman’s theory
8.1 Co-existence
8.2 Species diversity
8.3 Succession
8.4 Intensity of competition
8.5 The competitive process: R*
9 Grime versus Tilman
9.1 Strategy
9.2 Competition
10 Synthesis
Glossary
References
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Preface
We have written this book because we like being in plant communities and we like trying to
find out how they work. Books exist describing the plant communities of parts of the world, or the
whole of it. Other books assume that there are rules governing the assembly of communities. We
hope to examine plant communities in general terms, but without preconceptions about them. The
term ‘reductionist’ means that we start with the basic features of plants, and do not believe the more
complex ones without good evidence. The book is deliberately unbalanced. We have provided a
broad overview, and then concentrated on particular areas that we feel have been done less than
justice in the literature, or where we feel we have a particular contribution. These include
environmental reaction, autogenic disturbances, switches (sensu Howard Odum) and assembly
rules.
We have provided a glossary limited to terms that will be less familiar, or have been used in
different ways in the literature.
The overall conclusions have been the most difficult. Our argument from first principles has
not led us to an overarching theory, but then the closest anyone has come to this is F.E. Clements,
to whom we dedicate this book. He saw much and understood much, but HIS conclusions were
mainly descriptive rather than predictive. There is only one recent realistic and comprehensive
theory, and the real world turns out to be too complex for it to be more than a guide. At present
community ecologists can only see through a glass darkly.
We are very grateful to those who have read parts or all of drafts: Gretchen Brownstein,
Amadou S. Camara, David R Causton, Arthur O. Chater, Peter Chesson, Robert M.M. Crawford,
Tony D. Fox, Gareth W. Griffiths, Ruth F. Griffiths, Richard Hartnup, Janice Martin, John Baron
Steel, Lizzie Wilberforce. We thank Raewyn Stedman for support.
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The nature of the plant community: a reductionist view
J. Bastow Wilson
Botany Department, University of Otago, Box 56, Dunedin, New Zealand.
Andrew D.Q. Agnew
Institute of Biological Sciences, University of Wales Aberystwyth, SY23 3DA, U.K.
Glossary
Allee effect: Population growth rate is low in sparse populations, probably due to difficulty in
contacting a mate but possibly due to problems in attracting a disperser.
Alpha (niche / guild): Using particular resources, i.e. different resources from other species in the
local community at a point.
Alterative stable states (ASS): Two or more vegetation/environment states in the same underlying
habitat, each state locally stable but able to be shifted to another state by a large perturbation.
Apomixis: The production of a seed by a plant without meiosis or gamete fusion, therefore
potentially identical in genotype to the mother plant. Babies without sex.
ASS: Alternative stable states.
Barro Colorado Island: An 1,500 ha island formed when a valley in Panama was dammed to form
part of the Panama Canal. It has been used as an example of an area of mainland converted
into island status. Numerous ecological studies have been conducted there. The establishment
of permanent plots for tree demography by Stephen Hubbell and Robin Foster in 1982 is
particularly important.
BCI: Barro Colorado Island.: change in text
Benefaction: A reaction by one species that increases the survival/growth/reproduction of another.
Beta (niche / guild): Tolerant of particular environmental (non-resource) conditions within
particular spatial range(s), i.e. differing in tolerances and therefore spatial distribution from
other species.
BioDepth: A collaborative, multi-site research programme funded European Community, into the
effects of species richness on yield, invasion resistance, etc. A triumph of moulding good
ecological research to the political agenda of the funding agency
C: Carbon.
C: In C-S-R theory, C habitats are ones where productivity is high and disturbance low, so that
competition is intense, and C species are strong competitors able to persist in the vegetation
of such sites. These concepts depend on the theory’s suggestion that competition is more
intense in more productive sites.
Cedar Creek: Cedar Creek Natural History Area, an experimental field area comprising oldfields,
belonging to the University of Minnesota, and the site of many experiments by David Tilman
and others.
Challenge: a test by an organism of a new habitat.
Competition: An interaction between individuals, brought about by a shared requirement for a
resource in limited supply, leading to a reduction in the survivorship, growth and/or
reproduction of at least some of the competing individuals concerned.
C-S-R: The theory of J.P. Grime that habits and species can be arranged in a triangle, comprising a
tradeoff between competition (C), stress (S) and disturbance/ruderality (R).
CWD: Coarse woody debris, i.e. litter of branches and whole trees.
Disseminule: A sexually or asexually produced dispersal unit capable of developing into a new
individual or ramet.
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Disturbance: A marked change in the environment for a limited period, often with the removal of
plant material.
Ecesis: The post-germination survival, growth and establishment of a plant in a habitat.
Embryophyte: Any plant from liverworts ‘upwards’, i.e. bryophyte, pteridophyte, gymnosperm or
angiosperm.
Facilitation: A reaction by one species that increases the survival/growth/reproduction of another
but is disadvantageous to the plant causing the reaction.
Genet: A genetic individual, i.e. the derivative of one zygote. It may be one recognizable
‘individual’, or it may comprise many plants produced by vegetative reproduction or by
apomixis.
Getafix: The magician in the Asterix books who can work any wonder by the right magic potion.
Guild: A group of species that are similar in some way that is ecologically relevant, or might be.
Interference: This covers competition, allelopathy, parasitism, pest transmission, and other
interactions in which the primary effect is negative of one plant on another.
Leaf: “Although no satisfactory definition of a leaf is possible, I shall assume that we all know
what we are talking about”: F.G. Gregory, cited by L. Croizat in his ‘Principia Botanica’.
Liapunov stability: The ability of a community, after an infinitely small pulse perturbation, to
return to its original state in infinite time (assuming external factors and the species pool
remain constant).
Macrophyte: Macroscopic plant, e.g. tree.
Mutualism: An interaction between two plants that increases the survival/growth/reproduction of
both.
Mycorrhiza (pl. mycorrhizae): A close association between a fungus and a root. The two major
types, found in hosts from many families, are endotrophic and VAM. Other types are
associated with the Ericales (heaths etc.) and Orchidaceae (orchids).
N: Nitrogen, generally as nitrate or ammonium salts.
Niche: A region in n-dimensional hyperspace” where the dimensions are all the environmental,
resource or behavioural (e.g. phenology, foraging) parameters that permit an organism to live.
NZ: New Zealand.
P: Phosphorus, generally as phosphate.
Park Grass: The world’s longest-running ecological experiment and therefore most important.
Established at Rothamsted Agricultural Station, in the English midlands in 1856. There were
originally 20 plots with different fertiliser treatments, though most have been subdivided
since. They have been monitored, with varying degrees of detail, ever since.
Plant: A photosynthetic organism with chlorophyll a, or a close saprophytic or parasitic relative.
Press perturbation: A change in the physical or biotic environment of a community that continues
to be applied.
Pulse perturbation: A change in the physical or biotic environment of a community that is applied
and immediately removed (as immediately as it can be).
Quadrat: A vegetation sample of specified shape and area or volume.
R: In C-S-R theory, R habitats are ones where there is frequent disturbance, i.e. removal of plant
material, and R species are the ruderals typical of such habitats. They are similar to ‘r’ species
of r-K theory.
Ramet: A vegetatively-produced plant unit, such as a strawberry ‘plant’.
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Reaction: The change in local environment caused directly by a plant. ‘Ecological engineering’ is
similar, but perhaps has implications that the change benefits the species/community,
comprising a switch. ‘Niche construction’ seems to be a synonym, with ‘positive niche
construction’ causing a switch and ‘negative niche construction’ comprising facilitation.
Relay floristics: A caricature of F.E. Clements’ concepts of succession, in which vegetation must
pass through a relay of seral stages, each stage facilitating the next, ending in the climax.
Reliability: Lack of temporal variation in a community.
Resilience: The degree and speed of recovery of a community after a pulse perturbation.
Resistance: Lack of change in a community when a pulse perturbation is applied.
RGR: Relative growth rate = growth per unit time per unit biomass. It is equivalent to the r of
zoological population models.
RGRmax: RGR, at the phase of growth when RGR is highest for the species (young) in
environmental conditions that produce the highest RGR in that species (which is hard to
achieve in practice).
S: In C-S-R theory, S habitats are ones where productivity is low, and S species are ones typical of
such habitats.
SLW: Specific leaf weight = leaf weight per unit area, e.g. cm2 / g. It is the reciprocal of SLA =
specific leaf area, and references to SLA have been converted to SLW for uniformity.
Species diversity: Species richness and the evenness of abundance among species in an area (e.g.
quadrat) of specified size and shape. With the right combination of indices, diversity =
richness × evenness.
Species richness: The number of (plant) species present in an area (e.g. quadrat) of specified size
and shape.
Stability: see Liapunov stability.
Stratum (pl. strata): A vertical layer, usually in an aboveground plant canopy but also belowground.
Subvention: A positive interaction between plants, including benefaction, facilitation and
mutualism.
Switch: A positive feedback between a species or community and its environment, in which the
species/community changes the environment by reaction in a way that gives it relative benefit
over alternative species/communities.
Synusia (pl. synusiae): A stratum or other vertical rôle in a forest such as an epiphyte, aerial partial
parasite or liana.
University of Otago Botany Lawn: Established c. 1965 with the sowing of an Agrostis capillaris /
Festuca rubra mix. Thirty six other species arrived since through natural dispersal. Since
1965 the lawn has been mown to a height of c. 2.7 cm, fortnightly in the growing season and
monthly in winter.
USA: United States of America, a renegade British colony.
VAM: Vesicular-arbuscular mycorrhiza. The type of fungus-root association in which the fungal
hyphae are extensive within the root, and indeed form arbuscules within the root cell. It is
also called endotrophic.
Vascular plant: Pteridophyte, gymnosperm or angiosperm.
Xylem: The water-conducting tissue of a vascular plant. It comprises the ‘wood’ of trees.