The nature of the plant community:

a reductionist view

A discussion of J. Bastow Wilson’s book, Chapter I

Dane Kuppinger and Amanda Senft

I. From Plants to communities

• Landforms of the Earth result from an underlying geological diversity, moulded by geomorphological forces and mostly clothes in vegetation.

• Plant ecology has taken 3 approaches– Descriptive– Reductionist, without generalities attempted– Theoretical, decuctive of empirical

• This book, “an attempt to move reality and theories closer.”

The problem with theories to date

• Some trivial, none have reliable truth

“The only reason students put up with this ‘science’ is that they, like us, find being in the

field more pleasant than being in the lab”

• Q: Are plant ecology theories this unreliable?• Q: How good a job does this book do in terms

of deriving theories with “reliable truths”?

Features of land plants• Root in the soil → Sedentary• Sedentary behavior puts premium on structure

and chemistry defenses → Discarded modules• Germ cells defined just before meiosis →

Somatic mutations passed on• Animals move but stay in same body, Plants are

sedentary, but must replace organs and elements → Plants move, animals don’t

• Q: Is this view helpful or just confusing?

The problem of the individual

• “The animal concept of ‘individual’ is not appropriate or useful in plants.”

• How to deal with vegetative reproduction?

• Do somatic mutations make ‘individual’ plants “a colony of apical meristems, or apical meristem segments”?

What is a plant community?

“He accepts “plant species mixtures encountered in the field”, but is “not persuaded of the relevance of

conceptual communities.”

“Naturally generated plant stands where the environment of the individuals of one species

potentially , predictable and persistently includes individuals of its own and usually a restricted

number of other species.”• Q: Is this acceptable as a good/useful definition? • Q: Does it leave anything out?

Accession of species into mixtures

• A. Speciation• B. Biogeography• C. Dispersal• D. Environmental

filtering• E. Productivity and

biotic filtering• F. Assembly Rules

Fig. 1.2: Pathways from the species pool to community entry.

Species pool(metacommunity)

Dispersal

Challenge

Niche unavailableNo entry!

Niche available

Niche constructed

PopulationEstablishment

Steps of species accession

• Spp. pools: – Confounding Q is whether the pool is defined

before or after interference (competition).

• Q: What is his definition of a species pool?• Dispersal:

– Dispersal is usually leptokurtic often best fit by a negative exponential function.

Invasion

• “In general, the number of disseminules arriving (the propagule pressure) will not matter; a smaller number will delay an invasion, but not prevent it.”

• “[Productivity and disturbance] affect the rate of invasion more than the eventual fate of invasion”

• Higher competition → increased difficulty for additional spp. to establish

• Q: Do we accept the proposed invasion controls?• Q: Does ↑ competition affect the outcome or just

the rate of invasion?

Geographic Boundaries: Two types

• Gradual: species become patchier, individuals are smaller, less successful, less genetically diverse, and more sensitive to disturbance

• Abrupt: characterized by a sharp edge, constant fecundity

• Q: What are some things that would limit a species’ range and what pattern would you expect at each?

Red Spruce USDA FS, 1984

Niche Theory

• Niche as a species attribute (Grinnell, Hutchinson, etc.):

• Niche as ecological space: Empty niches

• Fundamental vs. Realized Niche

• Alpha vs. Beta Niche

– Beta niche: the range of physical environmental conditions under which the fitness of a species is maintained

– Alpha niche: represents the resources used within a community/site

• Q: Which niche definition is helpful in what situation?

Alpha vs. Beta

• Alpha Niche– Morphology – Growth phenology – Chemical functioning– Plant/plant

interactions

– Exclusion of species with the same alpha niche

• Beta Niche– Climate – Soil– Geomorphology– Other Organisms

– Co-occurance of species with same beta niche

Guilds

• “A group of species that are similar in some way that is ecologically relevant, or might be “

• Or: “a group of species that occupy similar niches”

• Alpha and beta guilds

• Q: Are beta guilds communities?

Stratification: Alpha guilds