Lesson 3: Species in the environmental
complex
• Environmental factors and plant
distribution
– Liebigs law of the minimum
– Shelfords law of tolerance
– Billings Holocoenotic concept
• Ecotypic variation within species:
– Morphological variation
– Ecophysiological variation
– Genetic variation
Why are organisms absent some
places and abundant in others?
Why are organisms absent some places and
abundant in others?
•
Abiotic Forces: plants have certain limits regarding environmental
tolerances.
–Temperature, moisture, sunlight, pH, substratum, salinity, atmosphere, etc
•
Biotic Forces: Organisms compete for space and resources, and some eat
others.
–Competition, predation, symbiosis, nest sites, habitat modification.
•
Opportunity (history): organisms are absent where there is no geographical
access.
–Sometimes when they are introduced into areas where they were previously
absent, havoc ensues.
–introduced (exotic) species are the second most important cause of extinction.
Habit destruction is the first.
–Examples: kudzu, fire ants, killer bees, zebra mussels, Asiatic clams, Japanese
honeysuckle, water hyacinth, Hydrilla, Egeria, Japanese beetles, honeybee mites,
giant slugs, Brazilian pepper, tamarisk, thistles, Australian pine, privet.
Justis Liebig (1803-1873)
Liebig’s Lab in Giessen, 1840
Liebigs Law of the Minimum
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Liebig recognized that plant growth is controlled by plant
nutrients, and whichever nutrient is in most limited supply
controls the plants growth.
This concept was later expanded to cover other environmental
factors such as water, light, temperature.
He noted that plants had varying ranges of tolerance for a given
factor.
• “The growth or distribution of a plant is
dependent on the one environmental factor most
critically in demand.”
Shelfords Law of Tolerance
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Shelford in 1913 noted a weakness in Liebigs general law
which came to be known as the Law of Tolerance. And this
in turn was modified by Ronald Good, a plant geographer:
“Each and every plant species is able to exist and
reproduce successfully only within a definite range of
environmental conditions.
Good rated climatic factors above edaphic factors.
Some Examples:
– Salinity tolerance in plants (intertidal zonation)
– Thermal constraints on activity (sparrow microclimates,
shown in the diagram from Smiths Ecology and Field
Ecology.)
Shelfords
Law of
Tolerance
•
From Smith’s Ecology and Field Ecology.
The distribution of
a species along an
environmental
gradient generally
approximates a
Gausian
distribution, with
the optimal
occurrence
somewhere near
the midpoint of the
distribution.
Steno- and Eury•
•
These prefixes describe the width of the ecological niche in
relation to a given environmental factor.
For example, A plant with a narrow range of tolerance for
temperature is termed stenothermic. Plants with a wide
thermal tolerance are termed eurythermic.
-phile and -phobe
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These suffixes are used to describe plants that favor one
extreme of an environmental gradient.
For example, a plant favoring snowy habitats is called a
chionophile, and a plant that grows only in windblown,
snowfree habitats would be called a chionophobe.
Plants operate within the tolerance limits for all the
critical factors for their growth
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•
Add Fig. 3-1 (BBPGS)
No single factor
controls the
distribution of a
plant.
• Good thought that
climate factors were
most important
controls, edaphic
(soil) factors were
next most important,
and biotic factors,
such as competition,
were least important.
Biotic Controls: Competitive exclusion in animals:
Gauses experiment using protozoans (Paramecium)
•
.Competition with other species can strongly influence how
a species will respond to an environmental factor.
•
The concept of what defines a species niche is one of the
most hotly disputed topics in ecology. This famous
experiment by the Russian biologist G.F. Gause (1934) first
demonstrated the principal of “one species, one niche”. He
did the experiment using small animals.
Biotic Controls: Competitive exclusion in animals:
Gauses experiment using protozoans
(Paramecium)
•
P. aurelia
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P. caudata
Grown separately
Grown together
Based on Gause 1934
In separate but identical
bacterial cultures. Each
species showed a similar
growth rate in the
absence of competition.
When placed together, P.
aurelia was able to
compete successfully for
the bacterial food, and
eventually eliminated P.
caudata.
In another experiment P.
caudata was grown with
P. bursaria. Both species
fed on the bacteria, but
in this case, P. bursaria
fed on the bacteria at the
bottom of the tub, while
P. caudata fed on the
bacteria in suspension-Coeexistance because of
different niches.
Competitive exclustion in plants: Harpers
experiment using duckweed (Lemma)
Adapted from Harper 1961
Effects of competition:
shift of ecological optimum
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Ellenberg showed that the growth of two
species of mustard have very similar
response to pH when grown separately.
•
When grown together in mixed culture,
they both shift their optimum pH a bit.
Spergula favors a lower pH, and
Raphanus favors a higher pH.
•
In most cases it is unlikely that they will
have exactly the same niche, where one
totally excludes the other.
Solid line: Spergula arvensis (Spurry)
Dashed line: Raphanus raphanistrum (a wild mustrard)
From Ellenberg 1958
The ecological (or realized) niche for a species may shift or be truncated in the
presence of competition.
•
Add Fig. 3-3 (BBPGS)
Another view of fundamental vs. realized niches
From Smith 1977
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The presence of other species in portions of the range of characteristics, can eliminate
Species A from parts of its fundamental niche, so that its realized niche is smaller.
Dwight Billings
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Dwight Billings helped to
crystallize the study of the
relationship of plants to the
environment. He was one of
the major proponents of
using an ecophysiological
approach.
•
He believed that the best way
to study these relationshps
was through detailed
autecological studies of plant
species and how they react to
changes in their environment.
Why do plants grow where they do?
The holocoenotic
environmental
complex
W.D. Billings, 1952. The environmental complex in relation to plant growth and
distribution. Quaterly Review of Biology 27: 251-265.
•
A complex, indvisible
whole system
consisting of the plant
and its multitude of
environmental
influences.
•
Holocoenosis =
ecosystem?
•
Compare to Tansleys
concept of the
“ecosystem”, which
also included time and
change.
•
Billings concept is
therefore an
ecosystem at a
moment in time.
Billings: Groups of factors in a terrestrial plant environment:
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Climate
Edaphic
Geographic
Topographic
Pyric
Biotic
Groups were subdivided into: factors subfactors and aspects.
Examples:
Climate was divided into the factors Radiation, Temperature, Water, Atmospheric gases.
Edaphic was divided into Parent material, Soil;
Geographic was divided into Gravity, Rotational Effects, Geographic Position,
Vulcanism, Ditrophism (folding, faulting), Erosion and Deposition, Topography, etc.
The factor Radiation was divided into the subfactors: Solar radiation, cosmic radiation, and
terrestrial radiation.
The subfactor Solar radiation was subdivided in the aspects, wavelenths, intensity,
photoperiod and other cycles.
Billings identified a total of 64 environmental aspects, but this was by no means a
comprehensive list. It only served to illustrate how complex the plant environment is and
how the aspects interact among themselves and the plant.
Some conclusions from Billings paper: Factors of a terrestrial plant
environment:
• Environment of a plant is holocoenotic (forms a complete system in
combination with the plant).
• For a given species, limiting factors can be different in different parts of
its range.
• The total environment is dynamic and varies both space and time.
• Vegetation can be used as an indicator of the total environment if the
tolerances of its characteristic species are known.
What is a species?:
The biological species concept
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A group of natural populations that are morphologically, genetically, and
ecologically similar.
– This definition involves
• Appearance (morphology)
• Breeding behavior (genetics)
• Habitat distinctiveness (ecology)
•
They may or may not be interbreeding, but they are reproductively isolated
from other species.
The biological species concept
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Classical taxonomists have focused most on morphology. This
approach has been until recently the only tool to determine the
relationship of one species to others.
•
Newer approaches to the species focus on the genetic aspects -how population of plants maintain their distinctiveness through
genetic isolation.
•
These isolating barriers may be due to:
– breeding behavior (time of flowering, type of pollinator),
– habitat, or geographic isolation, or
– inability to form fertile hybrids.
Ecotype Concept
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Many botanists have noted that within a given species there is often
considerable morphological, physiological, or phenological variation.
•
Kerner in Switzerland noted such variation but thought that the various
traits were plastic responses to environmental factors.
•
In the 1920s Göte Turesson confirmed that many of the traits were
heritable. He collected samples of populations of many plant species from
all over Europe and grew them in a common garden in Sweden. He noted
considerable variation in a variety of factors within a given species even
though the various populations were fully interbreeding.
Göte Turreson: Ecotype Concept
Table 3-2. From Barbour et al. 1999.
•
Turreson grew
plants of the same
species from all
over Europe in his
transplant garden
in Åjarp, Sweden.
•
He noted within
one species of
hawkweed
collected from
woodlands, fields,
and dunes, there
was consistent
variation in leaf
morphology,
pubescence, and
autumn dormancy.
Turresons observations of Betula
.
ALPINE TUNDRA
MID-ELEVATION
FOREST
COASTAL BLUFFS
LOW TEMP (SPRING)
MOD TEMP (SUMMER)
MOD. TEMP (SUMMER)
PROSTRATE
TINY LEAVES
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TREE
LARGE LEAVES
SHRUB
FLESHY LEAVES
THESE DIFFERENCES PERSISTED IN THE COMMON ENVIRONMENT GARDEN LEADING
GOTE TURESSON TO LABEL EACH POPULATION AN ECOTYPE OF ITS SPECIES
Key aspects of ecotypes according to Turresons concept
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Wide-ranging species are differentiated into different hereditary groups
that are genetically based (ecotypes). They are discrete entities with clear
differences separating them from other ecotypes.
•
The genetic differences are adaptations to the different habitats.
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Ecotypes occur in distinctive habitats. In a given habitat populations of
different species often exhibit similar morphological and developmental
characteristics. Distinctiveness can be morphological, physiological,
and/or phenological. (e.g. (1) life form, (2) timing of growth, (3) tolerance of
frost, (4) tolerance of salt, and (5) tolerance of shade.)
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They are potentially interfertile with other ecotypes of the same species.
Clausen, Keck, and Heisey (1940)
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Fig. 3.5. Barbour et al. 1999.
Ecotypes along an elevation transect in
California.
Initially, they had many transplant gardens
located along this transect and were
transplanting about 180 species from
different areas into as many gardens as
possible.
Reduced the number of gardens to the three
at Stanford, Mather, and a Timberlilne site,
and 60 species.
Transplanted local species from each site
into the other gardens.
Summary of environmental conditions at the transplant
gardens
Table 3.3. Barbour et al. 1999.
Three ecotypes (subspecies) of Potentilla glandulosa and their appearance in
each of the transplant gardens
Ecotype
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Photos along the diagonal
show the species as it
grows at its native site.
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All of the populations were
shown to be interfertile.
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They concluded, as
Turesson did, that species
are really composed of
genetically distinct groups
of ecotypes which are best
suited their specific
environment.
Nevadensis
reflexa
typica
Fig. 3-6 from Barbour et al.
Mooney and Billings (1959): Ecophysiological variation in
ecotypes of Oxyria digyna (Mountain sorrel)
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Took the concept
one step further
with detailed
examination of the
physiological
responses of
different
population.
Morphological, biochemical, and phenological differences between the arctic
and alpine populations of O. digyna
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Insert Table 3-6 from BBPGS
Physiological response of O. digyna ecotypes: Photosynthetic response
Temperature varies
Light intensity varies
Fig. 3-8, Barbour et al. 1999
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CO2 uptake of two ecotypes at different
temperature and light conditions.
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The alpine plants had higher
photosynthetic response to both
temperature and light, reflecting the
generally warmer and sunnier conditions
in the alpine environment.
•
The optimum point was also higher in
each case for the alpine plants (i.e.,
higher light intensity and higher
temperature.
•
Ecophysiological differences have now
been documented at much more local
scales, between geographically close
populations, consistent with idea of
ecoclines.
Ecocline concept
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Langlet (1959) examined the growth of Pinus sylvestris at
580(!) sites in Sweden and concluded that species really
formed a cline, or continuum of variation.
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Quinn (1987) showed that every population of Danthonia
caespitosa had distinctive growth characteristics
(phenology, morphology, physiology). He concluded that
each population was in some sense individualistic.
McNaughton (1966): enzymatic connection in Typha
latifolia
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http://plants.usda.gov/
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Fig. 3-9 , Barbour et al. 1999
Another step closer to the
demonstrating actual genetic
control for ecotypic variation
of physiological differences.
Point Reyes: foggy coastal
site.
Red Bluff: hot Sacramento
Valley.
Collected dormant rhizomes
from each site and placed in
common greenhouse.
Made plant extracts and
collected 3 enzymes.
Subjected to the enzymes to
heat stress of 50 ˚C for up to
30 min.
One of the critical enzymes
(malate deydrogenase) from
Red Bluff showed much
higher activity with higher
temperature.
Other studies the helped demonstrate differences in ecotypes at the
genetic level
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Smith and Pham (1996) using molecular biology showed high genetic
variation in separate populations of wild onion.
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McCauley et al. (1996) examined spatial patterns of chloroplast DNA in
Silene alba, and found the most similar genotypes were those in close
proximity to each other.
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Rejmanek (1996) found major differences in the amount of nuclear DNA in
different pine species. Aggressive invaders of pines had small amounts of
nuclear DNA, which correlated with a shorter time for cell division, more
rapid growth.
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Techniques of molecular biology have now been used to identify
differences in specific genes.
Rapid evolution of heavy metal tolerance in
bent grass (Danthonia tenuis). Anthony
Bradshaw and students (1996):
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Studied mines in Wales abandoned about 100 yr
ago, and contaminated with high levels of Cu,
Fe, Zn, and Pb. Heavy metals cause proteins to
precipitate leading to death.
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Bent grass was one of the few species growing
on mines and away from mines.
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Bradshaw grew plants in concentrations of 20
and 2000 ppm of heavy metals. Plants on the
mine sites grew in both solutions, but plants on
other sites grew only in 20 ppm solution.
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Tolerance is present in 0.3% of natural
population but is strongly selected for on the
mine sites.
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Plants with the tolerance make specific proteins
to bind the heavy metals, and this takes energy
away from growth of leaves and roots, making
these plants less competitive in natural
populations.
http://www.planning.sa.gov.au/
See: 1. Bradshaw, A.D. and McNeilly, T.
1996. Evolution and pollution. London:
Edward Arnold.
2. Salt, D.E. et al. 1995. Bio/Technology
13: 468-474.
3. Adler, T. Science News. 1996. 150:4243.
McGraw and Antonovics study of Dryas octopetala
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Examined the causes of ecotypic variation in ssp. octopetala and
ssp. alaskana
An integrated approach to study plant populations using:
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Growth chamber studies
Field transplants
Competition trials
Pollination ecology
Photosynthesis measurements
Determination of photosynthate allocation patterns in plant organs
McGraw, J.B. 1985b. Experimental ecology of Dryas octopetala ecotypes. III.
Environmental factors and plant growth. Arctic and Alpine Research, 17: 229239.
Summary
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Environmental factors and plant distribution
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Liebigs (1840) law of the minimum
Shelfords (1913) law of tolerance
Holocoenotic concept of the the plant environment (Billings 1952)
Ecotypic variation within species:
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Morphological variation (Turesson 1920s, Clausen, Keck and Heisey 1940,
Langlet 1959, Quinn 1987)
Ecophysiological variation (Mooney and Billings 1961, McNaughton 1967;
Björkman 1968)
Genetic linkage identified (e.g., Rejmanek 1995)
Rapid selection for genes and adaptation to highly toxic environments
(Bradshaw and students)
Literature for Lesson 3
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Billings, W.D. 1952. The environmental complex in relation to plant growth and
distribution. Quarterly Review of Biology 27: 251-265.
Björkman, O. 1968. Carboxydismutase activity in shade-adapted species of higher
plants. Physiologia Plantarum 21:1-10.
*McGraw, J.B. and J. Antonovics. 1983. Experimental ecology of Dryas octopetala
ecotypes. Ecotypic differentiation and life-cyle stages of selection. J. Ecol.: 879-897.
*McGraw, J.B. 1985b. Experimental ecology of Dryas octopetala ecotypes. III.
Enviornmental factors and plant growth. Arctic and Alpine Research, 17: 229-239.
McNaughton, S. J. 1966. Thermal inactivation properties of enzymes from Typha
latifolia L. ecotypes. Plant Physiology 41: 1736-1738.
*Mooney, H.A. and W.D. Billings. 1961. Comparative physiological ecology of arctic
and alpine populations of Oxyria digyna. Ecological Monographs 31: 1-29.
Rejmanek, M. 1996. A theory of seed plant invasiveness: the first sketch. Biological
Conservation 78: 171-181.