Download Plant Ecology

Plant Community EcologyPlant Interactions
(competition/facilitation)
Competition
Reduction in fitness (how an
organism apportions resources
among competing demographic
functions (survival, growth,
due to shared
use of a resource that is in
limited supply
Intraspecific
reproduction)
Interspecific
Plants can tell the difference between the shade of an inanimate object and the shade
of another plant. When a plant detects competition from neighboring plants, it initiates
a set of responses, called collectively the shade avoidance syndrome, that alter its
growth and physiology. A rapid and transient increase of newly synthesized auxin via a
newly discovered auxin synthesis pathway allows plants to elongate and grow toward
the sun.
Competition
- / - both parties lose
0 / - or + / - asymmetric competition - largest
individuals have disproportionate negative effects
on their smaller neighbors
Competition
Tall plants may intercept light, but small plants
may intercept water, soil nutrients
Asymmetric, but larger plants usually have much
greater effects
Competition
Trade-offs and strategies
Winning competition for one resource may compromise ability to win
comp. for another (light vs. nutrients)
Outcome may change as resource availability changes
Competition
Immediate density most important - average
density essentially irrelevant
Effects of neighbors decrease sharply with
distance
DEBATE between Grime and Tilman (1980s) regarding
the effects of competition on species coexistence
and community composition
Resource competition-tendency of neighboring plants to
utilize the same quantum of light, ion of a mineral
nutrient, molecule of water, or volume of space
Both believe that understanding plant traits, resource
acquisition and loss by plants and the effect of
disturbance on individuals holds the key to understanding
patterns of diversity
GRIME CRS Theory regarding the effects of
competition on species coexistence and community
composition
 In high productive environments, competitors that
confer rapid growth rates will always dominate
 Competition is unimportant in unproductive
environments and success is dependent onthe ability to
tolerate abiotic stress
 In unproductive habitats species have characteristics
that confer stress tolerance, such as long-lived leaves
with high nutrient retention rates (biggest contrast with
Tilman’s R theory)
In disturbed habitats plant have traits that allow them
to withstand disturbance or high dispersal ability that
allows them to recolonize rapidly
Grime’s Triangular Model
TILMAN R* (Resource-Ratio ) Theory regarding the
effects of competition on species coexistence and
community composition
 Extended MacArthur (1972)—niche theory ideas on plant
competitive strategies
R* is the concentration of available resource that a species requires
to survive in a habitat … If all species are limited by the same nutrient,
the species with the lowest R* should displace all competitors.
Tilman (1987) stated that competition in low productive sites would
be for belowground resources and in productive sites for aboveground
resources (light).
In unproductive habitats, superior competitive ability depends on the
ability to reduce soil nutrients to a level below that at which
competitors can exist and to persist at that this low level
Change in resource levels over time occurs because of incorporation of resources into
the biomass of the plant population. (1) The population starts at a high resource level.
Growth by the population results in the uptake of resources which are incorporated into
standing biomass. This in turn results in the (2) decrease of available resources in the
environment. This process continues until there is a (3) dynamic balance between
resource uptake due to growth and resource release due to mortality. Essentially b=d
and the population size remains fairly constant and resource levels are held at the level
of R*, the minimum resource level for the maintenance of the population.
If two species are competing for the same resource, the species that can
grow at the lowest resource levels will be able to drive the other species out of
the system. Species B above will outcompete species A, since it can exist at
lower resource levels
Craine 2005 Journal of Ecology-critiqued Grime and
Tilman’s theories
General Overview of effects of competition on
species coexistence and community composition
 Ecologists agree that competition is intense in
productive, nutrient-rich habitats when herbivory and
disturbance is low
 Importance in unproductive habitats remains
debatable because environments can be unproductive
for a variety of reasons (low water supply, cold temps,
short growing season, saline soil, toxic metals)
Future Research: reducing vast diversity of terrestrial
plants to conceptual categories so that plants can be
grouped in ways that enable one to pose testable
hypotheses and make predictions
Allelopathy
Chemical warfare among neighboring plants
Release toxins into soil to reduce growth or kill adjacent plants
Way to gain competitive advantage
Knapweed on rangelands - little effect on Eurasian plants, strong
effects on N. Amer. plants
Plants influence their environments in many ways—
altering balance of nutrients, acidifying the rhizosphere,
secreting materials, and shedding parts. Plant can also
affect soil microbes that affect other plants (indirect)
Allelopathy?
Artemisia californica
FUTURE RESEARCH-ALLELOPATHY
Need to know the concentrations and release rates of
hypothesized allelochemicals, followed by experiments to
manipulate concentrations of chemicals
Need to link greenhouse studies with large-scale field
manipulations to bring clarity to subject
 Need to know how plants change their soil environment
and how these changes affect their interactions with both
conspecifics and competitors?
Facilitation
Positive effects on neighbors rather than negative
(opposite of competition?)
May be particularly common under conditions of high
abiotic stress, or high herbivory
Facilitation
Neighbors’ effects differ
depending on other aspects
of the environment
Falcataria spp.
Eucalyptus spp.
Eucalyptus benefitted at high P to be
near Falcataria but had negative
competition interactions with
Eucalyptus at low P
Facilitation-nurse plants
Mature “nurse” plant
may facilitate
germination,
establishment, growth
of juvenile plant of a
different growth form;
increase soil moisture,
decrease temperature
and light intensity
Facilitation-CMNs
Common mycorrhizal
networks - extensive
connections linking
many plants of differing
age, species
May facilitate seedling
and sapling survival and
growth by way of
nutrient and water
transfers among plants
Mature helping juvenile
Mycorrhizae
Symbioses between mycelium of a fungus with roots
of terrestrial plants
Mutualism or Parasitism?
Fungi get carbon, energy from plant host
Plant gets nutrients, other benefits
Either “partner” can function as parasite at times - plant
sheds fungus when times are good, or fungus gives little
to plant
Mycorrhizae
Arbuscular mycorrhizae
- most abundant where
phosphorus is limited, in
warm, dry climates
Important in tropical
ecosystems, and for
crop pants - woody and
herbaceous
Fungal body grows
inside root cells, with
hyphae extending
outward
Mycorrhizae
Ectomycorrhizae woody plants,
especially temperate
conifers
Hartig net between
root cells, mantle
network of hyphae
outside root
Mycorrhizae
Fungal hyphae increase nutrient uptake from soil
Transfer nutrients to root cells of host plants
Improve metal uptake
Improve water uptake
Break down soil proteins
Protect roots from toxins
Protect plant from fungal, bacterial diseases
http://www.youtube.com/watch?v=bq1bTduTzC0