Download Plant competition

Kompetice
rostlin
and maintenance of
species diversity in
plant communities
Definice kompetice
Důsledky přisedlého způsobu života
Typy kompetice
Komponenty kompetice o zdroje (resource
competition)
Modely
Grime vs. Tilman
Empirické studie - pozorování a manipulativní
experimenty
Species coexistence as violation of competitive
exclusion principle
Gradients of species diversity and their causes
Jak definovat kompetici?
Grace (1990): “The variety of possible definitions of
competition were discussed and it is safe to say that
there is no universally accepted definition.”
Možnosti:
Podle efektu: interakce - - (obě populace jsou
ovlivněny negativně. Velmi široká definice)
Podle mechanismu: Grime: “The tendency of
neighbouring plants to utilise the same resources”
(velmi úzká definice)
Řada dalších definic (někde mezi)
Rostlinná kompetice:
Rostliny jsou sedentární, takže:
Konkurence probíhá jen mezi sousedy důležitost prostorové struktury a heterogenity
Jsou ovlivněny heterogenitou prostředí (velká
morfologická plasticita jako řešení)
Zůstávjí během celého života na jednom místě
Velikost individua je důležitější druhová identita
(dospělý smrk lehce potlačí dospělou
Calamagrostis ale dospělá Calamagrostis
zahubí smrkový semenáč)
Kompetice je velmi asymetrická (zvláště
kompetice o světlo)
Typy kompetice
Obr. Connell
Negativní efekt zprostředkovaný ohněm (strategie: Ať
mě chcípne koza, hlavně když sousedovi chcípne
kráva!)
Allelopathy: release of toxic chemicals to the soil (to
prevent germination and growth)
Problems - how to demonstrate experimentally?
Similar effect - production of litter with low decay
rate
Apparent competition
Low birches (Betula
nana) are under higher
herbivor pressure under
congeneric Betula
tortuosa.
Resource competition
Resource must be limiting, in restricted amount, and in
common use
Components of
resource
competition
Both relationships
must operate
simultaneously. If
not, there is no
effect of one
species on another
Plant affects both resource and non-resource
characteristics (Tree decreases light by shading, but
could protect from overheating)
Effect is not always detrimental
Facilitation (usually in stressed environments, or
in stress periods)
[Gap effect on transplant growth was highly
positive during a wet year, but highly negative
during dry year]
Classical Lotka-Volterra competition model
dN1
K1  N1  N 2
r 1N1
dt
K1
dN 2
K 2  N 2  N1
r 2 N 2
dt
K2
Stable equilibrium if
  K1 / K2
and
  K2 / K1
i.e., when the inhibitive effect of each species on its own
population is bigger than on the competitor (scaled by the
corresponding K) => niche differentiation
Tilman’s theory: the species with lower R* is the winner
(i.e. species, able to growth in the lowest concentration of
the resources)
Population
Resource
According to the theory, number of coexisting species can not
exceed the number of limiting resources
Plant compete for light and [water and nutrients] (and often
tens of species coexist on a small area)
Competition for pollinators, seed dispersers
Competition for space - the aboveground space is far
from being filled by plant mass.
“Competition for space” - the way sedentary
organisms attempt to monopolise the resources.
Grime vs. Tilman
What is measure of competition success
What are the trait of successful competitors (Grime ability to capture the resources, high RGR, Tilman
ability to grow at low resource levels, i.e. low R*)
Importance of time scale
Empirical studies of competition
1. (Indirect) From (spatial) pattern
2. (Direct) Manipulative experiments
a) planting (sowing) monocultures and mixtures
b) transplanting (e.g. into a sward and into a gap)
c) removal of vegetation in surrounding of target
d) removal a species from a community
Regular (uniform) spatial patter is most probably
consequence of increased mortality due to neighbours
competition
Aggregated (clumped) pattern has many causes, positive
interactions being just one of less probable. (Most
common: environmental heterogeneity, dispersal.)
Changes in the pattern in the course of time are better
evidence than static pattern.
Correlating the available space (or quantity of neighbours)
with performance of the individual. [Danger of the
confounding factors, reverse causality, etc.] Eccentricity of the
root system
Experimental approaches
Growing plants in monocultures
and together
Long tradition in agricultural research
Pot competition experiment
with Holcus lanatus,
Lychnis flos cuculi
and their mixture at different
nutrient levels
Additive design vs. replacement series
Transplant experiments Prunella vulgaris
J
Hg
M
0
8.0
11.0
6.0
8.3
4.0
5.5
2.0
2.8
0.0
270
Sg
Ng
0
0.0
90
270
90
N
180
180
3
.
2
M
ay9
a
ab
ab
c
M
ay31
bc
Jul 3
bc
2
.
6
Meaninternodelength(cm)
2
.
0
1
.
4
0
.
8
0
.
2
N
a
r
d
u
s
J
u
n
c
u
s
M
o
l
i
n
i
a
T
re
a
tm
e
n
t
S
q
u
a
r
e
N
a
t
u
r
a
l
H
a
l
f
Clonal plant’s reaction
to competition - increase
of stolon length and
orientation of stolons to
“competition free” part
Lychnis flos cuculi
Tradeoff between flowering (in competitive
environment) and producing secondary rosettes (in
gaps)
100
J
90
N
%of floweringplants
80
S
G
70
B
G
M
60
50
0.0
0.4
0.8
1.2
1.6
N
um
berof thesecondaryrosettes
2.0
2.4
Removal of vegetation around target individuals
Attempts to separate above- and
belowground competition
Dominant removal from a community
2
BIOMASS [g/0.25m ]
TOTAL and Molinia
180
160
140
120
100
80
60
40
20
0
CONTROL: TOTAL
REMOVAL: TOTAL
CONTROL: Molinia
1995 1996 1997
UNFERTILIZED
1995 1996 1997
FERTILIZED
Species coexistence: can be seen as a violation of the
competitive exclusion principle
Competitive exclusion principle: two species can not coexist for
indefinitely long time in a homogeneous environment
The equilibrium and non-equilibrium explanations
Equilibrium: Environment is not homogeneous (niche
differentiation)
Non-equilibrium: time is not sufficient
Medium disturbance hypothesis
Repeated disturbance of
medium intensity or
frequency is able to
prolong species
coexistence
What is medium depends on the productivity
Density dependence - parasites & predators
Janzen hypothesis
- species diversity
in tropics
Gradients of species diversity
Tree species richness
in Canada and the
United States.
Contours connect
points with the same
approximate number
of species per quadrat.
Quadrat size is 2.5˚ x
2.5˚ south of 50˚N,
and 2.5˚ x 5˚ north of
50˚N (Currie and
Paquin 1987).
Diversity usually
decreases at very low
and very high
productivity
Explanations of
gradients of species
diversity:
1. by community
mechanisms
2. by species pool
Diversity decrease at high nutrient levels:
some of the hypotheses
- less species adapted to high nutrient levels
- higher competition at high nutrients (Grime)
- switch from underground competition to competition
for light (which is more asymmetric)
- suppressed seedling recruitment
Seedling recruitment of Gentiana pneumonanthe
mown
burned gap
control