Plant competition
—Methods and Theory
Lei Ba Associate Professor
Institute of Grassland Science
Key laboratory of Vegetation, the Ministry of Education

Survival of the fittest
Interaction in nature
► Basic
forms of interactions among organisms
 Positive（+），表示对种群存活、增长或其他特征有益。
 Negative（-），表示对种群存活、增长或其他特征有抑制。
 No effect（0），表示两个种群之间的关系无关紧要
Interaction in nature
Interaction
coexistenc
e
separation
相互作用的一般特征
A
B
A
B
Competition
-
-
0
0
两种种群在群落中的存在，对各自的增长甚至存
活都有抑制作用。
Mutualism
+
+
0
0
两个种群在群落中的存在，对各自增长和存活都
有相互促进作用。
Commensali
sm
Amensalism
+
0
-
0
两个种群在群落中的存在，A种群对B种群的增长
有促进作用；而B种群对A种群没有影响。
-
0
+
0
两个种群在群落中的存在，A种群对B种群的增长
有抑制作用；而B种群对A种群的增长没有影响。
parasitism
+
-
-
0
一个寄生种群对另一个寄主种群的增长有抑制作
用，而寄主种群必然对寄生种群有利。
Predation
+
-
-
0
一个捕食种群对另一个被捕食种群的增长有抑制
作用，而被捕食种群必然对捕食种群有利。
Neutrality
0
0
0
0
存在于群落中的两个种群，彼此对各自的增长与
存活没有什么影响，生态关系不密切。
What is competition——Concept
► Significance：Competition as a important selective agent
for all types of organisms (Darwin, 1958).
One of the major forces shaping the morphology and life
history of plant and the structure and dynamics of plant
communities.
The driving force behind evolution and natural selection.
► Application
in theory: Biodiversity; Community structure;
Complexity and stability of ecosystem
► Application in practice: Mixed turf with grass and legume;
Interaction between crops and weeds (weed control); Invasion of
exotic plants; Grassland degradation
What is competition——Concept
► Competition（Biology）
•
Negative relationship between two or more
organism or species through direct or indirect
interaction.
•
An interaction among individuals utilizing a
limited resource (food, space, shelter, mate,
ecological status, etc), resulting in a reduced fitness
(growth, reproduction and survival etc) in the
competing individuals. —— Begon, 1990
Classification of competition
► Biological
group: intraspecific and interspecific CP
► Interactive
way: exploitation and interference CP
► Effects:
symmetry and asymmetry CP
► Influences:
contest and scramble CP
► Way：direct
and indirect CP
scramble
contest
Competition
Direct
Indirect

Effects of one species
impact another species
indirectly

Apparent Competition
Exploitative Competition

Animals: physical combat
Plants: release of toxins
Classification of competition
Some possible type of traditional and apparent interspecific
competition
Connell, 1990
Intraspecfic competition





Competition
Fighting
Sex
Territory
Social rank
Individual size
Asymmetry competition
Intraspecfic competition
Density dependent of plant population
(the relationship between fitness and population size.)
Basic theory:
► Density dependent regulation can make different
size individuals population to be a population of a
consistent density
► High density of small seedlings into a low density
of matures
► Leads to ‘Law of constant final yield’
Intraspecfic competition
Law of constant final yield：
Yield is constant over a
wide range of densities
for many wild plants.
Total yield (kg m-2)
Density dependence of plant population
Plant population density
 Plants at high densities are unable to grow to a large
size. High density is offset by poor individual growth.
Intraspecfic competition
Density dependence of animal population
Limpets
植物种群的密度制约的基本理论
 所有密度制约的结果是将最初大小不一的种
群变成大体上具有恒定密度的种群
 密度制约的死亡可使大的幼苗密度降至幅度
较小的成年株密度
 密度制约的生育力可使密度相差悬殊的植物
种群产生近似数量的种子即所谓“最终产量
恒定法则最终产量恒定法则
Intraspecfic competition
►Self-thinning: In an even-aged group of sessile
organisms, competing individuals can not escape, and
植物种群的密度制约的基本理论
typically competition results in the survival of fewer
individuals
所有密度制约的结果是将最初大小不一的种群变成
of larger size.
大体上具有恒定密度的种群
►－3/2
密度制约的死亡可使大的幼苗密度降至幅度较小的
law (Yoda): Self-thinning results in a relationship
between
density and individual mass, which typically has
成年株密度
a
slope
of
－3/2
on
a
log-log
plot
as:
 密度制约的生育力可使密度相差悬殊的植物种群产
W = C d-a
生近似数量的种子即所谓“最终产量
or ㏒W = ㏒C - a㏒d
Log10 mean dry
weight per plant
Self-thinning
Path followed by a growing
population of plants
Shade?
Infertile soil?
Log10 number of survivors (ha-1)
植物种群的密度制约的基本理论
 所有密度制约的结果是将最初大小不一的种群变成
大体上具有恒定密度的种群
 密度制约的死亡可使大的幼苗密度降至幅度较小的
成年株密度
 密度制约的生育力可使密度相差悬殊的植物种群产
生近似数量的种子即所谓“最终产量
Interspecfic competition
Competitive exclusion principle (Gause's law):
Two species competing for the same resources
cannot coexist if other ecological factors are constant.
When one species has even the slightest advantage or
edge over another, then the one with the advantage
will dominate in the long term. One of the two
competitors will always overcome the other, leading to
either the extinction of this competitor or an
evolutionary or behavioral shift towards a different
ecological niche. The principle has been paraphrased
into the maxim "complete competitors cannot coexist".
Interspecfic competition
Relative population density
High
Low
0
Paramecium
aurelia
Paramecium
caudatum
2
4
6
8
10
12
14
Days
Each species grown alone
16
18 0
2
4
6
8
10
12
14
Days
Both species grown together
16
18
Interspecfic competition
Competitive exclusion principle (Gause's law):
If two species have the exact same requirements
(NICHE) in the same place - they cannot coexist.
Georgii Frantsevich Gause
Born 1910
Interspecfic competition
Concepts of niche：
Niche: a term describing the relational position of a species
or population in its ecosystem to each other; A shorthand
definition of niche is how an organism makes a living.
Fundamental niche: An organism free of interference from
other species could use the full range of conditions (biotic and
abiotic) and resources in which it could survive and reproduce.
Realized niche: as a result of pressure from, and interactions
with, other organisms (i.e. inter-specific competition) species are
usually forced to occupy a niche that is narrower than this, and
to which they are mostly highly adapted.
Interspecfic competition
A species distribution is
controlled by just two
environmental variables:
temperature and moisture.
The green and yellow areas
describe the combinations
of temperature and
moisture that the species
requires for survival and
reproduction in its habitat.
This resource space is known as the fundamental niche. The green
area describes the actual combinations of these two variables that
the species utilizes in its habitat. This subset of the fundamental
niche is known as the realized niche.
Niche theory
Species X
Species Y
Niche overlap
—Competition;
Niche separation
—Coexistence.
Species X
Species Y
Research Methods
Associate species
Focal species
Resource
Focal species
Additive design
Associate
N associate
Monoculture of focal
N focal species
Substitutive design (replacement series)
Monoculture of
associate
N associate
Monoculture of
focal
N focal species
Response surface
Monocultures of
associate
N associate
Monocultures of
focal
N focal species
1. What two factors/processes are confounded
in your experimental design?
2. Which type of competition question can your
design answer? Which can it not?
Some possible types of competition questions
•Does associate species X affect focal species Y?
Additive
•How does interspecific competition (effect of X on Y)
compare to intraspecific competition (effect of Y on Y)?
Substitutive
•Is competition asymetrical? That is, does either X
affect Y more than Y affect X, or vice versa?
•Is the strength of competition dependent on the
density of the associate species (X)? Density of the
focal species (Y)? Additive
L-shaped additive or substitutive
Research Methods for 地上和地下竞争
Pot separation method:
Research Methods for 地上和地下竞争
Line separation method:
Research Methods for 地上和地下竞争
Target species method
Index for evaluating competition
Using Biomass
Using RGR
NN: No competition, NRS: full competition; NR: root competition
Factors influence competition
Differences among species in competitive ability：
在群落中,物种竞争能力的大小可以排成竞争等级，
其等级不受目标种和邻居种选择的影响。
►竞争能力的差异可能由扎根类型和深度、植株大小、生长
率、高度、截留光的能力或其他特征决定。由于竞争能力是
植物的综合能力，它应该由植物的形态，生理及生活史特征
共同决定。此外，环境条件和资源水平对物种竞争能力有深
刻的影响。如果不同物种对这些变化有不同的反应，那么竞
争等级会随之改变，但我们并不知道如何变化。
►研究植物群落中竞争等级相对于环境条件和资源有效性的
类型是十分有意义(Keddy et al., 1994)。
Factors influence competition
Nutrient availability: 有些种能更有效地利用所添加
的营养。例如，杂草和作物对营养有效性的反应不
同；在其它的自然植被中也存在物种间差异。
►常见的问题是:在资源水平变化的条件下，什么性状决定
其竞争能力以及这些性状是如何受到资源水平和环境生产力
调节的呢？响竞争力的特征可归纳为四类：(1) 影响植物捕
获资源能力的特征； (2) 植株的初始大小或质量；(3)影响转
化捕获资源成生物量效率的能力； (4) 植株生长的可塑性。
然而, 对其机制的认识还需更多的理论(如模拟) 和实验工作
才能实现（Grace & Tilman, 1990） 。
Factors influence competition
Emerging time：幼苗出土时间是决定植物竞争能
力的重要因素。一些研究表明：早出土的幼苗不仅
有较长的生长时间,而且还具有竞争优势。
2.7
7
Type of communty
羊草群落
2.3
3
混生群落
2.5
1
芦苇群落
3.9
5
2.0
2.5
3.0
3.5
4.0
距地面深度 Deepth to soil surface
4.5
(cm)
L. chinensis
P. communis
Factors influence competition
Spatial pattern：植物不能运动,所以种群个体的空
间分布是决定竞争结果和种群动态的重要因素。所
有植物竞争相同的资源和空间,所以植物间越靠近,
对资源和空间的竞争就越强烈。
►在作物-杂草系统中,实际上斑块状分布的杂草对作物的竞
争影响比假设的随机分布的杂草竞争能力弱。
►在自然分布的植物群落中,分布格局是如何影响共存物种
的竞争能力仍是一个没有得到认识的问题。
Factors influence competition
空间分布：
物种交错带处，植物空间格局对竞争的影响
Factors influence competition
样带 时间
格局分布类型
样带 时间
格局分布类型
Ⅰ 5月 ○ ▲ ○ ▲ △ ▲ ○ ● ○ ▲ △ ●
Ⅳ 5月 △
△
○ ● ○ ● ○ ●
▲
●
6月 △ ▲ △ ▲ △ ● △ ▲ △ ▲ ○ ●
6月 ○
△
△ ● △ ● ○ ● △ ●
●
7月 ○ ▲ △ ▲ △ ● △ ● ○ ▲ ○ ▲
7月 △
△
○ ● ○ ● ○ ●
●
●
8月 ○ ▲ △ ▲ △ ● △ ▲ ○ ▲ ○ ▲
8月 △
△
○ ● △ ● ○ ▲
●
●
Ⅱ 5月 ○
△
△ ● △ ▲ △ ▲ △ ▲
Ⅴ 5月 △
△
△
○ ● ○ ▲ △ ▲
6月 △
△
○ ▲ △ ▲ △ ▲ △ ▲
6月 △
○
△
○ ● △ ▲ △ ▲
7月 △
△
○ ▲ △ ▲ △ ● △ ▲
7月 ○
△
△
○ ● △ ● △ ▲
8月 △
○
○ ▲ ○ ▲ △ ▲ △ ▲
8月 ○
△
△
○ ▲
Ⅲ 5月 △
△
△
△ ● △ ▲ ○ ● △ ●
Ⅵ 5月 △
○
△
△ ▲ △ ● △ ▲ ○ ▲
6月 △
△
△
△ ▲ △ ● △ ▲ △ ■
6月 △
△
△
○ ▲ △ ▲ △ ● △ ■
7月 △
○
△
○ ● △ ●
▲
▲
7月 ○
○
△
△ ▲ △ ● ○ ▲ ○ ▲
8月 △
○
△
○ ● ○ ●
▲
●
8月 △
○
○
○ ● ○ ▲ △ ▲
○代表羊草集聚分布, △代表羊草随机分布, ●代表主要伴生种集聚分布, ▲代
表主要伴生种随机分布, ■代表主要伴生种均匀分布
▲
▲ △ ▲
Factors influence competition
群落类型
羊草、芦苇
混生群落
羊草、芦苇
交错带
群落
序号
羊草 L. chinensis
芦苇 P. communis
平均
拥挤
聚块
指数
集聚
参数
平均
拥挤
聚块
指数
集聚
参数
Ⅰ
Ⅱ
Ⅲ
22.880
1.052
19.245
8.054
1.284
3.183
18.088
1.168
5.969
16.355
1.202
1.202
26.862
1.104
9.592
5.767
2.241
0.869
Ⅳ
Ⅴ
Ⅵ
29.769
1.549
0.343
8.046
1.650
1.814
47.360
1.679
0.306
11.039
1.655
1.310
28.041
1.310
0.649
5.803
2.251
0.421
混生群落和交错带中羊草和芦苇的格局强度
混生群落和交错带中羊草和芦苇的格局强度
Factors influence competition
AMF：真菌不仅能够直接引起植物生理上的反应
外,它还可能导致植物与其他营养级生物之间相互
作用的变化,从而间接地影响植物的竞争能力。
Herbivory：选择性采食、践踏、微生物等都影
响植物生长和对营养的获取能力
Theories of competition
Grime-CSR model（1979）： Two main environmental
variables that dictate plant life history traits: Disturbance and Stress
►High Disturbance, Low Stress: Ruderal plants
Grow quickly, reproduce rapidly, produce large numbers of
seeds
►Low Disturbance, High Stress: Stress Tolerant plants
Grow slowly, conserve resources for periodic reproduction
when conditions are favorable; low competition
►Low Disturbance, Low Stress: Competitive plants
Can grow quickly, but eventually will compete for resources;
life history will maximize competitive advantage (e.g.,
later maturity; large size; fewer, larger offspring)
Theories of competition
Grime-CSR model（1979）：
Ruderals
Increasing
disturbance
Increasing
Disturbance
(more disturbed
habitats)
(DisturbanceTolerant
Organisms)
Competitive
organisms
Increasing
stress
Stress-tolerant
organisms
Increasing stress
(more severe habitats)
Theories of competition
Theories of competition
Tilman：R* model
当资源被利用，资源量下降到一个水平
R*（ R*是资源量平衡点）时，如果低
于平衡点R*，种群就不能够维持自身生
长，所以具有最低R*的种群，将会在竞
争中取胜，而竞争的发生取决于资源量
R*。如果一个种所获得的资源量大于R*，
这个种群就会增长。反之，就会减少。
对资源量R*具有较低要的种群具有更好
的竞争能力
Mechanisms of Competition
1. Consumptive – one species competes with
another by consuming a shared resource
Brown and Davidson 1977
2. Preemptive – occupation of physical habitat by
one species, thereby excluding another
invasive Salvinia
Swamp Forest Understory
3. Overgrowth – one species grows over another
4. Chemical – “chemical warfare”

allelopathy in plants; has not been convincingly
demonstrated
Bare zones in California chaparral
Allelopathy among shrubs (Muller 1969)
5. Territorial – aggressive behavioral exclusion
Gray reef shark
6. Encounter – nonterritorial encounters between foraging
species

wasted time/energy that could’ve been devoted to
reproductive output
Example:
parasitoid
wasp species