1. Lecture 5: Competition Huang He Phone: 18972127775 QQ:105367750
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2019/2/16

2. Modes of Competition
Competition: use or defense of a resource by one individual that reduces the availability of the resource to other individuals
Intraspecific:
Competition with members of own species.
Interspecific:
Competition between individuals of different species - reduces fitness of both.

3. An experiment demonstrating competition of two species
A.G. Tansley (1917)
British botanist
Two small perennial herbaceous plant species
Two kinds of soils
G. Saxatile grow on acidic peaty soils
G. Sylestre on alkaline soils of limestone hills
Pioneering work
perennial 英 [pə‘renɪəl] 美 [pə’rɛnɪəl] adj. 多年生的；常年的；四季不断的；常在的；反复的n. 多年生植物
herbaceous 英 [hɜː'beɪʃəs] 美 [ɝ'beʃəs] adj. 草本的；绿色的；叶状的
peaty 美 ['piti] adj. 多泥煤的；泥煤似的
calcareousadj. 钙质的，石灰质的 n. 钙化软骨
Species are generally restricted to the most favorable soil type when competiting species are present, but may be broadly distributed over other soil type in the absence of competition.

4. Competition results when resources are limited
2/16/2019
Competition results when resources are limited
Intraspecific competition: regulate population growth in a density-dependent manner.
Evolution tends to favor the individuals with high resource use efficiency and competition ability
Interspecific competition: depress both populations. Under intense interspecific competition, population of one species may decline and die out.
Outcome of interspecific competition:
depends on how efficiently individuals within each species exploit share resources.
Socialism, Capitalism
As long as availablility of resources does not impede the ability of individuals to survive, grow, and reproduce, no competition exists.
When recouses are insufficient, competition occurs.
If resource is not limited, all individuals can get enough food for them to grow, reproduce, there is no competition.
Another point of view of competition: explo, and inter.

5. Supercompetitor can persist at lower resource levels
As population grow, resource available for each individual decreases
Resources and competition

6. Outline 5.1 Consumers compete for resources
5.2 Failure of species to coexist in laboratory cultures led to competitive exclusion principle
5.3 The theory of competition and coexistence is an extension of logistic growth models
5.4 Asymmetric competition can occur when different factors limit the populations of competitors
5.5 Habitat productivity can influence competition between plant species
5.6 Competition may occur through direct interference
5.7 Consumers can influence the outcome of competition

7. 5.1 Consumers compete for resources
Resource: any substance or factor that is both consumed by an organism and supports increased population growth rates as its availability in the environment increases
Examples:
food, water, nutrient,
light, space
Refuges, safe site
No-consumeable physical and biological factors are not resource: Temperature is not consumed, one does not change T for another
Three things: 1. comsumed, 2. used for growth; 3. negatively influence if not available

8. Space is an important resource for sessile animals
sessile 英 [‘sesaɪl; ’sesɪl] 美 [‘sɛsl] adj. 无柄的；固着的[植](花,叶等)无柄的, 固着的
barnacles 英 [‘bɑːnəklz]n. 藤壶（barnacle的复数）；刑具甲壳动物
intertidal zone [海]潮间带
larva幼虫
Barnacles on the rocky coast of Maine. Above optimal range of intertidal zone (small ones are larvae)

9. 5.1.2 Competition between closely and distantly related species
Which one is more intense, closely related species or distantly远的, 关系远的(亲戚) related species?
On the Origin of Species:
Competition should be most intense between closely related species
Structure, Habitat, food resources
Similar to intraspecific competition, some different species also share the same common resources
Competition in different forms

10. Competition between distantly related species
Example 1: barnacles藤壶 , mussels[动]贻贝, 蚌类, alage, sponges, bryozoans苔藓虫, tunicates【动】被囊类动物in the intertidal zone compete for spaces
Example 2: fish, squid鱿鱼, diving birds, seals, and whales all eat krills[单复同] n.[动]磷虾
Example 3: spiders, ground beetles, salamanders, and birds consume invertebrates无脊椎动物living in the forest litter
Example 4: birds, lizards eat same insects; Ants, rodents, birds eat seeds in the desert systems.
Distantly species may use the same resources bryozoans苔藓虫。 tunicate【动】被囊类动物。 squid鱿鱼。 beetles甲虫。 salamander[动]火蜥蜴, 火怪, 耐火的人。 lizard[动]蜥蜴。 rodent啮齿动物
mussels[ˈmʌslz] n. 贻贝，蚌类( mussel的名词复数 )
sponge[英] [spʌndʒ] [美] [spʌndʒ] n. 海绵； 海绵状物 vt. （用海绵）擦拭 vt.& vi. 骗取； 敲詐
bryozoan[英] [ˌbraiəˈzəuən] [美] [ˌbraɪəˈzoən] n. 苔藓虫 adj. 苔藓虫类的

11. 5.1.3 Renewable and nonrenewable resources
Renewable: constantly renewed or regenerated
Natural resources outside ecosystem: such as light and precipitation
Resource regenerated
Birth of prey provide foods for predator
Consumers directly depress such resources
Decomposition provide nutrients for plants
Indirectly linked to consumers through food chain or abiotic factors非生物因子[因素].
Non-renewable: space
Once occupied, space becomes unavailable to others

12. Limiting resources
Consumers require many different resources, but not all resources limit population growth
Liebig’s law of minimum
Populations are limited by the single resource that is most scarce relative to demand
Justus von Liebig (1840)
Limiting resources: may vary
David Tilman’s diatom study: both P and silicon
<0.2 mM of phosphate
or <0.6 mM silicate, diatom pop.growth stops.
Slowest process
Lowest block in a basket diatom硅藻
Liebig’s law of minimum 李比希最小因子法则

13. 5.1.5 Positive interaction and synergistic effect
Synergistic effect协同效应: Two resources together enhances population growth more than the sum of both individually
Peace and Grubb (1982)
Plant fertilization and
Light treatments
Effects: N ~0.4, P ~0.2, N+P: 0.9
Antagonistic: decrease more than the sum of two alone
Positive interaction正相互作用
synergistic增效的， 协作的， 互相作用[促进]的 synergistic[英] [ˌsɪnəˈdʒɪstɪk] [美] [ˌsɪnɚˈdʒɪstɪk]
协同作用 英文名称： synergism 定义1： 一种污染物因另一种污染物的存在而使其毒性增强的作用。 应用学科：生态学（一级学科）；污染生态学（二级学科） 定义2： 两种或多种物质协同地起作用，其效果比每种物质单独起作用的效果之和大得多的现象。 应用学科： 生物化学与分子生物学（一级学科）；总论（二级学科）

14. 5.2 Failure of species to coexist in laboratory cultures led to the competitive exclusion principle
G.F. Gause, Russian biologist
Protist: (bacteria here)
P. aurelia and P. caudatum
Same nutrient medium
exclusion principle排他原理, 不相容原理
Russian biologist G.F. Gause
Competition between two species
P. aurelia has a high growth rate and can tolerate a higher population density
Two Paramecium (unicellular ciliated protozoan)
One with higher rate of growth: Extinction of slower grower

15. Diatom experiment David Tilman, University of Minnesota
Asterinella formosa (Af) and Synedra ulna(Su) compete for silica for the formation of cell walls.
Grow well alone
Insufficient silica, Su reduced the silica to a low level and drove Af to extinction
any microscopic unicellular alga单细胞藻类of the phylum Bacillariophyta, occurring in marine or fresh water singly or in colonies, each cell having a cell wall made of two halves and impregnated with silica.
Asterinella formosa美丽星杆藻 Synedra ulnan.  肘状针杆藻

16. Competitive exclusion principle
Principle: Complete competitors can not coexist. One species must go extinction
Complete competitors: two species that live in the same place and possess exactly the same ecological requirements.
Assumptions:
Exactly the same resource requirement (no more, no less)
Environmental conditions remain constant
In natural situations, two similar species can coexist, why?
Model predict that 3 out of 4 conditions one species will go extinction. (Stable equilibrium is rare and has strict requirement).
In lab, the above example showed that species can not co-exist, if they are complete competitors.
Competitive exclusion principle竞争排斥原理

17. 5.3 The theory of competition and coexistence is an extension of logistic growth model (Lokta-Volterra Model)
Derived from logistic growth equation
Add influence of another species (a competition component)
Alpha and beta are per capita competition coefficients that quantify the per capita effects of one species on another species
In resource use, 1 individual of species 1 is equal to beta individuals of species 2.
Rabbit and sheep: one sheep is equal to 50 rabbits

18. Lokta-Volterra Model
α2,1N2 and α1,2N1: effect of interspecific种间的competition, where α2,1 and α1,2 per capita effects of competition
In term of resource use, an individual of species 2 is equal to α2,1 individuals of species 1
2019/2/16

19. 5.3.2 Interspecific competition reduces the equilibrium level of a population below the carrying capacity
Intraspecific [生]种内的 interspecific 种间的

20. 5.3.3 If no interspecific competition
Species 1: dN1/dt = r1N1 ((K1 – N1 – 1,2N2)/K1)
In the absence of interspecific competition, 1,2 = 0 and N2 = 0  the population of species 1 grows logistically to carrying capacity
Species 2: dN2/dt = r2N2 ((K2 – N2 – 2,1 N1)/K2)
In the absence of interspecific competition, 2,1 = 0 and N1 = 0  the population of species 2 grows logistically to carrying capacity

21. (a) Species 1 N2=(K1-N1)/alpha Alpha=alpha1,2
isocline   英 ['aɪsə(ʊ)klaɪn]  美 ['aɪsə,klaɪn]  n. [地物] 等斜线；等斜褶皱
diagonal  英 [daɪ‘æg(ə)n(ə)l]  美 [daɪ’æɡənl]  adj. 斜的；对角线的；斜纹的 n. 对角线；斜线
dN/dt=0, populations reach carrying capacity. Use one spp as example, N=K. N<K, increase; N>K, decrease
With the exist of species 2 and competition, the carrying capacity of species 1 changes: zero growth isocline
Need to explain dN1/dt=0, then N2=(K1-N1)/alpha, species reach its carrying capacity
How population 1 changes
No matter what the size of populatoin 2 is, species 1 can reach a stable population (carrying capacity)
somewhere (N1:K1—0; N2:0—K1/alpha).
Two populations
Diagonal斜的, 斜纹的, 对角线的line is zero growth isocline

22. (b) Species 2 N2=K2-beta N1 Beta=alpha2,1
With the exist of species 1 and competition, the carrying capacity of species 2 changes: zero growth isocline
Need to explain dN2/dt=0, then N2=K2-beta N1, species reach its carrying capacity
How population 2 changes

23. 5.3.4 There Are Four Possible Outcomes of Interspecific Competition
Possible outcomes of the Lotka–Volterra equations
In two situations, one of the species is the superior competitor and wins out over the other
In one case, species 1 inhibits the population of species 2 while continuing to increase
In one case, species 2 inhibits the population of species 1 while continuing to increase

24. (c) Species 1 inhibits growth of species 2 and latter goes extinction
Isocline of speices one falls outside species 2, species one wins

25. (d) Species 2 inhibits growth of species 1 and latter goes extinction
Isocline of speices 2 falls outside species 1, species 2 wins

26. 5.3.5 There Are Four Possible Outcomes of Interspecific Competition
Possible outcomes of the Lotka–Volterra equations
In a third situation, each species, when abundant, inhibits the growth of the other (more than it inhibits its own growth)
Eventually one of the two species “wins”
In a fourth situation, neither species eliminates the other resulting in coexistence
Each species inhibits its own population growth more than that of the other species
eliminates /ɪˈlɪmɪˌneɪt/ v 消除，排除

27. (e) Unstable situation, both inhibit in a density dependent manner
(e) Unstable situation, both inhibit in a density dependent manner. Depending on initial density, either can make other extinct

28. 2/16/2019
(f) Each species inhibits its own population growth more than competitor. Neither can eliminate competitor
eliminate排除, 消除

29. 2/16/2019
How to remember which wins?
Easy: large K wins, (c) K1 larger, species 1 wins, (d), K2 large, species 2 win, (e) one side sp1 wins, one side sp2 wins, (f) nobody wins, co-exist

30. （一）种间竞争 1、高斯假说 二、种间关系 有竞争、捕食、寄生和互利共生 2、 Lotka-Volterra种间竞争模型
竞争方程建立在逻辑斯谛方程的基础上.
dN1/dt=r1N1(k1-N1- α12N2)/k1
dN2/dt=r2N2(k2-N2- α21N1)/k2
k1、k2:两竞争物种的环境负荷
α12: 物种2的竞争系数,2对1的竞争抑制作用;
α21: 物种1的竞争系数,1对2的竞争抑制作用.

31. 2、 Lotka-Volterra种间竞争模型
dN1/dt=r1N1(k1-N1- α12N2)/k1
dN2/dt=r2N2(k2-N2- α21N1)/k2
dN1/dt= N1＝K1 - α12 N2
N1 = 0 , N2 = K1 /α12
N1 = K1 , N2 = 0
dN2/dt= N2＝K2 – α21 N1
N2 = 0 , N1 = K2 /α21
N2 = K2 , N1 = 0

32. 2、 Lotka-Volterra种间竞争模型
dN1/dt= N1＝K1 - α12 N2
N1 = 0 , N2 = K1 /α12
N1 = K1 , N2 = 0 N1 N2
K1/α12
dN1/dt<0
dN1/dt>0
dN1/dt=0 K1

33. 2、 Lotka-Volterra种间竞争模型
dN2/dt= N2＝K2 – α21 N1
N2 = 0 , N1 = K2 /α21
N2 = K2 , N1 = 0 N2
dN2/dt<0 K2
dN2/dt=0
dN2/dt>0 N1
K2/α21

34. · N1取胜, N2灭亡 K1 > K2 /α21,K2< K1/α12 N2 N1取胜,N2被排挤掉 K1/α12 K2

35. · N1灭亡, N2取胜 K1 < K2 /α21,K2> K1/α12 N2取胜,N1被排挤掉 N2 K2 K1/α12 K1

36. · 不稳定共存 N2 K2 K1/α12 K2/α21 K1 N1 K1 > K2 /α21,K2> K1/α12
N2和N1出现不稳定的平衡点 K2
K1/α12
K2/α21 K1 N1

37. · 稳定的共存 N2 K1/α12 K2 K1 K2/α21 N1 K1 < K2 /α21,K2< K1/α12
N2和N1被出现稳定的平衡点
K1/α12 K2 K1
K2/α21 N1

38. Coexistence on multiple resources
One reason is that the competitive ability is influence by many factors
Cyclotella小环藻属 Asterionella 星杆藻属
David Tilman: two diatom species, Cyclotella and Asterionella
Two Resouces: phosphorus (for DNA, phospholipids etc) and silicon (for shell)
Ratio of Si/P: if Si/P is below this level, silicon limited, above, phosphorus is limited
Cyclotella: Si/P=6, low requirement for Si, high for P
Asterionella: Si/P=90, high requirement for P, low for Si

39. 5.3.6 Asymmetric不均匀的, 不对称的competition can occur when different factors limit the populations of competitors
asymmetric[英] [ˌæsɪˈmetrɪk] [美] [ˌæsɪˈmɛtrɪk]不均匀的, 不对称的
desiccation 美 [,dɛsɪ'keʃən] n. 干燥
barnacle   英 ['bɑːnək(ə)l]  美 ['bɑrnəkl]  n. [无脊椎] 藤壶；茗荷介；难以摆脱的人；黑雁
In many cases of competition, the relationship between competitors is asymmetrical in the sense that each has an advantage with respect to different factors in the environ­ment. For example, one species might exploit resources more efficiently, while the other is better at tolerating stressful conditions or avoiding consumers. In many such cases of asymmetric competition, the competitors coexist locally in different microhabitats.
Connell demonstrated that adult Chthamalus are restricted to upper regions of the intertidal zone above Balanus not because of physiological tolerance limits, but because of interspecific competition. When Connell removed Balanus from rock surfaces, Chthamalus thrived in the lower regions of the intertidal zone where they normally do not occur. The two barnacle species compete directly for space. Balanus have heavier shells and grow more rapidly than Chthamalus; as individuals expand, the shells of Balanus edge underneath those of Chthamalus and literally pry them off the rock! Chthamalus can live in the upper intertidal zone because they are more resistant to desiccation than Balanus; even when surfaces in the upper intertidal zone are kept free of Chthamalus, Balanus do not invade.

40. niche 英 [niːʃ; nɪtʃ] 美 [niʃ] n
niche  英 [niːʃ; nɪtʃ]  美 [niʃ] n. 壁龛；合适的职业；[亦称作 niche market]【商业】有利可图的市场(或形势等)
vt. 放入壁龛
barnacle   英 ['bɑːnək(ə)l]  美 ['bɑrnəkl]  n. [无脊椎] 藤壶；茗荷介；难以摆脱的人；黑雁
spring tide  大潮；涨潮
neap   英 [niːp]  美 [nip]n. 小潮；最低潮 adj. 小潮的 vi. 渐趋向小潮；达小潮的最高点 vt. 由于小潮使搁浅
Within each region of the intertidal zone, one of the barnacle species studied by Connell is the superior competitor. Such asymmetry in competition leading to local competitive exclusion reflects an imbalance in the ecological relationships between two species.

41. Chipmunks Alpine Lodgepole Yellow Pine Least Cold tolerant
Most aggressive
Needs shade
Yellow Pine
aggressive
Least
Heat tolerant
Distribution is partially determined by interspecific competition
Least chipmunk[动] 花栗鼠can occupy from sagebrush山艾树to alpine高山的, 阿尔卑斯山的zone. If yellow pine is removed, least chipmunk will move up.
If least chipchunk is removed, yellow pine chipmunk will not move down.
Lodgpole pine chipmunk is restricted to shade area, is vulnerable to heat. Lodgepole is the most aggressive, may limit the downslope range of alpine chipmunk.
Sierra Nevada, CA

42. 5.4 Habitat productivity can influence competition between plant species
Two hypotheses:
Plants compete more intensively when mineral nutrients are less abundant in the soil (By Grubb and Tilman)
Plants compete more intensively when nutrients are less. High nutrients are less likely to limit plant population; thus the intraspecific competition is weak.
2.Competition is less intense when water and nutrients are less abundant (Grime and Keddy)
Competition for light is more important than competition for nutrients; limit in water and nutrients would limit the population growth to a certain point that individual plants are widely spread and do not compete for light.
Difference between these hypotheses lies in the relative importance placed on belowground and aboveground competition for resources --Light or nutrient. (Debate)
habitat 英 ['hæbɪtæt] 美 ['hæbə'tæt] n. [生态] 栖息地，产地
The difference between the Grubb– Tilman and Grime– Keddy hypothe­ses lies in the relative importance placed on belowground and aboveground competition for resources— that is, for nutrients and light, respectively.

43. Habitat productivity can influence competition between plant species
New England saltmarsh[生态]盐沼community
Upper border set by competition, lower borders set by tolerate the physical: salinity, waterlogging ['wɔ:tə,lɔgiŋ]n. [水文] 涝；水浸涝, 水浸, and low O2
Spartina: cord-grass (s. altermifora: smooth cordgrass; s. patens: saltmeadow cordgrass)
Juncus: black grass
Iva: mesh alder, shrub

44. Habitat productivity can influence competition between plant species
Fertilization alters the outcome of competition by removing nutrient limitation on stress-tolerant plants

45. 5.5 Competition may occur through direct interference
Exploitation开发 : indirectly influencing each other by consuming the same resources (eat same grass by zebras , compete for water uptake by trees, indirectly)
Interference干扰 : direct influencing each other by preventing others to occupy a habit or access resources (birds, bees chase birds and bees, animals release toxic chemicals).
Meadow vole田鼠and mountain vole.
Hummingbirds蜂雀chase other hummingbirds, not to mention不必提及bees and moths, from flowering bushes. Encrusting sponges use poisonous chemicals to overcome other sponge species as they expand to fill open space on rock surfaces. Many shrubs release toxic chemicals into the soil that depress the growth of competitors. Even bac­teria wage chemical warfare with one another to tip the balance of their competitive interactions.
Interference competition is often evident in experi­mental manipulations of competing animal species. For example, two species of voles ( small mouselike rodents of the genus Microtus) are both present in some areas of the Rocky Mountains in North America. In western Montana, the meadow vole ( M. pennsylvanicus) normally lives in wet habitats surrounding ponds and watercourses, whereas the mountain vole ( M. montanus) is restricted to dry habitats. Ecologists believed that this spatial partition­ing resulted from competition between the two species, but the nature of the interaction was not known. How­ever, when meadow voles were experimentally trapped and removed from an area of wet habitat, mountain voles immediately began to move in from surrounding dry hab­itats. This result suggested that meadow voles excluded mountain voles from the wetter areas by direct, aggressive encounters— a case of interspecific territoriality. Interest­ingly, when mountain voles were trapped and removed from a dry habitat that they normally occupied exclusively, meadow voles began to move in. Thus, each species is behaviorally dominant in its preferred habitat, illustrating the principle of home field advantage in rodents.
Meadow草地, 牧场
vole野鼠类, 全胜, 大满贯, 孤注一掷, 什么都干过vole[英] [vəul] [美] [vol]

46. Allelopathy植化相克(chemical competition)
allelopathy   [əli'lɑpəθi; ,æləlɑpəθi]  n. [植] 植化相克；相互影响；远隔酌
clumps  块
shrubby  英 ['ʃrʌbɪ]  美 ['ʃrʌbi] adj. 灌木的；灌木繁茂的；灌木一般的
salvia   英 [‘sælvɪə]  美 [’sælvɪə]  n. 鼠尾草 n. (Salvia)人名；(意、西、罗)萨尔维娅 (女名)，萨尔维亚
mint  英 [mɪnt]  美 [mɪnt] n. 薄荷；[金融] 造币厂，巨款 vt. 铸造，铸币 n. (Mint)人名；(毛里塔)明特
Chemical competition, or allelopathy, has been reported most frequently in terrestrial plants, in which such interac­tions
variety of forms. In most cases, a toxic substance causes injury (- pathy) to other ( allelo-) individu­als directly. For example, black walnut胡桃, 胡桃木( Juglans nigra) trees produce juglone胡桃醌, an aromatic organic compound that inhibits certain enzymes in other plants. As a result, few plant species are capable of germinating and becoming established under black walnut trees. A somewhat differ­ent mechanism of action has been suggested to explain the abundant oils in the leaves and bark of eucalyptus[植]桉树trees of Australia— namely, that they promote frequent fires in the leaf litter, which kill the seedlings of competi­tors ( Figure 16.14).
In shrub habitats in southern California, several spe­cies of sage ( genus Salvia) produce volatile terpenes, a class of organic compounds that includes camphor and gives foods spiced with sage part of their distinctive taste. Terpenes inhibit the growth of other vegetation in the lab­oratory, so investigators proposed an allelopathic function for these compounds in nature. Clumps of shrubby Salvia plants are usually surrounded by bare zones separating the sage from neighboring grassy areas ( Figure 16.15). When observed over long periods, Salvia can be seen to expand into the grassy areas.
Clumps of shrubby Salvia 鼠尾草plants (mint) are usually surrounded by bare zones separating the sage鼠尾草from neighboring grassy areas ( Figure 16.15)
Figure Some plants (eucalyptus) compete by chemical means.

47. Australian ironwood trees
Interference competition can be an important factor in the success of invasive species. For example, Australian ironwood trees ( Casuarina equisetifolia) have been intro­duced into many tropical and subtropical regions of the world, including Florida and the Hawaiian Islands, where they rapidly invade and exclude other vegetation. The nearly complete absence of germination or establishment of native vegetation in soils covered by the needle- like Casuarina leaves suggests an allelopathic effect ( Figure 16.16).
Australian ironwood trees

48. Consumers can influence the outcome of competition
Starfish prey on mussels蚌；贻贝；淡菜
, barnacles, limpets帽贝, and chitons多板类
Remove starfish, what would happen?
Species diversity increase or decrease?
Why?
Several of mussel and barnacle species that were superior competitors in the absence of predation excluded the other species, reducing the overall diversity of the community.

49. Grazing on plant diversity?

50. Predator can influence the outcome of prey competition
Peter Morin, Rutgers
Salamander[动]火蜥蜴
Frog or toad[动]蟾蜍, 癞蛤蟆tadpole [动]蝌蚪
Studies conducted in artificial ponds have shown that predators can reverse the outcome of competition among anuran ( frog and toad) tadpoles. In one experiment con­ducted by Peter Morin of Rutgers University, ponds were supplied with 200 larvae of the spadefoot toad ( Scaphi­opus holbrooki), 300 of the spring peeper ( Hyla crucifer; a frog species), and 300 of the southern toad ( Bufo ter­restris). Each of the ponds, which were identical in all other respects, also received 0, 2, 4, or 8 individuals of the pred­atory broken- striped newt ( Notophthalmus viridescens). In the absence of newt predation, Scaphiopus tadpoles grew rapidly, survived well, and dominated the ponds along with smaller numbers of Bufo; Hyla tadpoles were all but eliminated by competition ( Figure 16.18). How­ever, the newts apparently preferred toad tadpoles, and at higher numbers of predators, survival of both Scaphiopus and Bufo decreased markedly. With fewer toad tadpoles per pond, supplies of food increased, and survival and growth of Hyla tadpoles improved immensely, as did the growth of the surviving Scaphiopus and Bufo tadpoles.

51. Apparent competition（ 似然竞争 ）
In the absence of predator, the population of each prey is regulated by purely intraspecific density-dependent mechanisms
Neither prey species compete, directly or indirectly, with each other
Predator abundance depends on the total abundance of prey
Under these conditions, the combined population abundance of two prey species will support a higher predator density.
Interactions between competing species that are mediated by consumers are often referred to as apparent competition— apparent because the depressing effect of one competitor species on the other resembles exploit­ative or interference competition, but represents the action of a different mechanism. We have seen apparent compe­tition in the interactions between sage and grasses and between mussels and other rocky intertidal organisms: in both cases, consumers determined the competitive bal­ance. The outcome of competition depended less on the ability of competitors to utilize food or other resources efficiently than on their ability to avoid or tolerate their own consumers. In the case of the sage– grass interaction, the shrubs provide protective cover for herbivores that prefer to eat the more nutritious grasses.
中文名称：
似然竞争
英文名称：
apparent competition
定义：
两个物种通过拥有共同捕食者而产生的竞争。其性质与两个物种通过对资源利用所产生的资源利用性竞争类似
如果两种猎物被同一种捕食者所捕食，由于一种猎物数量的增加导致捕食者数量的增加，从而增大了另一种猎物被捕食的风险，从而使两种猎物以共同的捕食者为中介产生相互影响，这种相互影响的结果与资源利用型竞争的结果相类似，称为似然竞争。

52. Apparent competition（ 似然竞争 ）
Combined populations of two prey species support a larger predator population neither can support alone. As a result, two prey populations reduced, gives outward appearance of interspecific competition.
outward appearance 外观；外表
aphid   英 ['eɪfɪd]  n. [昆] 蚜虫
nettle   英 [‘net(ə)l]  美 [’nɛtl]  vt. 剌激；惹恼；用荨麻刺 n. 荨麻 adj. 荨麻科的 [ 过去式 nettled 过去分词 nettled 现在分词 nettling ]
似然竞争
　　如果两种猎物被同一种捕食者所捕食，由于一种猎物数量的增加导致捕食者数量的增加，从而增大了另一种猎物被捕食的风险，从而使两种猎物以共同的捕食者为中介产生相互影响，这种相互影响的结果与资源利用型竞争的结果相类似，称为似然竞争。
Experimental supports:
Nettle荨麻aphid蚜虫, grass aphid and ladybug瓢虫beetle甲虫(Smith and Smith, page 359)
Brought nettle aphid plants to grass aphid plants together suppressed both population, as a results of larger ladybug beetle population.

53. Apparent competition mediated by microbes
Some corals can live with algae (mutualism). Corals can be indirectly harmed by the presence of algae. The health of coral species such as this Pocillopora verrucosa suffers when algae become established nearby. Nature Picture Library/ Alamy.
Corals can be indirectly harmed by the presence of algae

54. Antibiotics can reverse the negative effects of algae on coral growth
Antibiotics can reverse the negative effects of algae on coral growth. Corals were grown in the presence of algae with and without antibiotic treatment. The results suggested that the algae were exerting their negative effects on the health of the corals by supporting microbial overgrowth on their surfaces. After J. E. Smith et al., Ecology Letters 9: 835– 845 ( 2006).

55. Thanks!
2019/2/16