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Chapter 8 Competition and Coexistence 群體生態學Synecology: community ecology 以生物組織水準來分 1. 個體生態學Autecology: Life history, adaptation 2. 種群生態學Population ecology 3. 群體生態學Synecology: community ecology 4. 生態系統生態學Ecosystem ecology Outline • Forms of competition: Interspecific and intraspecific • Intraspecific competition – Common in nature – Described by the 3/2 thinning law Outline • Interspecific competition – Common in nature – Outcome affected by • Physical environment • Other species Outline • Competition – Exists among 55-75% of the species – Mechanism: over use of the same resource Outline • Mathematical models, called LotkaVolterra models, predict four outcomes of competition – – – – One species eliminated The other species is eliminated Both species coexist Either species is eliminated, depending on starting conditions Outline • Competing species can coexist through partitioning of resources Community： 群體，群聚，群落 • 群落是居住的相當靠近且有交互作用可 能物種集合 • 生物在自然界依循一定的規律而集合成 群落 • 特定空間或特定生境下若干生物種群有 規律的組合 • 彼此間或與環境間互相作用與影響，具 有一定形態結構與營養結構，執行一定 功能 Community群落 A group of populations of plants and animals in a given place; used in a broad sense to refer to ecological units of various sizes and degrees of integration. 福壽螺為什麼要把卵產在枝幹上？ Three types of Community： 群體，群聚，群落 1. Abstract community抽象群聚：心裡想像的 特殊形式群聚，事實上並不存在，如沙漠 ，草原群聚 2. Associational community聯合群聚：過渡形 式的生物群聚，如森林，草原，池塘 3. Concrete community具體群聚：可直接觀察 的特殊區域 （1） Global community全球性群聚：陸地terrestrial ，海洋oceanic （2） Regional community區域性群聚=Biotic province 生物領域（根據溫度、雨量等不同、將全世界分 成：冷溫熱三區（下含16個生物相Biome) 群落（體）生態學Synecology: community ecology Competition Predation Community structure Species diversity succession 群落的基本特徵 1. 2. 3. 4. 5. 6. 7. 具有一定種類組成 不同物種間相互影響 形成群落環境 具有一定結構 一定的動態形式 一定的分布範圍 群落的邊界特徵 Chapt. 08 馬拉威湖慈鯛科的適應性演化 #14 Interactions among species: 種間的關係 (一)競爭competition (二)互惠mutualism (三)共棲commensalism (四)共生和附生protocooperation (五)寄生parasitism (六)捕食predation The evolution of interactions among species(I) • Mimicry擬態：從模仿其他物種的外表 上獲得好處的現象。 • Bastesian mimicry貝氏擬態：無毒害的物種藉 由模擬有害物種而獲利的情形。 • Mullerian mimicry木氏擬態: 兩種不同物種之間 的擬態。 • Aggressive mimicry攻擊性擬態： 有毒的種類模 擬無毒的種類，以提升其偽裝效果，增加掠食 成功率。 The evolution of interactions among species(II) • Coevolution共同演化：例如植物和昆蟲 間的共同演化。 • Parasitism寄生: • Mutualism互利共生： • Competition競爭： • Predator-prey掠食者與獵物： • Herbivore-plant草食性動物與植物： 血桐的蜜 Why are community interactions important? • 群體是居住的相當靠近且有交互作用可能 物種集合 • 烏頭翁和白頭翁混居的結果會如何？ • 草原上只有羚羊而沒有獅子，結果會如何 ？ • 如果沒有蝴蝶或蜜蜂，開花植物的世界將 會如何？ 動物可以消滅植物嗎？ 這麼多的小螃蟹都可以長大嗎？ 這些小鰻苗為什麼要力爭上游？ 群 聚 的 利 己 主 義 與 交 互 作 用 假 設 的 檢 日本禿頭鯊和蝦苗 小蘭嶼火山口 在寄主與寄生系統中快速的族群改變 一群共域棲息蜥蜴的資源分配現象 Niche: 生態龕、生態位、生態區位 . The sum total of a population’s use of the biotic and abiotic resources of its environment; the role a population plays in its environment.一個生物在它所生存的環境中 ，對於生物性與非生物性資源利用的總和。 . The niche is a property of the species or population; it is defined functionally or in terms of the species’ tolerance limits 影響生物的因子 • 非生態因子Non-ecological factors: – 對有機體生活無明顯影響的環境因子。 • 生態因子Ecological Factors – 生物性因子Biotic factors （一）共生 （二）天敵 （三）競爭 （四）抑制 （五）傳播 – 非生物性因子 Abiotic factors 山櫻花為什麼先開花後長葉子？ 自然競爭的實驗性證據 實驗室中草履蟲族群的競爭 實驗室中掠食者和獵物之間的動態關係 邏輯模型所預測的族群成長情形 指數成長和對數成長的比較 Lotka-Volterra model: • 獵物按指數增長，捕食者沒有獵物時按 指數減少的世代連續模型。 • dN1/dt = r1N1[(K1-N1)/K1] • dN2/dt = r2N2[(K2-N2)/K2] R = population growth rate N = population size K =carrying capacity Lotka-Volterra model:獨立時 • （1）獵物prey dN/dt = r1N N = prey density t = time R1 = population growth rate • （2）捕食者predator dP/dt = -r2P N = predator density t = time R1 = population mortality rate Species Interactions • Types of competition Intraspecific competition between members of the same species. Interspecific competition between different species. Aphid sucking leaf sap Caterpillar chewing leaf Species Interactions • Summary of biotic interactions (Table 8.1) Species Interactions • Summary of biotic interactions (cont.) – Herbivory, predation, parasitism • Positive for one population • Negative for the other population – Batesian mimicry • Mimicry of a non-palatable species by a palatable one Species Interactions – Batesian mimicry (cont.). • Positive for one population • Negative for the other population – Amensalism • One-sided competition • One species had a negative effect on another, but the reverse is not true. Species Interactions – Neutralism • Coexistence of noninteracting species • Probably rare – Mutualism and commensalisms • Less common • Symbiotic relationships Species Interactions – Mutualism and commensalisms (cont). • Species are intimately associated with one another • Both species may NOT benefit from relationship • Not harmful, as is the case with parasitism – Competition • Negative effect for both species Species Interactions • Types of competition (cont.). – Interspecific – Intraspecific • Characterizing competition – Resource competition • Organisms compete for a limiting resource Species Interactions • Characterizing competition (cont.). – Interference competition • Individuals harm one another directly by physical force Intraspecific Competition • Quantifying competition in plants vs. animals – For plants, expressed as change in biomass – For animals, expressed as change in numbers – Plants can not escape competition Intraspecific Competition • Quantifying competition in plants vs. animals (cont.). – Animals can move away from competition – Yoda (1963) • Quantify competition between plants • Yoda's Law or self-thinning rule; 3/2 power rule Intraspecific Competition – Yoda (1963) (cont.). • Describes the increase in biomass of individual plants as the number of plant competitors decrease. • Log w = -3/2 (log N) + log c • w = mean plant weight • N = plant density • C = constant Intraspecific Competition – Yoda (1963) (cont.). • w = cN3/2 Interspecific Competition: Laboratory Experiments • Field experiments – Organisms can interact with all other organisms – Natural variations in the abiotic environment is factored in Interspecific Competition: Laboratory Experiments • Laboratory experiments – All important factors can be controlled – Vary important factors systematically Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments – Tribolium castaneum (Figure 8.4a) and Tribolium confusum Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Large colonies of beetles can be grown in small containers – Large number of replications Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Observed changes in population sizes over two-three years Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Waited until one species became extinct Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Cultures were infested with a parasite Adelina Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – T. confusum won 89% of the time Without the parasite, no clear winner Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Microclimate effects (Figure 8.4) 100 90 Percent wins 80 70 60 50 40 30 20 10 0 Hot Temperate Wet T. castaneum T. confusum Cold Hot Temperate Dry Cold Interspecific Competition: Laboratory Experiments – Microclimate effects (cont.). • T. confusum did better in dry environments • T. castaneum did better in moist environments Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Mechanism of competition - predation of eggs Interspecific Competition: Laboratory Experiments • Thomas Park competition experiments (cont). – Predatory tendencies varied with different strains • Figure 8.5 100 90 80 Perfect wins 70 60 50 40 30 20 10 0 bI bII bIII bIV CI bI bII bIII bIV CII bI bII bIII bIV bI bII CIII Genetic strain of beetle T.castaneum T.confusum bIII bIV CIV Interspecific Competition: Laboratory Experiments • Interspecific competition: Natural systems – Assessing the importance of competition • Remove species A and measure the response of species B Interspecific Competition: Laboratory Experiments – Assessing the importance of competition (cont.). • Difficult to do outside of laboratory – Migration problems – Krebs or Cage effect Interspecific Competition: Laboratory Experiments – Assessing the importance of competition (cont.). • Examples in nature – Parasitic wasps – Figure 8.6 (a) Orange County 100 A. chrysomphali displaced by A. lagnanensis on oranges 80 60 40 20 (b) Santa Barbara (mild) Percent of individuals 0 (c) San Fernando Valley (hot) 100 No competitive displacement A. chrysomphali 80 A. lagnanensis A. melinus 60 40 20 0 100 80 Competitive displacement of A. lagnanensis 60 40 20 0 1 2 Year 3 Interspecific Competition: Laboratory Experiments • Examples in nature (cont.). – Used to control scale pest – Climate can alter competitive The Frequency of Competition • Joe Connell (1983) – Competition was found in 55% of 215 species surveyed – Figure 8.7 Resource utilization b) Resource supply a) A B C D Ant Beetle Mouse Bird A Ant Resource spectrum, (for example grain size) C Mouse AB BC CD AB AC AD BC BD CD The Frequency of Competition • Joe Connell (1983) (cont.). – Effects of number of competing species • Single pairs: competition was almost always reported (90%) The Frequency of Competition – Effects of number of competing species (cont.). • Multiple species, competition was reported in 50% of the studies The Frequency of Competition • Joe Connell (1983) (cont.). – Differing opinions - Schoener (1983) The Frequency of Competition • Common flaws of studies – Positive results tend to be more readily The Frequency of Competition • Common flaws of studies (cont.). – Scientists do not study systems at random may work in systems where competition is more likely to occur The Frequency of Competition • Failure to reveal the true importance of competition in evolution and ecological time – Most organisms have evolved to escape competition and lack of fitness it may confer The Frequency of Competition • Failure to reveal the true importance of competition (cont.). – Competition may only occur infrequently and in years where resources are scarce The Frequency of Competition • Patterns of competition – Figure 8.8 Freshwater Marine Habitat Terrestrial Vertebrates Invertebrates Taxa Carnivores Herbivores Plants 70 60 50 40 30 20 Percent competition 10 0 The Frequency of Competition • Mechanisms of competition (Schoener, 1963) – Table 8.2 The Frequency of Competition • Mechanisms of competition (Schoener, 1963) (cont.). – Consumptive or exploitative – Preemtive – Overgrowth The Frequency of Competition • Mechanisms of competition (Schoener, 1963) (cont.). – Chemical • Allelopathy – Territorial The Frequency of Competition • Mechanisms of competition (Schoener, 1963) (cont.). – Encounter The Frequency of Competition • Differing views of competition – Gurevitch et al. 1992 • Found no differences in competition between different habitat types but did find filter feeders and herbivores competed more than carnivores or plants. The Frequency of Competition • Differing views of competition (cont.). – Grime 1979 • Competition unimportant for plants in unproductive environments The Frequency of Competition • Differing views of competition (cont.). – Tilman 1988 • Competition occurs across all productivity gradients Modeling Competition • Based on logistic equations for population growth • Growth equations for two populations coexisting independently – For species 1; dN1 /dt = r1N1 [(K1- N1) / K1] Modeling Competition • Growth equations for two populations coexisting independently (cont.). – For species 1; dN2 /dt = r2N2 [(K2 - N2) / K2] • r = per capita rate of population growth Modeling Competition – For species 1; dN2 /dt = r2N2 [(K2 - N2) / K2] (cont.). • N = population size • K = carrying capacity • Subscripts refer to species Modeling Competition • Populations that compete – Conversion factor that quantifies the per capita competitive effect of one species on another – For species 1; dN1 /dt = r1N1 [(K1 - N1 - aN2) / K1] Modeling Competition • Populations that compete (cont.). – For species 1; dN2/dt = r2N2 [(K2 - N2 - bN1)/ K2] • a = per capita competitive effect of species 2 on species 1 • b = per capita competitive effect of species 1 on species 2 Modeling Competition • Populations that compete (cont.). – dN1 /dt = 0: zero-growth isocline – Four possible outcomes • Figure 8.12 N2 k1 a Species 2 eliminated k1 k a > 2 k2 <k1 dN 2 =0 dt b k2 dN 1 dt 0 N2 k2 k2 dN 1 =0 dt k1 N1 0 b Either species 1 or species 2 eliminated N2 k1 a k2 k1 a k2 Species 1 eliminated dN 1 =0 dt a =0 k1 N2 k1 k2 N1 b Both species coexist dN 1 =0 dt dN 1 =0 dt 0 k2 k1 N1 0 1. b Region of increase of N1 only 2. Region of increase of N2 only 3. Region of increase of N1 and N2 k1 k2 b N1 Modeling Competition • Test of equations – Figure 8.13 1.8 K1 = 13.0 Pure populations Pure populations 1.0 8 6 Mixed populations 4 2 10 Volume of yeast (b) Saccharomyces 20 30 40 50 60 0.2 Alcohol concentration (%) (a) 14 12 10 70 Volume of yeast, pure populations Volume of yeast, mixed populations Alcohol concentration, pure populations Pure populations K2 = 5.8 6 5 4 3 2 Mixed populations 1 Schizosaccharomyces 20 40 60 80 100 120 140 Time (hr) Modeling Competition • Deficiencies – The maximal rate of increase, the competition coefficients, and the carrying capacity are all assumed to be constant – There are no time lags Modeling Competition • Deficiencies (cont.). – Field tests of these equations have rarely been performed – Laboratory tests have shown divergence • Figure 8.14 N1 increase K1/a N2 increase N1 and N 2 increase K2 Equilibrium N2 K1 N1 K 2/b Modeling Competition • Deficiencies (cont.). – Mechanisms that drive competition are not specified • R* - Tilman (1982, 1987) alternative – Need to know the dependence of an organism's growth on the availability of resources – Figure 8.15 Species A Growth Loss 0 R*A 10 Species B Growth Loss 0 R*B 10 Resource level (R) 100 Species A Species B R* 0 Time Resource level (R) (c) Growth or loss rate Growth or loss rate (b) Population size (a) R*B 0 Coexistence of Species • Niche – Grinnell (1918): a subdivision of a habitat that contains an organism's' dietary needs, its temperature, moisture, pH, and other requirements Coexistence of Species • Niche (cont.). – Elton (1927) and Hutchinson (1958): an organism's role within the community • Gause: two species with similar requirements could not live together in the same place Coexistence of Species • Hardin (1960): Gause's principle, known as competitive exclusion principle, where direct competitors cannot coexist Coexistence of Species • David Lack: Competition and coexistence in about 40 pairs of birds, mediated by habitat segregation. – Figure 8.16 10 0 By feeding habitat By geography Number of species pairs Segregating across different axes By habitat 20 Coexistence of Species • Examples of coexistence – Darwin's finches on the Galaapagos – Terns on Christmas Island (Ashmole 1968) Coexistence of Species • Ranks for resource partitioning (Schoener 1974) – Macrohabitat (55%) – Food type (40%) – Time of day or year (5%) Coexistence of Species • Hutchinson (1959) – Seminal paper, "Homage to Santa Rosalia, or why are there so many kinds of animals?" – Examined size differences for • Sympatric species (species occurring together) Coexistence of Species • Hutchinson (1959) (cont.). – Examined size differences for (cont.). • Allopatric species (occurring alone) • Table 8.3 Coexistence of Species – Examined size differences for (cont.). • Hutchinson's ratio, 1.3 – Criticism of Hutchinson • Studies that supported Hutchinson - inappropriate statistics Coexistence of Species – Criticism of Hutchinson (cont.). • Further tests showed no differences between species than would occur by chance alone. • Size-ratio differences could have evolved for other reasons Coexistence of Species – Criticism of Hutchinson (cont.). • Biological significance cannot always be attached to ratios, particularly to structures not used to gather food. Figure 8.17 Coexistence of Species • Hutchinson (1959) (cont.). – Support of Hutchinson – Figure 8.18 d/w analysis for separation on continuous resource sets Coexistence of Species – Figure 8.18 d/w analysis for separation on continuous resource sets (cont.). • Figure 8.19 Resource availability, K Resource utilization d A B w Resource spectrum (x) C Coexistence of Species • Figure 8.19 (cont.). – d=distance between maxima – w = measure of spread • Figure 8.20 a1 Second niche dimension b1 a a a2 c1 b2 b b c c c2 A A1 B1 B C C1 A 2 B2 First niche dimension C2 Coexistence of Species • Hutchinson (1959) (cont.). – Discontinuous resource distribution • Figure 8.21 Leaf pairs N2 50 1 N1 2 20 50 3 20 50 4 20 5 20 6 20 7 20 Distribution of insect A Distribution of insect B 8 P.S. = 0 + 0.166 + 0.166 + 0 + 0 + 0 + 0 + 0 = 0.333 Coexistence of Species – Discontinuous resource distribution (cont.). • Figure 8.22 0.4 Species A Proportion 0.3 0.2 Species B 0.1 0 1 2 3 4 Resource set 5 6 7 8 Coexistence of Species – Discontinuous resource distribution (cont.). • Niche overlap between two insect species that feed on a shrub – Measured quantity » PS = Spi » PS = proportional similarity » S = sum of all units, 1 to n, in resource set Coexistence of Species – Measured quantity (cont.). » pi = proportion of least abundant member of pair » PS < 0.70 indicates coexistence for single resource » PS > 0.70 indicates competitive exclusion for single resource Coexistence of Species – Measured quantity (cont.). » Proportional similarity indices for two or more resources can be combined •Multiply separate PS values to determine overall PS value •Coexistence for two resources – 0.7 x 0.7 = 0.49 or less Applied Ecology • Is the release of multiple species of biological control agents beneficial? – Control of pests in agriculture is of paramount importance Applied Ecology • Is the release of multiple species of biological control agents beneficial? (cont.). – Biological control is seen as a preferable alternative to chemical control Applied Ecology – Biological control viewed by some • Release a variety of enemies against a pest • Observe which enemy does the best job Applied Ecology – Biological control viewed by some (cont.). • Is this the best strategy? – Intensive competition for the prey leads to lower effectiveness of the biological agents – Greater population establishment rate with fewer enemy species (Figure 1 for Box 1) Applied Ecology • Is this the best strategy? (cont.). – Establishment rate of single-species releases were significantly greater than the simultaneous release of two or more species (76% vs. 50%) Summary • Competition may be interspecific or intraspecific • Competition may be viewed as resource competition or interference competition Summary • Intraspecific competition between plants may be described by the 3/2 self-thinning rule Summary • Outcome of competition can be influenced by – Environmental conditions – The presence or absence of natural enemies Summary • Outcome of competition can be influenced by (cont.). – The genetic strain of the competitors involved Summary • Experimental studies show that in nature competition occurs between different types of organisms over a broad scale – Such studies focused on exotics and generalizations to natural ecosystems are questionable Summary • Experimental studies show that in nature competition occurs (cont.). – Competition between exotics and native species • Serious consequences for natural ecosystems Summary • Frequency of competition – 55% to 75% of species involved – Competition is often asymmetric • Six mechanisms of competition – Consumptive – Preemptive Summary • Six mechanisms of competition (cont.). – – – – Overgrowth Chemical Territorial Encounter Summary • Lotka-Volterra model: early competition model – Two species interaction – Four possible outcomes • Species 1 becomes extinct • Species 2 becomes extinct Summary – Four possible outcomes (cont.). • Either species 1 or species 2 becomes extinct based on starting conditions • Coexistence Summary • Lotka-Volterra model: early competition model (cont.). – Competition is minimized and species can coexist if they use different resources • Hutchinson's 1:1.3 ratio Summary – Competition is minimized and species can coexist if they use different resources (cont.). • d/w values greater than unity • Proportional similarity values no greater than 70% Discussion Question #1 • Which type of competition would you expect to be more important in nature? Discussion Question #2 • Much native vegetation in the Florida Everglades is being lost. Could this be due to climate change or the influence of exotic invaders? Design an experiment. Discussion Question #3 • In the above question, how could you determine the mechanism of competition? How could you differentiate among competition for light, water, or nutrients? Discussion Question #4 • In trying to understand how species compete, what advantages are there in field observations, field experiments, laboratory experiments, and mathematical models? Discussion Question #5 • Using fully labeled graphs, explain the LotkaVolterra approach to competition theory. What predictive power does the Lotka-Volterra model have? How is Tilman's R* concept an improvement? What other improvements might you suggest?
