LSM2251-07 Species Interactions I

8/3/2019 LSM2251-07 Species Interactions I

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Who am I?

A/P: Li Daiqin Specialty: Behavioural Ecology;

Spiders; Biodiversity of Arthropods

Current Research: Animalcommunication; Sexual selection; UV

signalling; Crypsis and mimicry; Spider

sociality; Biomaterials - Spider silk andnanomaterials for structural colour

production

Ultimate Goal: how animals havingsmall brain with few neurons solve the

everyday problems that they face

within their respective environments. Teaching: LSM2251 and LSM4253 Contact details:

Email: [email protected] Tel: 6516 4372 (Office) Office: S2 01-03

TheStraits Times Dec. 25, 2004


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My Favourite-- Jumping spider

Predator-prey relationship

Male-male fighting

Female-male mating


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Species

Interactions (1) -Competition

LSM2251

Ecology and The Environment

A/P Li Daiqin


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Outline

References Background

Classification of species interactions Competition Symbiosis Exploitative interactions Predation Parasitism Herbivory


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References

Molles, M.C. Jr. 2010. Ecology: concepts andapplications, 5th ed. McGraw-Hill.

Byers, J. E. 2000. Competition between two estuarinesnails: implications for invasions of exotic species.Ecology 81: 1225-1239.

Dayan, T. & Simberloff, D. 2005. Ecological andcommunity-wide character displacement: the nextgeneration. Ecology Letters 8: 875-894.

Denno, R.F. & Roderick, G.K. 1992. Density-relateddispersal in planthoppers: effects of interspecificcrowding. Ecology 73: 1323-1334.

Tilman, D. & Cowan, M. 1989. Growth of old field herbson a nitrogen gradient. Functional Ecology 3: 425-438.


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Background- Interactions

Ecology is about NUMBERS and CHANGES inNumbers.

What can affect/change numbers? How can the numbers be changed? How can we study changes in numbers?

Can we predict changes in numbers? How?


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Interactions


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Classification of interactions


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Classification of interactions


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Competition


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Competition

Intraspecific Competition Modes

Competitive Exclusion and Niches Mathematical and Laboratory Models

Lotka-Volterra Competition and Niches

Character Displacement Applications

Competition between invasive and nativespecies


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Modes of competition

Interference: Direct aggressive interaction between

individuals.

Intra-specific: Competition with members of own species.

Inter-specific:

Competition between individuals of twospecies - reduces fitness of both.


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Intra-specific competitionamong plants

Plant growth rates and weights have been found to increasein low density populations.

Tilman and Cowan (1989) grew the grass Sorghastrum nutansat two different densities: low = 7 per plot, and high = 100

per plot.

Found that at low densities S. nutans grew to a large size but not so for those in the high density plots.

Competition for resources (nitrogen) was more intense at highpopulation densities (versus little competition at lowdensities).

This leads to mortality among competing plants. Self-Thinning


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Population density, soil nitrogen, and thesize attained by the grass Sorghastrum

nutans (data from Tilman & Cowan 1989)

Molles 2010.


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Molles 2010.


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Very difficult to show intra-specific competition inherbivorous insects.

Denno and Roderick (1992) demonstrated it withinpopulations of planthopper Prokelesisia marginata.

They thought their results would apply to otherHomoptera due to a combination of limited resources,rapid population growth and their habit of aggregating.

Intra-specific competitionamong planthoppers


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Population density andplanthopperperformance (Data fromDenno & Roderick 1992)

Molles 2010.


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Interference competitionamong terrestrial isopods

Edward Grosholz (1992)used a field experimentwith two treatments: (1)food limitation; and (2)density effects, to

demonstrated it inisopods Porcellio scaber. Supplementing food

had no effect onsurvival.

Survival was lower atthe higher population

density. Due to cannibalism at

the higher density

Molles 2010.


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Laboratory and field studies revealintra-specific competition.

Intra-specific competition for limitedresources plays a key role in slowingpopulation growth at higherdensities.

Interference competition can occur inthe absence of obvious resourcelimitation.

Intra-specific competition:summary


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Niches and inter-specificcompetition

Niche: Environmental factors that influence growth, survival,and reproduction of a species.

Hutchinson (1957) defined niche as: n-dimensionalhypervolume

n equates the number of environmental factors important tosurvival and reproduction of a species.

Gause (1934) came up with the Principle of CompetitiveExclusion

Two species with identical niches cannot coexist indefinitely One will be a better competitor and thus have higher fitness and

eventually exclude the other. Thus, coexisting species will have different niches.


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Niches and inter-specificcompetition

Fundamental niche the ideal hypervolume;the physical conditions under which a speciesmight live, in the absence of interactions withother species.

Realized niche includes interactions such ascompetition that may restrict environmentswhere a species may live.

Example: feeding biology as niches of Darwinfinches - feeding niches Availability of suitable food affects the survival and

reproduction


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The Galpagos Archipelago and IslaDaphne Major home of Darwins

finches


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Petren et al. 2005. Mol. Ecol. 14: 2943-2957


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Feeding niches of Galapagos ground finches

Grant (1986) found

differences in beak sizeamong ground finches

translates directly intodiet.

Size of seeds eaten canbe estimated by

measuring beak depths.Individuals with deepestbeaks fed on hardestseeds.

After the 1977 drought,the remaining seedswere very hard. Thus,

mortality was mostheavy in birds with

smaller beaks (becausethey couldnt crack thehard seeds).

Molles 2010


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Famous Darwins finches themedium ground finch Geospiza fortis


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Beak size within speciesGeospiza fortis

Boag & Grant. 1984. Biol. J. Linn.Soc. 22: 243-287


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Relationship between hardness ofseeds eaten and beak depth

With thepopulation,individuals with

the deepest beaksfed on the hardestseeds, whileindividual with theshallowest beaks

fed on the softestseeds.

Molles 2010.


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Seed depletion by the medium groundfinch, Geospiza fortis, and average seedhardness (Grand 1986)

As seeds are depleted,finches eat the smallestand softest seeds first,leaving the largest andtoughest seeds.

Following drought(selection) not only areseeds in short supply,the remaining seeds arealso tougher to crack.

Mortality fell mostheavily on smallerfinches with smallerbeaks.

Molles 2010.


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Selection (drought) for largeindividuals with large beak size

Boag & Grant. 1984. Biol. J. Linn.Soc. 22: 243-287


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Feeding niches of ground finches:summary

Food is the major determinant of survival andreproduction among ground finches, thus beaksize gives a good picture of Darwin finchesniches.

However, the niches of other organisms aredetermined by entirely different environmentalfactors.


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Mathematical and LaboratoryModels

Mathematical and laboratory modelsprovide a theoretical foundation forstudying inter-specific competition innature

Metz(1972) summarized models: Abstractions and simplifications, not facsimiles

of nature.

Man-made construct; partly empirical andpartly deductive.

Used to provide insights into naturalphenomena.


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Modelling inter-specific competition:Lotka-Volterra competition model

Logistic model for population growth of asingle species:

dN/dt = rmaxN ((K-N) / K)

Population growth of each species: dN1 / dt = rmax1N1 ((K1-N1) / K1)

dN2 / dt = rmax2N2 ((K2-N2) / K2)

Population growth slows as N increases as theratio of numbers to carry capacity, either N1/K1or N2/K2.


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Effect of inter-specific competition onpopulation growth of each species: dN1 / dt = rmax1N1 ((K1-N1-12N2) / K1) dN2 / dt = rmax2N2 ((K2-N2- 21N1) / K2)

12: Effect of individual of species 2 on rate ofpopulation growth of species 1.

21: Effect of individual of species 1 on rate ofpopulation growth of species 2.

12 and 21 are called competition coefficients. 12 > 1, then the competitive effect of an individual of

species 2 on the population growth of species 1 isgreater than that of an individual of species 1.

12 < 1, then the competitive effect of an individual ofspecies 2 on the population growth of species 1 is lessthan that of an individual of species 1.


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In general, LV predicts coexistence of twospecies when, for both species, inter-specific competition is weaker than intra-specific competition.

Otherwise, one species is predicted toeventually exclude the other.



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Predict population growth for the twospecies will stop when:

N1=K 1- 12 N2 and N2 = K 2- 21 N1 Zero Growth Isoclines

Above: Population decreasing Below: Population increasing

Coexistence of two species is only possible whenisoclines cross.



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Molles 2010.


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Paramecia lab experiments

Gause (1934) used laboratory experiments totest the major predictions of LV competitionmodel.

He demonstrated resource limitation withfreshwater, ciliated protozans Parameciumcaudatum and Paramecium aurelia in presence oftwo different concentrations of the bacterium

Bacillus pyocyaneus. When grown alone, carrying capacity determined by

intra-specific competition. When grown together, P. caudatum quickly declined.

Reduced resource supplies increased competition.


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Paramecia lab experiments

Molles 2010.

Would one of the two speciesdrive the other to extinction ifgrown together in microcosms

where they were forced tocompete with each other for a

limited food supply.

When grow alone, both speciesdid well, the carrying capacityis determined by intra-specific

competition.

When grown together, P.aurelia survived, while thepopulation ofP. caudatum

quickly declined. Competitionexclusion results fromcompetition for limited foodsupply.


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Flour beetle experiments

Tribolium beetles infest stored grainproducts.

Park (1954) studied inter-specific competitionbetween T. confusum and T. castaneum undervaried environmental conditions.


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When grown separately inhot-wet environments, bothspecies did well.

When grown together in hot-wet environments, Triboliumcastaneum usually excludesT. confusum.

In contrast, when growntogether in cool-dryconditions, T. confusumusually excludes T.castaneum.

How can we interpret theresults of these laboratoryexperiments in terms of theeffects of competition onthese species niches?


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Competition and niches

Competition can have short-termecological effects on the niches of speciesby restricting them to their realizedniches. But if competitive interactions are strong and

pervasive enough, they may produce anevolutionary response in the competitorpopulation. Changes fundamental niche (fuller range of

environments in the absence of inter-specificcompetition).


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Niches and competition among plants

Tansley (1917) suggested inter-specificcompetition restricts realized niche of each of twospecies of bedstraw (Galium spp.) to a narrowerrange of soil types.

One species is usually found on acidic soils, the other onlimestone soils.

When grown together, both showed clear competitivedominance on their own soil types.

But both species can grow well on either soil type ifthey are not planted together.


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Figure 13_17


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Connell (1961) discovered inter-specific competition in barnacles.

Balanus plays a role indetermining lower limit of

Chthamalus within intertidal

zone.

Chthamalus will grow in themiddle intertidal zone ifBalanus

are removed. Balanus crowd out

Chthamalus.

Balanus are not found in theupper intertidal as it cannot

withstand the high levels of

desiccation.

Niche overlap and competition between barnacles

Molles, M.C. Jr. 2010. Ecology: concepts and applications, 5th ed. McGraw-Hill.


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Character displacementBecause degree of competition is assumed to depend upon degree of niche

overlap, inter-specific competition has been predicted to lead to directional

selection for reduced niche overlap.

Molles, M.C. Jr. 2010. Ecology: concepts and applications, 5th ed. McGraw-Hill.


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Character displacement

Taper and Case: Necessary criteria: Morphological differences between sympatric

species are statistically greater thandifferences between allopatric populations.

Differences between sympatric and allopatricpopulations have genetic basis.

Differences between sympatric and allopatricpopulations evolved in place, and are notderived from different founder groups alreadydiffering in the character.


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Character displacement

Variation in the character (e.g. beak size) musthave a known effect on use of resources (e.g.,seed sizes).

Must be demonstrated competition for theresource (e.g., food) and competition must bedirectly correlated with character similarity(e.g., overlap in beak size).

Differences in character cannot be explainedby differences in resources available to each of

the populations.


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Applications: competition betweennative and invasive species

Species invasion is one of the most significantcontemporary environmental problems.

What are the mechanisms by which allow invasivespecies to invade communities of native species?

Superior competition ability.Byers (2000) used field experiments to explore

the ecological relationships of native (Cerithideacalifornica) and an invasive species of mud snail(Batillaria attramentaria) in North America.

Density effects of native and invasive


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Density effects of native and invasivesnails on the abundance of diatoms andgrowth rate resource competition

Both reduce diatom density, but nodifferences in the effect on diatomabundance

Invasive snails grow faster than native snailsat all densities, showing potential competitionbetween native and invasive species


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Competition: summary

Three types of competition.Laboratory and field studies reveal intra-specific

competition.

Two species with identical niches cannot coexistindefinitely, thus coexisting species will havedifferent niches.

Mathematical and laboratory models provide atheoretical foundation for studying inter-specificcompetition

Competition can have significant ecological andevolutionary effects on the niches of species.


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LSM2251-07 Species Interactions I

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