Bringing the Modern Synthesis into ecology ? (1927-1967)

Bringing the Modern Synthesis into ecology ? (1927-‐1967)

INTORDUCTORY REMARKS: ECOLOGY AND EVOLUTION ??

An ambiguity in the definiAon of ecology

• Ecology: – “science of the struggle for existence” (Haeckel)

– Science of the relaAonships between organisms and their environments “those sciences that

consider organisms in relaCon to their environments and to one another. “ Hutchinson & Deevey 1949

• Def 1: immediately darwinian

• Def 2. non immediately linked to natural selecAon; can be organisms-‐centered or not.

• Ecology/ evoluAon a “simple” relaAon • ecology-‐> selecAve pressure • PopulaAon geneAcs-‐> change in allelic frequency via selecAon and other eovluAonary forces (fitness values reflect selecAve pressure swithin the PG models)

Lynch 2007: nothing in evoluAonary biology makes sense except in the light of populaAon geneAcs

Heterogeneity ecology/evoluAon

• A causal difference: predaAon, compeAAon, etc., ecological interac,on// selecAon mutaAon migraAon driZ as evolu,onary forces

– Ecology : organismic interac,ons consAtute environmental demands

– In an evoluAonary viewpoint they are selec,ve pressures – Natural selecAon is cons,tuted by selecAve pressures

The whole causal picture.

• Causes of selecAon (environmental demands, etc.)

• Fitness values

• Change in gene frequencies, then trait values -‐> evoluAon (adaptaAon, diversity).

Ecology. Compe,,on, preda,on, resources. Development, Physiology…

Popula1on gene1cs. Modeling allelic frequency change as an output of fitnesses, popula,on size, structure etc. Dri@, selec,on, muta,on, migra,on as forces.

Ecology’s dual nature: behavioural ecology // community ecology (level of organisms vs collec1ves (species& popula1ons)

Simple arCculaCon: inverCng variants and invariants

Ecology: varying species (exAncAon, speciaAon, colonizaAon), nonvarying genes

EvoluCon: one focal species populaAon, relaAve environmental constancy (hence species constancy), variaAon of genic frequencies

• Unity of ecology ???

– Community ecology, populaAon ecology, funcAonal ecology, community ecology, biogeography, landcscape ecology, ecosystems ecology, behavioural ecology

– Gradient: ecology with evoluAonary/biology main concepts

Thermodynamic inspired ecology (fctl ecology, ecosystems ecology – Odum)

Merging ecology and evoluAon is sAll a crucial problem; Think “niche construcAon theory”, “ecophylogeneAcs”, etc ((Roughgarden))

Temporal scales

MicroévoluAon PopulaAon geneAcs

macroevoluAon

Behavioural ecology

Community Ecology

FuncAonal Ecology

• One crucial quesAon: explaining diversity.

– In evoluAon: macroevoluAonary quesAon about phylogeny (divergence, etc)

– Hutchinson 1959 – “why are there so many animals” now ? : ecological quesAon

• Ecology aZer the MS: concern with general paferns of bidiversity, and how to mechanisAcally explain them.

The paradox of ecology aRer the MS:

• Struggle for existence = natural selecAon

• No populaAon thinking in ecology

– Even more than “no genes”

The Modern Synthesis Core (Huxley 1951) "Natural selecAon, acAng on

the heritable variaAon provided by the mutaAons and recombinaAon of a Mendelian geneAc consAtuAon, is the main agency of biological evoluAon”

• StarAng point 1927: populaAon biology, life history tables, physiology, animal ecology, plant ecology

• Endpoint 1967: populaAon ecology, funcAonal ecology, community ecology, behavioural ecology, biogeography

StarAng point

• Plant ecology : ‘community’ ecology, issues of succession and assemblage, Clements 1926 vs Gleason, etc.

• Animal ecology: populaAon biology mostly • Lotka Volterra cycles

-‐> Main quesAon: populaAon regulaAon

Landmarks

• Elton 1927 (Animal ecology), 1958 (Invasions) – Studied with Huxley

• Ford, Ecological gene,cs 1964 – Student of Fisher

• Hutchinson 1941, 1957 – Limnologist

• Lack (1947, Finches, 1947, clutch size) – Ornithology; studied with Mayr

• Cold Harbour spring symposium 1957 • Nicholson, Andrewartha, LewonAn, Chify, Dobzhansky, etc.

• McArthur & Wilson Theory of Island Biogeography 1967; Levins, “Fitness in changing environments” papers, 1966

• Mc Arthur, Odum, students of Hutchinson

Episode 0. Elton

• 1927, Animal ecology. – Ecology is " the sociology and economics of animals.”

• Foreword by Huxley (Spitzberg expediAon 1923) – Mayr on Elton

• NoAon of succession, niche, food chain, pyramid of numbers • Journal of animal ecology 1931; • Bureau of animal populaAons, 1932

– Wytham Hill estate, Oxford – 20 years survey – Invasions of rats, etc -‐> Ecology of invasions by animal and plants, 1958 (“geneAc”: 8

occurrences); PaQerns of animal communites, 1966 (16 occurrences) • Emergence of “invasion ecology” and concern with stability

Compare : Elton 1966 – some changes introduced

• 1928-‐1942 – First stages of the Modern Synthesis

• Gause 1932-‐1935:compeAAve exclusion principle experiments on Paramecia

• Gause, GF. 1932. Experimental studies on the struggle for existence. Journal of Experimental Biology 9: 389-‐402.

“ecology” in the MS

• Haldane 1932, Causes of eovlu,on 1 occurrence

• Dobzhansky 1937, Gene,cs and the Origins of species, 3 occurrences

• Huxlery. The modern synthesis (1942), 36 occurrences, many citaAons of Elton

Episode #1. Ecological geneAcs

• Ford 1946, 47.. 1964 – Evaluate natural selecAon in the

wild – Studies on Triphanena comes

moths in England, lepidoptera Polyommatus icarus, Maniola jur,na (with Fisher)in Sicily: polymorphisms mimicry, founder effect..

– Ecology = experimental study of natural selecAon on popuaAons geneAcally defined

– Finding: higher than expected intensiAes of natural selecAon 1 to 20 magnitudes higher)

– Moderate the role of gene,c dri@ – Ford & Fisher 1947 Heredity – these chromosome inversions are in fact subject

to a delicate balance of selecAve intensity.

Episode#2. CompeAAon and density-‐dependence – purng natural selecAon at the center

• Huthcinson & Deevey 1949. Autecology vs synecology

• “All these branches of invesCgaCon, autecology, biocoenology, biodemography, biogeochemistry, may conveniently be regarded as branches of ecology, though they deal with different levels of integraCon or employ different degrees and kinds of abstracCon”

• Most simple abstract models – ecology of homogeneous populaAons, up to 2 species-‐ as a “topical & of enduring interest” way of tackling the problem

•

The paradigmaAc role of populaAon ecology

Parallel with MS

• Elton, C , and Nicholson, M . 1942a. FluctuaAons in numbers of the muskrat (Ondatra zibethica) in Canada. Jour. Anim. Ecol. 11: 96-‐126.

• Lack D. 1947-‐8. The significance of clutch-‐size. Ibis 89, 302–352

• Clutch opAmises the number of offspring

• Darwin’s finches. Cambridge UP. 1946 • Lack’s training. Ornithology. Stays with Mayr 1938

• Hutchinson, G. E. 1941. Ecological aspects of succession in natural populaAons. Amer.Nat. 75: 406-‐418.

CompeAAve exclusion principle

• “The generalizaCon implicit in cases (2) and (3), that two species with the same niche requirements cannot form mixed steady-‐state populaCons in the same region has become one of the chief foundaCons of modern ecology.”. In 1957 (“Concluding remarks” CHS) it’s empirical

• Paradox of the plankton first formulaCon 1941, famous one 1959 “Homage to santa rosalia”)

• “intrinsic” vs “extrinsic” reasons for ecological cycles

» Hutchinson & Deevey p346.

– ReflecAon of debates on the reasons of populaAon regulaAon

– Timescale consideraAons

• Cold Spring Harbour Symosium on populaAons (1957). Controversy on density-‐dependance as an explanans of community composiAon and dynamics

• Anderwartha, Birch. RegulaAon by environemental changes, not compeAAon (food supply almost unlimited)

• Nicholson, Hutchinson, etc : compe,,on is the main driver of biodiversity – > role of natural selecAon

• Issue: compared strength of intraspecific vs interspecific compeAAon

Hutchinson Concluding Remarks 1959

Niche theory (Hutchinson 1959) :

• Hypervolume – property of the species

– like Grinell’s niche rather than Elton’s

• “fundamental” (McArthur) vs “realized” niches

• LimiAng similarity explains coexistence

Niche theory (Hutchinson 1959) :

• Hypervolume – property of the species

– like Grinell’s niche rather than Elton’s

• “fundamental” (McArthur) vs “realized” niches

• LimiAng similarity explains coexistence

• Equilbrium ecology (Comp . Excl) vs non equilibrium (plankton?)

2 remarks

• Natural selecAon plays a crucial role in Hutchinson’s formal model of niche and CEP (decoupling realised and fundamental niches)

• CompeAAve exclusion including paradox of the plancton contrasts with adaptaAonism in ecological geneAcs and Lack

Episode #3. the theoreAcal ecology/populaAon geneAcs parallelism

• McArthur & Wilson 1967. Prospects. A. Island Biogeography

• Wilson’s recollecAon : • “We became friends, and one of our common concerns was the growing

decrepitude of our specialAes (as we saw it), in dismaying con-‐ trast to the newly triumphant emergence of molecular biology. Ecology and evoluAonary biology seemed like the aforemenAoned rhinos and archaic carnivores, surrendering university chairs and grants to the new wave of biologists coming out of the physical sciences. It was clear in the 1960s that their achievements were to be the hallmark of twenAeth-‐ century biology.”

• What can we learn from molecular biology on how to advance our own science? We agreed that the basic problem was that ecology and evoluAonary biology were sAll mostly unrooted. They needed foundaAons from which explanaAons can be developed bofom-‐up. Theory has to work from lower to higher levels of biological organizaAon. Either alone will not do. PopulaAon biology was the disci-‐ pline we thought could serve as base to reinvigorate the theory of ecol-‐ ogy and evoluAonary biology

Explicit connecAon with evoluAon built in the book

• Island biogeography: simple model to account for some paferns in nature (species area-‐curves) with minimal plausible assumpAons

• Methodology: design a model – then compare with the data (hypothesis tesAng) controversies on null models

– (Diamond, Simberloff & O Connro, Gotelli, etc)

• Island biogeography: simple model to account for some paferns in nature (species area-‐curves) with minimal plausible assumpAons

• Methodology: design a model – then compare with the data (hypothesis tesAng) controversies on null models

– Diamond, Simberloff & O’Connor, Gotelli, etc)

– ConnecAon with paleobiology

• Similar formal methods as populaAon geneAcs

• SyntheAc ambiAons: biogeography, geneAcs, evoluAon, ecology

• QuesAons raised: what’s the best colonizator strategies ? – new take on Invasions – colonizaAon is defined in the model first: best increase in populaAon rate

– Concepts: • r and K selecAon • Fitness used as r coefficient • Character displacement (account for geneAc evoluAon)

NoAon of “character displacment” : geneAc undrstanding of eoclogical divergence

Theory of island biogeography

Community ecology

Behavioural ecology

Island-‐mainland models

Strategies, K-‐r selecAon

• McArthur & Wilson p89-‐93 • R is the fitness; character displacement and allelic models in chapter 7 ; relaAon to populaAon geneAcs (cite the end)

• K and r selecAon • ColonizaAon strategies (to understand invasibility)

• 155 – founder effect and mechanism of chapter 4 changed into alleles

• 156 decrease importance of random sampling

• Levins 1962-‐1966 AmNat papers

• Elaborate fitness funcAon that cope with environmental heterogeneity

• Fuels eoclogical informaAon in populaAon egneAcs

• And back

B. Heterogeneous environments

• Thesis 1. one of the main achievment of imporAng MS in ecology was in terms of modeling methodology – especially, used to overcome the divide between plant ecology and animal ecology into theoreAcal ecology

• Thesis 1. one of the main achievment of imporAng MS in ecology was in terms of modeling methodology – especially, used to overcome the divide between plant ecology and animal ecology into theoreAcal ecology

• Thesis 2. No integrated import of MS in ecology (the field is sAll divided, especially into Amescales)

Plant ecology animal ecoloy physiology populaAon biology geography

Ecologicla geneAcs Genes +NS Few “ecological” topics

Behavioural ecology NS, no genes

Biogeography Community ecology NS, genes

Modern Synthesis

Bringing the Modern Synthesis into ecology ? (1927-1967)

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