ecological succession

1. ECOLOGICALECOLOGICAL
SUCCESSION:SUCCESSION:
Communities in TransitionCommunities in Transition

2.  Ecological successionEcological succession – gradual change in– gradual change in
species composition of a given areaspecies composition of a given area
 New environmental conditions allow oneNew environmental conditions allow one
group of species in a community to replacegroup of species in a community to replace
(outcompete) other groups(outcompete) other groups
 Usually focused on plants – but animals andUsually focused on plants – but animals and
others followothers follow

3.  Primary successionPrimary succession – gradual establishment– gradual establishment
of biotic communities in lifeless areas whereof biotic communities in lifeless areas where
there is no soil or sedimentthere is no soil or sediment
 Starting from scratchStarting from scratch
 Ex: bare rock exposed by glacier or severeEx: bare rock exposed by glacier or severe
erosion, new lava, abandoned parking loterosion, new lava, abandoned parking lot
 Takes longerTakes longer

5.  Secondary successionSecondary succession – begins in an area– begins in an area
where the natural community has beenwhere the natural community has been
disturbed – soil presentdisturbed – soil present
 Starting in middleStarting in middle

8.  Pioneer speciesPioneer species (early successional species)(early successional species)
– colonizers – 1– colonizers – 1stst
species to arrivespecies to arrive
 Ex: lichens, mossesEx: lichens, mosses
 Mid-successional speciesMid-successional species – next to arrive –– next to arrive –
often need lots of sunlightoften need lots of sunlight
 Ex: herbs, grasses, low shrubsEx: herbs, grasses, low shrubs
 Climax speciesClimax species (late successional species) –(late successional species) –
 Not out-competedNot out-competed
 TemporaryTemporary end of successionend of succession
 Ex: deciduous treesEx: deciduous trees

9. Rate of SuccessionRate of Succession Affected by:Affected by:
 FacilitationFacilitation – one set of species makes area– one set of species makes area
suitable for another set of species and lesssuitable for another set of species and less
suitable for itselfsuitable for itself
•
Ex: lichens build up soilEx: lichens build up soil
 InhibitionInhibition – species hinder growth of other– species hinder growth of other
speciesspecies
•
Ex: pine needles make soil acidicEx: pine needles make soil acidic
 ToleranceTolerance – climax species succeed due to– climax species succeed due to
lack of competitionlack of competition
•
Shade-tolerant plants can survive in forestsShade-tolerant plants can survive in forests
because they do not need as much lightbecause they do not need as much light

10. Pond SuccessionPond Succession

11. Rocky Intertidal SuccessionRocky Intertidal Succession

12. DisturbanceDisturbance
 DisturbanceDisturbance – any event that starts a– any event that starts a
community at an earlier successional stagecommunity at an earlier successional stage

Natural – volcano, glacier, forest fire, floodingNatural – volcano, glacier, forest fire, flooding

Human caused – forest fire, abandoned field,Human caused – forest fire, abandoned field,
pollution, deforestation, overgrazingpollution, deforestation, overgrazing

13.  Is succession good or bad?Is succession good or bad?
 Is disturbance good or bad?Is disturbance good or bad?

14. Intermediate Disturbance HypothesisIntermediate Disturbance Hypothesis
 Highest diversity at an intermediate amountHighest diversity at an intermediate amount
of disturbanceof disturbance

High disturbance – only pioneer species surviveHigh disturbance – only pioneer species survive

Low disturbance – only climax species surviveLow disturbance – only climax species survive

15. Can We Predict the Path ofCan We Predict the Path of
Succession, and is Nature inSuccession, and is Nature in
Balance?Balance?
 The course of succession cannot beThe course of succession cannot be
precisely predictedprecisely predicted
 Previously thought that a stable climaxPreviously thought that a stable climax
community will always be achievedcommunity will always be achieved
 Succession involves species competing forSuccession involves species competing for
enough light, nutrients and space which willenough light, nutrients and space which will
influence it’s trajectoryinfluence it’s trajectory

16. ECOLOGICAL STABILITY ANDECOLOGICAL STABILITY AND
SUSTAINABILITYSUSTAINABILITY
 Living systems maintain some degree ofLiving systems maintain some degree of
stability through constant change in responsestability through constant change in response
to environmental conditions through:to environmental conditions through:

InertiaInertia ((persistencepersistence) – ability of a living system) – ability of a living system
to resist being disturbed or alteredto resist being disturbed or altered

ConstancyConstancy – ability of a living system to keep its– ability of a living system to keep its
numbers within limits imposed by availablenumbers within limits imposed by available
resourcesresources

ResilienceResilience – ability of a living system to bounce– ability of a living system to bounce
back and repair damage after (a not too drastic)back and repair damage after (a not too drastic)
disturbancedisturbance

17. ECOLOGICAL STABILITY ANDECOLOGICAL STABILITY AND
SUSTAINABILITYSUSTAINABILITY
 Having many different species appears toHaving many different species appears to
increase the sustainability of manyincrease the sustainability of many
communitiescommunities
 Human activities are disrupting ecosystemHuman activities are disrupting ecosystem
services that support and sustain all life andservices that support and sustain all life and
all economiesall economies