Temporal patterns of biodiversity

Key concepts and theories around succesion 

vegetation- model 

examples- different processes occur 

Sucession is central to ecology as evolution is to biology 
succession crucial to what happens in our environment 

Species change over time (Turnover) SUCCESSION DEFINITION 

Succession is started, directed and redirected by disturbance 
Lots of diff kinds of disturbances - anthrpogenic, natural- natural hazards -
succession is strongly influenced by disturbance 

Incorrectly thougt to progress towards climax (climatic-climax vegetation).

Can't exactly predict what outcomes will be
may be altered by smaller disturbances- fluctutating env,
Outcome depends on all factors influence successional processes 

(A) primary succession- from sterile beginnings 

colonisation of area previously clear from organisms- potential for rapid succession if conditions correct. 

Volcanoes: 3000 active volcanoes, 60-70 erupt annually 
Affecting 500 million people 

Glaciers- 10% earth's surface (90% of that in Greenland and Antarctica) 
75% of glaciers retreeat- global warming 

This creates environment which has potential to act as a platform for primary succession- previous species scraped away by glacier retreating. 

(b) Secondary succession- on previously colonised land after major disturbance 

- landslides, fire, cultivation, land abandonment, wind throw etc

Have propagules (e.g. seeds) and sources of new colonisers
Propagules- don't have total elimination of species- within the space or near it. 

AUTOGENIC: (Species change due to activities of organisms themselves- biotic) 

primarily due to interactions between species which occur in a given space.

e.g. competitive exclusion- better traits/characteristics outcompete, facilitation. 

ALLOGENIC: (Species change due to external non biological factors- abiotic.) 
alo veraaa
climate, microclimate v strong factors - changes physical env rivers likely these processes will be occuring simultaneously lesser degree- always likely allogenic will be playing apart.

AUTOGENIC & ALLOGENIC infuence each other - causal link- to some degree or another 

e.g. climate change, silting of waters etc

(a) early successional species- colonisers 'ruderals' 
ruderals = pioneer species (can look into more detail from book mentioned in second lecture)

Small, fast growing
Produce many small speeds (high dispersal)  - allows it to spread across landscapes widely- wind- feathery seeds- dandelions example.  - Dispersed by birds- seeds ingested by these 

Often no dormancy requirement (germinate if conditions favourable) - plants need dormancy requirement doesnt immediately germinate 
- if eary successional species- won't need dormancy period- little resources to germinate quickly. 

- Often N fixers (lichens, cyanobacteria, dryas) - nitrogen fixers are microbes, microbe association between legumes and certain trees. 
Microbes fix nitrogen turn it into amino acids- benefits early plants
- Association with microbes that can fix N hugely beneficial early soil no nutrients- N needed for amino acids.

- Allocate more energy to reproduction than biomass (growth) - so they can colonise 

(a) short term diversity- number of plant species m2

(b) longer term Diversity 

Glacier retreat at a rate of 0.4km a year.

Creatig a plant-soil successional chronosequence from 1760 to present day. 
Transect allow you to see how species progressed in one day
as glaciers retreated species primary succession

first pioneer communities: 
facilitate plant communty to start to grow- these come on rocks first- windblown- spores- can reproduce quickly, v efficient need little resources- bacterial crust can develop on rocks 

examples: Microbes – bacteria, archaea, fungi, Algae, lichens, liverworts, bryophytes

Leads to... protosoil - concentration of carbon from atmosphere and dissolving organic acids- become available for plants to get stuck in 

r

once protosoil here can facilitate other species Dryas- small rapid growing plants can grow in dry conditionss - light seeds can reproduce v fast 

Dryas (25 years ice free)

woody species - Alder larger seeds- allow them to grow bigger - N fixer association behind ground- diff bateria produce nodules on their roots- benefit - competitive adv over other plants/trees. this specific trait allows them to capitalise on nitrogen- exclude other species- like smaller plants perhaps dryas- soil becomes too wet build up organic material.

Then.... (125 years later)
bigger seeds- outcompete- dominate light- impoverished understory so higher diversity is in the middle again mixture

K is climax community e.g. spruce dominated forest 200 years- one or two species dominating

Seres – successional stages with characteristic vegetation types and associated biota

Different communities through diferents processes sometimes referred to as seres- diff complexities of communities- reduce diversity over time to a forest

each sere (Stage) different heterogeneity 

Example of glacier retreat 

Glaciated in 2006 

A spatial ‘chronosequence’
rock algae protosoil evolving -microbes dissolve algae- release calcium protosoil 
little bits of soil - other plants can adapt- mosses adapted to be tolerant of total drought 

Individual species have characteristic ecological ‘traits’

grazers  like sheep, cows - intefering with processes of succession constraining it allogenic - this selects for certain species which are evolved to grazing. may havv diff env if weren't grazers

Places: Queensland, Australia 

Examples: Monocotyledons, graminoids (grasses, sedges), xerophytes

Characteristics: v salty, windy, unstable env - loads adaptations- 3m deep roots- rapidly grow roots- halocytes and xerophytes can cope with drought and salty conditions 

xerophyte- woody shrubs- building stability 

Plants seek/ seep into rock 
maybe look up poehoehoe lava

humans disturbed landscape- mineral extraction 

tried to plant trees- didnt survive because these were trees which grew in the later stage of succession couldnt grow

graph below 

(a) Pioneer species

Early colonists:

(a)Light seeds, wind dispersed

(b)High seed production

Example: seed mass and successional stage, Glacier Bay

Species          Seed mass (g seed)     Status
Dryas drummondi      97                         early
Alnus crispa              494                        middle
Picea sitchensis        2694                      late

immigration graph

Black algal crusts, Glacier Bay

(Tough, flexible organic mat) 

• Consolidate surface 1-2cm

• Reduce rain impact/particle movement due freeze thaw

• N fixer – supply limiting resource for heterotrophs

V important

Connell and Slayter (1977):

Inhibition model  (autogenic)

• Early arrivals competitively inhibit (e.g. light competition) establishment of later ones
influence sucession by what they do env around them- use resources 

• Spread rapidly (thickets) and monopolise resources until die

Facilitation model

• Succession is a series of sequential invasions, each dependant on site amelioration by earlier colonist. 

through process of succession some species change env facilitates success next species - facilitates spruce

• Species die out since changes in environment better suited for later colonists

'Competitive exclusion'

reaitity is fac & inhb happen simultaneously - facilitaton by coincidence species doesnt want to wipe itself out- but change soil- protosoil- microbes

Example: Nitrogen fixers (soil N accumulation)

77% primary seres have N fixers as dominant vegetationExample: Nitrogen fixers (soil N accumulation)

77% primary seres have N fixers as dominant vegetation

(chemical reaction )

Changes in soil conditions during primary succession at Glacier Bay – driven by alder!

1. Succession is - Species change over time (turnover).
vegetation as model easier- other organisms more difficult - pathogens

2.Succession is started, directed, and redirected by disturbance.
always initial disturbance to create gap - continual influence whether secondary or primary depends propagules - need certain disturbance to be successful 

3.Succession is governed by a range of interacting factors, both biological and abiotic.
facilitation, inhibitation, autogenic, humans putting things in system-