1

Colonization of a site:

dispersal adaptations

requirements

sequence

r and K strategy

Consequences

More examples

Dispersal and colonization of habitats

Example

Location: present

Indonesia, island of

Krakatoa

The explosion destroyed completely life on the volcano and adjacent

islands.

A new cone formed and its ecological development was monitored, with

decent ecological surveys made as early as 1897.

The 1883 eruption

ejected more than 25

cubic kilometers of

rock, ash, and pumice

Example

Only fraction of

the surface is

alive …

Colonization

and

development of

communities

was interrupted

several times

2

Krakatoa (Krakatau) – dispersal types

After Whittaker et al. 1997

Ridley„s dispersal classification on the then known floras on

Krakatau (up to 1919 only), Christmas Island and Cocos-

Keeling

Dispersal type Krakatau

Christmas Cocos

Sea borne 60 44 17

Wind 34 9 0

Berry or drupe 34 36 0

Adhesive 9 15 5

Mud on birds 3 0 0

Doubtful 4 7 0

Total 144 129 22

Pteridophyta 48 25 0

Timing

Hawaii (more isolated):

• one plant species every 30 000 years,

• one land snail every 200 000 years and

• one bird species every 350000 years These estimates are based on the average age of the

islands being 5 million years

The colonization of the

newly built Krakatoa

island by plants &

animals took 50 years;

First:

Timing of

arrival

Category 1897 1924 1989

Sea dispersed

flowering plants

23 53 59

Animal dispersed

flowering plants

2 48 110

Wind dispersed

flowering plants

14 48 75

Ferns (all wind-

dispersed)

13 51 81

A shift from “sea” to “animals”

3

5-20 years

Ferns appear to dominate first settlers. Why?

Empty space: primary sites Primary sites –

where no prior

communities

existed

Empty space: secondary sites Secondary

sites – where

new „space‟

opens at the

partial

expense of an

old community

Implications: modified physical habitat, propagules

New

secondary site

Primary sites – who arrives first?

- transient animals

- seeds or spores carried by wind or

transient animals

- small seeds before large ones

Two steps: arrival and settlement

What are typical properties of early arrivals?

- small

- resistant to high temperature, low humidity

- adapted to fast or delayed germination

- adapted to transport (burs, wings, hairs)

- require light, i.e., no shade from other plants

4

Dispersal adaptations

Fur Wind Consumer

Wate

r

Non-consumers Hoarders

Ocean

currents

Requirements

Ability to survive travel in a physically

demanding environment (rock, air, ocean, dry

and hot mineral soil)

Ability to survive germination or birth in the

above

Ability to reach reproductive maturity, or

reproduce vegetatively, or parthenogenetically

(animals)

High reproductive rates, colonial nature

(examples ….?) e.g., beach creepers (vine like

plants)

Differential performance

Who (plants)

stays on site?

Plant Characteristic Value

Photosynthesis light saturation efficiency at low light photosynthetic rates

High

Low

High

Water use efficiency transpiration rates

high

Seeds number size dispersal distance viability induced dormancy

High Small Large Long common

Root/shoot ratio low

Mature size small

Growth rate high

5

r and K strategy

Time (t)

N

rNdt

dN

K

NKrN

dt

dN

Recall:

r = net rate of N increase (speed). Thus:

K = carrying capacity (~max N). Thus, if there is a limit:

Invading plants grow quickly, and make lots of seeds ( “r” strategists). “K” strategists focusing their energy and resources on growth and long-term survival (usually come in later in the settlement of new habitat).

From this:

If N is small, a species must grow fast; if N is near K, it should keep it without large fluctuations

Pioneer communities

Mature communities

Dispersal limitation: limitation of distribution or abundance

because of either constraints on dispersal or inadequate

production of dispersing individuals.

Recruitment limitation: limitation of distribution or abundance because

of either constraints on survival of individuals that arrive or were born at

a site (local filter). How would we demonstrate it empirically?

Initial

community

Resultant

community

General concepts

http://www.logos-verlag.de/cgi-bin/buch/isbn/423 Just for fun

Things may become complicated

6

Things may become complicated

Propagules (young, seeds) are often easy,

nutritious and abundant food for other

organisms

Their survival should thus depend on: • Kinds of predators

• Number of predators

• Pattern of foraging

• Payoffs from foraging (number of propagules

predator can find)

Attalea butyracea

Distance from parent tree Number of seeds

Pre

dat

ion

rat

e

Theory

Distance from parent tree

See

dli

ng

s

However …

See

ds

7

Results

Distance from parent tree

See

dli

ngs

Distance from parent tree Number of seeds Pre

dat

ion

rate

See

ds

squirrels inverts agoutis

Invertebrates

Seed density

or health

Thus, a complex system emerges

Seedling density

Red-tailed

squirrel (attack

low densities)

-

+

-

-

Agouti (attack

high densities)

- +

What is a site anyway?

8

Who arrives in greatest numbers? - those that are close - those that are more numerous - those that more mobile

Differential performance

Likely candidates Small insects and arachnids (young spiders, mites) Also, small birds and mammals if site is not very isolated

3 months old lava flow

10 years

15 year old lava flow

20 year old lava flow

Effects of scale

What if the site is large (relative to dispersal distance?

Diagrammatically ..

Role of monkeys,

parrots

9

Effects of scale

What if the site is large (relative to

dispersal distance?

spatial waves; short distances from

the source site if:

a) dispersed by tree animals

(monkeys, birds, bats) that do not

enter open areas)

b) seeds belong to K-strategists

(heavy, adapted to germinate in

shady understory)

These are patterns produced by dispersal limitation

Effects of scale

What if the site is small (relative to dispersal distance?

Recolonization will

be synchronous

throughout the

site

Rich structure, multiple

levels

Same age; simpler

structure

Other consequences of new sites

Consider the case of forest regeneration after logging

10

Site availability

Initial coarse disturbance

Agents Landscape

Species availability

Size Severity Dispersion

Dispersal

Decay rate Land use

Propagule pool

After Pickett et al.

Dispersal

initiates

another

process

(succession)

Resource availability

Consumers

Climate Prior occupants

Germination Assimilation Growth rate

Eco- physiology

Identity Cycles Defenses Patchiness

Stress

Soils Microbes Neighbors

Competitors

Species

performance

Life history Allocation Reproductive timing Reproductive mode

Identity Consumers Fine-scale disturbance Resources

Allelopathy

Soil Microclimate

Inspection of right-hand lists alerts to the fact that all these phenomena, factors, or constraints depend on the area and time considered (scale-dependence)

Vegetation

dynamics