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The spatial dimension of population ecology. Case study I The local scale: necrophagous flies and their parasitoids. Arion ater. Basalys parva. Megaselia sp. Limosina ?sylvatica. Aspilota sp. Kleidotoma psiloides. The spatial distribution of individuals. Photo Polystyrol.

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slide1

The spatial dimension of population ecology

Case study I

The local scale: necrophagous flies and their parasitoids

Arion ater

Basalys parva

Megaseliasp

Limosina ?sylvatica

Aspilota sp

Kleidotoma psiloides

slide2

The spatial distribution of individuals

Photo Polystyrol

Each slug was covered by a beech leaf

Does spatial distribution change with abundance?

Do parasitoids and hosts differ in spatial distribution?

Is spatial distribution linked to resource availability?

Does spatial distribution contributes to population stability?

100 boxes arranged in a regular 10x10 m grid each with a dead slug

What is the spatial distribution of flies, parasitoids, and hyperparasitoids

slide4

The sequence of colonisation

The limiting factor of colonisation was carcass desiccation

Desiccation is dependent on plant cover

slide6

Coniceraschnittmanni

Megaselia sp1

Aspilota sp1

Orthostigma sp1

slide7

Aspilotasp1

Orthostigmasp1

Kleidotomapsiloides

Aspilotasp1

slide8

Spatial aggregation

Coefficient of variation

Morisita index

Mean crowding (Lloyd index)

N denote the occasions in each of the N sites.

Poisson random distribution

Poisson random: J = 1

Regular (segregated, overdispersed): J << 1

Clumped (aggregated, underdispersed): J >> 1

Statistical inference has to come from a Monte Carlo ranodmisation.

slide9

Lloyd index and species abundances

Parasitoids

Diptera

  • Necrophagous flies and their parasitoids :
  • Highly aggregated
  • Aggregation decreases with average abundance
  • Both guilds have the same degree of aggregation
slide10

Spatialsegregation of species?

Table of Pearson correlations (lower triangle) and the respectivesignificancelevels (upper triangle)

slide11

Biplots of principal component analyses

Limosina sp

PCA separates sphaerocerid species from C. schnittmanni and the other phorid species

C. schnittmanni

Aspilota sp1

PCA separates the abundant Aspilota sp1 and sp2

K. psiloides

Aspilota sp2

slide13

Case study II

The regional scale: fragmented landscapes and meta-populations

Meta-populations refer to the spread of local populations of a single species within a fragmented landscape. Local populations are connected by dispersal

Questions:

Minimum fragment size

Minimum dispersal rate for survival

Percentage of fragments colonised

Speed of genetic divergence within fragments

What is the influence of fragment edges?

How do corridors influence dispersal rates?

slide14

Case study II

The regional scale: fragmented landscapes and meta-populations

The Lotka – Volterra model of population growth

The spatial distribution of species is scattered among isolated fragments.

Fragments differ in population size

Levins (1969) assumed that the change in the occupancy of single spatially separated habitats (islands) follows the same model.

Assume P being the number of islands (total K) occupied. Q= K-P is then the proportion of not occupied islands. m is the immigration and e the local extinction probability.

Distance

Emigration/Extinction

Colonisations

The Levins model of meta-populations

The higher the population size is, the lower is the local extinction probability and the higher is the emigration rate

slide15

If we deal with the fraction p of fragments colonized

The canonical model of metapopulation ecology

Metapopulation modelling allows for an estimation of species survival in fragmented landscapes and provides estimates on species occurrences.

Colonisation probability is exponentially dependent on the average distance I of the islands and extinction probability scales proportionally to island size.

The standard equation of metapopulationmodeling

slide16

Extinction times

If we know local extinction times TL we can estimate the regional time TR to extinction

When is a metapopulation stable?

1200

1000

800

Median time to extinction

600

400

The meta-population is only stable if m > e.

200

0

0

1

2

3

4

5

6

7

0.5

If m and e are known p denotes the proportion of fragments colonised

p K

The condition for long-term survival

slide17

Bird metapopulations

Zosteropspoliogaster

Zosteropsabyssinicus

The lowland Z. abyssinicushas a continuous distribution.

The highland Z. poliogaster has a scattered mountain distribution.

It has a meta-population structure.

The highland species occurs in forest fragments

slide18

Morphological raw data

Bird call raw data

Allele frequency raw data

Data collected by J. C. Habel, TH Munich

slide19

ANOVA probabilities for no difference

Bird call patterns

Local birdcalls within Z. poliogaster are more different than between Z. poliogaster and Z. abyssinicus

Birdcall within the lowland Z. poliogasterdo not significantly differ

slide20

: Bird calls: Allele frequencies

: Morphology

Bird call patterns within Z. poliogaster differ more between local populations than do genetic and morphological charcters.

Northern and southern populations of Z. poliogaster differ considerable in bird dialect. Soon gen flow will cease despite of occasional migration.

slide21

Geographic distances in m

The average relative distance of a site to all other sites.

Species population occupancy modelling SPOM

a = 0.5b = 0.5c = 1

slide22

Species population occupancy modelling SPOM

High dispersal increases theprobability of occupancy.

High local mortality decreases local colonisation.

Distance between fragments has a high impact on colonisation probability.

The highly isolated Mt. Kulal has low occupancy probabilities.

For long-term stability of the meta-population at least 77% = 12 sites have to be occupied

3/√15 = 0.77

slide23

Is the species endangered?

The loss of habitats might provide to fast extinction

Zosteropspoliogaster is regionally not endangered despite of the higher local extinction probabilities