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

The spatial distribution of individuals 100 boxes arranged in a regular 10x10 m grid each with a dead slug What is the spatial distribution of flies, parasitoids, and hyperparasitoids 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? Photo Polystyrol Each slug was covered by a beech leaf

The complete food web of dead Arion snails

The sequence of colonisation The limiting factor of colonisation was carcass desiccation Desiccation is dependent on plant cover

Slug weight (g) Conicera schnittmani Megaselia ruficornis Megaselia pulicaria Gymnophora arcuata Limosina spPsychoda sp Fannia immutica Panorpa sp N weight (mg) N N N N N N N Coordi- nates Slug weight (g) Aspilota sp1Aspilota sp2 Orthostigma sp1 Aspilota sp4Aspilota sp5 Kleidotoma psiloides N parasitism rate N N N N N The raw data

Conicera schnittmanniMegaselia sp1 Aspilota sp1Orthostigma sp1

Aspilota sp1Orthostigma sp1 Aspilota sp1 Kleidotoma psiloides

Spatial aggregation Coefficient of variationMorisita index Mean crowding (Lloyd index) Poisson random distribution Poisson random: J = 1 Regular (segregated, overdispersed): J << 1 Clumped (aggregated, underdispersed): J >> 1 N denote the occasions in each of the N sites. Statistical inference has to come from a Monte Carlo ranodmisation.

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

Conicera schnittmani Megaselia ruficornis Megaselia pulicaria Gymnophora arcuata Limosina spPsychoda sp Fannia immutica Panorpa sp Conicera schnittmani Megaselia ruficornis Megaselia pulicaria Gymnophor a arcuata Limosina sp Psychoda sp Fannia immutica Panorpa sp Aspilota sp1Aspilota sp2Orthostigma sp1Aspilota sp4Aspilota sp5 Kleidotoma psiloides Aspilota sp Aspilota sp Orthostigma sp Aspilota sp Aspilota sp Kleidotoma psiloides Spatial segregation of species? Table of Pearson correlations (lower triangle) and the respective significance levels (upper triangle)

Aspilota sp1 Aspilota sp2 K. psiloides C. schnittmanni Limosina spBiplots of principal component analyses PCA separates sphaerocerid species from C. schnittmanni and the other phorid species PCA separates the abundant Aspilota sp1 and sp2

Necrophagous DipteraParasitic Hymenoptera Large number of species Higher diversityLower diversity Colonization susceptible to desiccation of the carcassParasitism fairly independent of carcass desiccation Densities of early colonizers do not depend on the weight of the carrion Parasitism rates independent of the weight of the carrion Densities of late colonizers correlate positively with the weight of the carrion Parasitism in dominant species is not density dependent Low interspecific competition Pronounced interspecific competition only at high parasitism rates High competition between the necrophagous flies and large predators and necrophages - High impact of large predators and necrophages on the mortality rates Parasitism rates not influenced by the presence of larger competitors of the hosts High degree of aggregation in the populations Negative correlation between abundance and degree of aggregation No marked correlation between parasitism and degree of aggregation Aggregation of late colonizing species negatively correlated with the weight of the carrion Aggregation independent of the number of hosts Differences in the populations of necrophages and their parasitoids

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?

The spatial distribution of species is scattered among isolated fragments. Fragments differ in population size The higher the population size is, the lower is the local extinction probability and the higher is the emigration rate Distance Case study II The regional scale: fragmented landscapes and meta-populations The Lotka – Volterra model of population growth 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. Colonisations Emigration/Extinction The Levins model of meta-populations

Colonisation probability is exponentially dependent on the average distance I of the islands and extinction probability scales proportionally to island size. The canonical model of metapopulation ecology Metapopulation modelling allows for an estimation of species survival in fragmented landscapes and provides estimates on species occurrences. If we deal with the fraction p of fragments colonized The standard equation of metapopulation modeling

Extinction times When is a metapopulation stable? The meta-population is only stable if m > e. If we know local extinction times T L we can estimate the regional time T R to extinction p K 0.5 Median time to extinction The condition for long-term survival If m and e are known p denotes the proportion of fragments colonised

Bird metapopulations Zosterops abyssinicus Zosterops poliogaster The lowland Z. abyssinicus has 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

SpeciesRegionNWingTarsusWeightGPS Z. poligasterCH-Satellite °35´S; 37°51´E Z. poligasterCH-Simba valley °42´S; 37°55´E Z. poligasterMount Kasigau °49´S; 38°39´E Z. poligasterMt. Kulal °39´N; 36°56´E SpeciesRegionSite Starting frequency Lowest frequency Highest frequency Frequency range Length of call Z.abyssinicusChyulu LowandsHunters Lodge Z.abyssinicusChyulu LowandsHunters Lodge Z.abyssinicusChyulu LowandsHunters Lodge Z.abyssinicusChyulu LowandsHunters Lodge Z.abyssinicusChyulu LowandsHunters Lodge Locatio n Locus Fragme nt length Mt. Kasiga u TH Chawia TH Mbolol o TH Nganga o Chyulu Hills Aberda res Mt. Kulal Chulu lowlands Cu_ Cu_ Cu_ Zl Zl Zl Zl Zl Zl Morphological raw data Bird call raw data Allele frequency raw data Data collected by J. C. Habel, TH Munich

Bird call patterns Species P. abyssinicusP. poliogaster Region Chyulu lowlandsTaita lowlandsChyulu hillsTaita hills Aberdare s Site Hunters Lodge Kibwesi Mtito Andei MumoniDembwaMwatateSatelliteSimba Mt. Kasigau MbololoNgangao Aberdare s P. abyssinicus Chyulu lowlands Kibwesi0.33 Mtito Andei < Mumoni Taita lowland s Dembwa Mwatate P. poliogaster Chyulu hills Satellite0.49<0.001 Simba <0.001 Taita hills Mt. Kasigau < Mbololo< < Ngangao < <0.001 Aberdar es <0.001 Mt. Kulal 0.05< < Local birdcalls within Z. poliogaster are more different than between Z. poliogaster and Z. abyssinicus Birdcall within the lowland Z. poliogaster do not significantly differ ANOVA probabilities for no difference

: Bird calls : Allele frequencies : Morphology Northern and southern populations of Z. poliogaster differ considerable in bird dialect. Soon gen flow will cease despite of occasional migration. Bird call patterns within Z. poliogaster differ more between local populations than do genetic and morphological charcters.

DistCH-SatelliteCH-Simba_valleyMt_KasigauMt._KulalChawia CH-Satellite CH-Simba_valley Mt_Kasigau Mt._Kulal Chawia Geographic distances in m Sum Rel sum The average relative distance of a site to all other sites. Species population occupancy modelling SPOM Site IA [ha]p0p1p2p3p4p5p6 CH-Satellite CH- Simba_valley Mt_Kasigau Mt._Kulal Chawia Fururu =AE56+$W$53*EXP(-$Y$53*$W56)*AE56*(1-AE56)-$X$53*1/$X56*AE56 a = 0.5 b = 0.5 c = 1

a b c1115 Sitep6 CH-Satellite CH-Simba_valley Mt_Kasigau Mt._Kulal Chawia Fururu MachaE Mbololo Mwachora Ndiwenyi Ngangao Ronge Vuria Wundanyi YaleS Species population occupancy modelling SPOM High dispersal increases the probability 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. 3/√15 = 0.77 For long-term stability of the meta-population at least 77% = 12 sites have to be occupied

Is the species endangered? Site p61-p6 Extinction time CH-Satellite CH- Simba_valley Mt_Kasigau Mt._Kulal Chawia Fururu MachaE Mbololo Mwachora Ndiwenyi Ngangao Ronge Vuria Wundanyi YaleS TLTL P11 TRTR Zosterops poliogaster is regionally not endangered despite of the higher local extinction probabilities Extinction time The loss of habitats might provide to fast extinction