Ben-Gurion University of the Negev. Agroecology. Ecological understanding of farming systems 5. Biodiversity

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1 Ben-Gurion University of the Negev Agroecology Ecological understanding of farming systems 5. Biodiversity Diversity in general Biodiversity in nature Kinds of biodiversity Species diversity Landscape diversity BBoeken

2 Diversity Diversity is a multi-dimensional concept, not a single scalar. It describes an assemblage with >1 items, and relates to numbers of different kinds of items, their differences and configuration. 10 items 2 categories 10 items 2 categories 10 items 3 categories 6 items 3 categories 16 items 16 categories Differences: properties and abundances (numbers) of types (categories) Differences in properties among items within types are smaller than those between them. Differences in abundances reveal assemblage structure. 2

3 Biodiversity Genetic diversity Genotypes (within and among populations) Phenotypic trait groups Taxonomic diversity Species diversity Genera, families, etc. Functional diversity Functional groups (trophic levels, guilds, growth-forms, sizes) E.g., biomass producers, landscape modulators, N-fixers, litter producers, denitrifiers, granivores, folivores, predators, scavengers, parasites, etc.) Response diversity within functional groups Landscape diversity Patch types (at all scales) Successional stages Land use patterns 3

4 Species diversity Number of species (S) (species density in samples, species richness for a large area) depends on the number of individuals (N), due to Density of organisms. Area sampled (A) N=4 N=8 N=10 For any given N, S depends on: Diversity of habitats/sites (patches) with different species suitability Varying chances of arrival (species availability) Species interactions (competition, facilitation, predation). 4

5 Species richness Number of species depends on density and area: S = ƒ(n,a) Resampling from one sample of annual plants No. of Species (S) No. of Species (S) S/Log(N) Iterated S rarefaction Fisher's α No. of Individuals (N) Mauritius plants No. of Species Log Area (m 2 ) Fisher's α! Correction for density! Fisher s α! Rarefaction 5

6 Assemblage structure Species abundances Dominance structure Equitability Rank-abundance Due to differential performances and Interactions among species. Measures of equitability (evenness) Simpson s E = (1/Σ P i2 )/S Shannon s J = -Σ P i ln (P i )/ln (S) Pooling at different degrees of aggregation Relative abundance P i Samples, plots, etc Sticap Brofas AnaarvSilcol Avebar Rebpin Crust Shrub patches Dominance rank i Relative abundance P i Brofas Anaarv Sticap Silcol Rebpin Avebar Crust Shrub patches Dominance rank i Herbaceous plant communities in semi-arid shrubland, Park Shaked LTER, northern Negev, Israel 6

7 Species composition Identity and co-occurrence of species By ordination (PCA, RDA, DCA, CCA) Similarity among species Co-occurrence in samples Associations among species Coenoclines (compositional gradients) Abundance n i SD units Ordination Axis 1 Similarity among samples (patches) Species preferences for patch types Ecoclines (ecological gradients, zonation) Lakeshore, Sweden 7

8 Landscape diversity Landscape units: Patches At all scales (resolution and extent) Relevant for observation of process or phenomenon (e.g., biodiversity) 1 cm Biocrust, Park Shaked, Northern Negev Shrub and biocrust, Park Shaked, Northern Negev Patch types Number/frequency of patch types Discrete patches or gradients Size distributions Hillside, Mojave Desert, California 8

9 Patch types and patchiness Patch properties and patch types Topography/elevation Surface structure and cover Soil structure Resource availability and supply Presence of enemies Accessibility Patchy shrubland, Park Shaked, Northern Negev Spatial arrangement of patches Mosaics, patch-matrix situations Distance distributions of patch types Connectivity, leakiness Interfaces Transitions in time 9

10 Landscape relations Connections among patches for organisms Same patch type: Corridors, stepping stones; vectors Different patch types: Obstacles, edge effects Species specific: locomotion, dispersal Patches and resource flows Source-sink relations (redistribution of water, nutrients, OM) Larger-scale connectivity and resource loss Patches and species diversity Augmentation, dispersal Metapopulation dynamics Colonization, extinction, incidence Assemblage contrasts pinker.wjh.harvard.edu Spatial scales Species-specific Relations among scales Cause and effect at different scales 10

11 Patch formation Effects of ecosystem engineers Landscape modulators Biotic disturbance agents Desert tree (Pistacia atlantica), Central Negev Porcupine digging, Central Negev Disturbance regimes Abiotic agents (wind, water, fire, quakes, etc.) Forest fire 11