biol270chap_4_lec9

biol270chap_4_lec9 - Ecosystems Responses to Disturbance...

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Unformatted text preview: Ecosystems Responses to Disturbance Disturbance Ecological succession Disturbance and resilience Succession and Disturbance Succession Succession and Disturbance Succession Ecological succession: the orderly and progressive replacement of one community type by another until a climax stage is reached. – Primary­ no previous biotic community – Secondary­ previously occupied by a community Primary Succession Primary Secondary succession Secondary Primary succession Secondary succession Secondary succession Secondary Aquatic Succession Aquatic Ecological resilience magnitude of disturbance that can be absorbed before the system changes its structure Disturbance and Resilience Disturbance Ecological steady state: an ecological community or ecosystem that is resilient and in a state of dynamic equilibrium Disturbance and Resilience Disturbance Ecological steady state: an ecological community or ecosystem that is resilient and in a state of dynamic equilibrium Disturbance and Resilience Disturbance There are numerous potential ecological steady states (dynamic equilibrium) Disturbance and Resilience Disturbance A disturbance (perturbation) acts as a force and shifts the ecological community Disturbance and Resilience Disturbance Tipping point- less disturbance is needed to shift to alternate steady state (very unstable) Disturbance and Resilience Disturbance Non-equilibrium state- unstable ecosystem structure (unstable interactions) that result in rapid turnover in species composition and distributions Disturbance and Resilience Disturbance Alternate steady state- dynamic equilibrium Note the force needed to return to the original steady state (The role of management or let nature take its course) Disturbance and Resilience Disturbance Disturbance and Resilience Disturbance Disturbance and Resilience Disturbance Disturbance and Resilience Disturbance Disturbance and Resilience Disturbance Disturbance and Resilience Disturbance Disturbance and Resilience Disturbance Mechanisms of resilience Mechanisms Functional redundancy: (the rivets in the plane) The more species with similar “ecological role” (function) the more stable (resilient) a system will be. A disturbance (perturbation) can remove species but others are there to perform vital functions. Diversity Stability (importance of biodiversity) The landscape mosaic and patch dynamics (largely driven by disturbance) think colonizers Importance of scale Importance Landscape mosaic Patch dynamics (What is a disturbance?) Landscape mosaic What is a disturbance? (Temporal frequency) Is fire always a disturbance? Is fire always a disturbance? Fire in the southeast History of fire in the southeast History S tructure ope canopy, he :n rbace ous ground cove r History of fire in the southeast History Ple istoce ne y - 10,000 y BP) Pre olum -C bian Holoce (9,000 ne 500 y BP) (1.64x10 6 History of fire in the southeast History Post Europe contact (500 y BP – pre nt) an se Nicolas Sanson 1690 History of fire in the southeast History Post-e urope contact (500 y BP an – pre nt) se – Post­civil war northern influences History of fire in the southeast History Post-e urope contact (500 y BP an – pre nt) se Industrial forestry Fire Exclusion and the low-country Longleaf ecosystems > 97 % reduction 50 % in SC 1950 Structure Biological consequences of fire exclusion Biological Red cockaded Red cockaded woodpecker Flatwoods salamander Bobwhite quail Approximately 200 rare and endangered plants across the southeast Gopher tortoise Biodiversity – Biodiversity (biological diversity) refers to how many species, genera, phyla, life forms, guilds, genotypes, habitats, etc. exist within an area. Quantifying biodiversity Richness: the raw number of species, guilds, habitats etc. within a given area – (e.g., Species richness is the total number of species within a given area) Evenness: the numerical distribution of species, guilds, habitats etc. within a given area Low evenness High evenness + # ­ A B CDE F GH I Species A B CDE F GH I Species Three Scales of biodiversity Alpha diversity: is the biodiversity within a particular area, community or ecosystem, usually measured as richness. Beta diversity: variation in diversity among sites (alpha diversity) within a geographic region. Gamma diversity: the total biodiversity over a large area or region. It is the total of alpha and beta diversity. Biodiversity Alpha, Beta and Gamma Diversity Alpha, Beta and Gamma Diversity Biodiversity Alpha, Beta and Gamma Diversity Alpha, Beta and Gamma Diversity Biodiversity Alpha, Beta and Gamma Diversity Alpha, Beta and Gamma Diversity Congaree National Park Congaree National Park and International Biosphere Reserve 22,200 acres (8,984 ha) of old growth floodplain ecosystem Landscape management Pattern and Process Relationship not always clear Large spatial / temporal scales Floodplain landscape heterogeneity, flood pulse What drives crayfish biodiversity in a big What drives crayfish biodiversity in a big river floodplain: – Dispersal during flood pulse 1) Random distribution 2) Spatial autocorrelation – 3) Landscape patch dynamics Methods LIDAR (Light Detection and Ranging) elevation data MrSID (Multi­resolution Seamless Image Database) images Landscape Patches (habitats) (habitats) Oxbow lake (n=5) Gum pond (n=5) Slough (n=7) Landscape Patches (habitats) (habitats) Stream (n=7) Gut (n=7) Floodplain (n=7) Trapped (96 trap hours) Methods Electroshocked (0.5 hours) Dip netted (0.5 hours) Burrowing crayfish nets (336 trap hours) Analyses – 6 Species total – Only adult size crayfish – Species P/A at site Is beta diversity the result of dispersal during a flood pulse that results in random distribution? distribution? Ho: Species occurrence is random across the landscape. Fisher’s exact X2 = 71.16, df = 25, P < 0.0001 Is beta diversity the result of dispersal during a flood pulse that results in spatial autocorrelation? autocorrelation? Ho: No correlation between ecological distance and geographic distance 1) Ecological distance: Bray­Curtis (Sorensen) dissimilarity index 2) Geographic distance Mantel test on ecological and Mantel test on ecological and geographic distance matrices a a b c d e ­ .23 .17 .46 .39 b .23 ­ .54 .23 .92 c .17 .54 ­ .46 .81 d .46 .23 .46 ­ .52 e .39 .92 .81 .52 ­ a a b c d e ­ 322 b ­ c d e 26 322 415 503 136 192 448 ­ 567 439 ­ 334 ­ 415 136 503 192 567 26 448 439 334 Mantel Test Mantel Matrixes 31 X 31 r = 0.018 0.018 P = 0.82 1.2 1 0.8 0.6 0.4 0.2 0 Ecological distance 0 5000 10000 15000 20000 Geographic distance Beta diversity is a product of Beta landscape patch dynamics Beta diversity within landscape patches will be lower than among Beta diversity is a product of Beta landscape patch dynamics Design Matrix: Mantel test Design Matrix: Mantel test a a b c d e 0 .23 .17 .46 .39 b .23 ­ .54 .23 .92 c .17 .54 ­ .46 .81 d .46 .23 .46 ­ .52 e .39 .92 .81 .52 ­ a a b c d e ­ 0 0 1 1 b 0 ­ 0 1 1 c 0 0 ­ 0 0 d 1 1 0 ­ 0 e 1 1 0 0 ­ Beta diversity is a product of Beta llandscape patch dynamics andscape Ho: Patterns of beta diversity within and among patches are not different than expected by random 0.8 0.7 0.6 Design Matrix: Mantel test Design Matrix: Mantel test Ave. ecological distance 0.5 0.4 0.3 0.2 0.1 0 within among r = 0.22 P = 0.00001 Design matrix Conclusions A significant portion of crayfish beta diversity is the result landscape patch dynamics – Flood control that alter floodplain dynamics impact crayfish biodiversity – Importance of maintaining large scale processes for biodiversity conservation ...
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