Effects to Communities & Ecosystems

Transcription

1 Biology 5868 Ecotoxicology Effects to Communities & Ecosystems April 18, 2007

2 Definitions Ecological Community an assemblage of populations living in a prescribed area or physical habitat [It is] the living part of the ecosystem. (Odum, 1971) (biotic community) a naturally occurring assemblage of plants and animals that live in the same environment, are mutually sustaining and interdependent, and are constantly fixing, utilizing and dispensing energy. Smith, 1975 Ecosystem a concept that combines the biota (community) and the abiotic environment into an organized system.the eco part of the word implies environment; the system part, a complex of coordinated units. Smith, 1975 NOTE Community and Ecosystem are abstractions, and should not be confused with reality! application is dependent on scale (time and space), distinctiveness of system boundaries, and on the particular qualities under study

3 Perspectives on Community Effects Traditional hierarchical approach in which effects on a subordinate level lead to effects at the next higher level of organization: effects on individuals effects on populations effects on populations effects on communities Emerging effects on a given level can lead to effects at far removed levels of organization: effects on keystone species effects on multiple keystone dependent species (i.e. communities) effects on sensitive species effects on tolerant species (i.e. communities) Emergent properties complex properties arising out of simple systems/interactions emergent properties generally cannot be predicted based solely on an understanding of the components of the system

4 Vulnerable Communities/Ecosystems Vulnerability: The susceptibility to irreversible damage from toxicants. Vulnerable communities lack: Elasticity the ability of a community to return to a pre stressed condition. Inertia the ability of a community to resist change; influenced by structural redundancy Resilience the number of times a community can return to its normal state after perturbation (influenced by Elasticity).

5 Assessing Effects on Communities Assessment scales: Individual species/populations keystone species sensitive species Two or a few species paired relationships Multiple taxa indicies

6 Assessing Effects on Communities Bioindicators Community: structure diversity competitive interactions energy transfer efficiency rates of change in community structure successional states chemical parameters and nutrient flow Ecosystem: mean patch size energy flow persistence

7 Assessing Effects on Communities Most Sensitive Species Approach Uses the results from the most sensitive of all species tested as an indicator of the concentration (or dose) most likely to be protective of all species in the community. Advantage Relatively simple and cost effective. Disadvantage The array of species tested rarely encompasses the array of species in the (natural) community. What if the most sensitive species tested was not the most sensitive species in the community? Modified Most Sensitive Species Approach Pool NOECs from various species and then statistically estimate a community level NOEC that will afford protection to a certain percentage of all species in the community (Figure 11.1). Advantage The protective concentration is derived from a comprehensive evaluation of a multi species data base. Disadvantage The estimated (safe) concentration rarely protects 100 % of the species in the community. What if the unprotected percentage included a keystone species? Also, remember that if individual or pooled NOECs are established at the 0.95% level, 5% of species could still be lost; is this an acceptable loss to the community?

8 Interspecies competition: Bioindicators Competition Interference Competition Toxicant s sublethal effects lead to one competing species benefiting or suffering relative to its competitors. Classic example is the effect of Cadmium on Bluegill behavior and, ultimately,territoriality. Exploitation Competition Toxicant s sublethal effects impact one species ability to compete for a limited resource relative to its competitors.. Zooplankton community exhibited species specific differences in algal filtration rate in the presence of a toxicant

9 Bioindicators Predation Predation scenarios: 1. No direct lethal or sublethal effects on predator + lethal effect on prey = indirect sublethal effect on predator population Contaminant forced Predator to reallocate energy in response to diminished Prey. 2. No lethal or sublethal effects on predator + sublethal effect on prey = predator causes extinction of prey population Prey s defenses or predator avoidance behavior was influenced by contaminant. Predators must allocate energy to optimize fitness; e.g. establishing optimal foraging strategies contaminants can cause functional responses that adjust optimal foraging e.g. for predators; searching, identification, choice, pursuit, capture, handling, ingestion

10 Indicies of Community Structure Structural Qualities: species richness evenness diversity (heterogeneity) Species Richness The number of species present in the community. Because the number of species present increases with sampling effort, and because it is impossible to sample all individuals, species richness is expressed relative to a standardized sample size; e.g. Rarefaction Estimate of Richness (RER). e.g. ten species of coleoptera are expected to be found in a standard sample of 200 insects.

11 Community Structure Species Evenness The extent to which individuals in the community are uniformly distributed among species % 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% Community 1 Community 2 Species C Species B Species A

12 Community Structure Species Diversity the extent of heterogeneity among species comprising a community. reflects the magnitudes of both species richness and evenness. Diversity Quantification Shannon Diversity Index (Equation 11.1 in text) Brillouin Diversity Index (Equation 11.2 in text) Brillouin Index estimates diversity for the sample; Shannon Index estimates diversity for the community. therefore, Brillouin estimates < Shannon estimates

13 Community Structure Diversity Community 1 Community 2 Community 3 Community 4 Sp. A Sp. B Sp. C Sp. D

14 Community Indices and Contaminant Effects Caution! Community Indices (e.g. species richness, evenness, diversity, etc.) are not measures of toxicant induced stress, but simply describe communities. However, they are often used to describe healthy v. unhealthy systems. Justified? values for species indices often decline as a consequence of toxicant exposure however, the relationship between statistical and biological significance is unclear (same old problem) also, effects of Functional Redundancy within communities and ecosystems limits utility of indicies overlapping/redundant functionalities within a community may mask structural changes; e.g. a species may be adversely impacted but the community remains functional. a community may be adversely impacted but the ecosystem remains functional.

15 Functional Redundancy Models Redundancy hypothesis terrestrial snails insects earthworms (keystone species) Function = Soil Bioturbation Community = Terrestrial Invertebrates

16 Rivet Popper hypothesis Functional Redundancy Models Road Kill Vertebrate Scavenger 1 Vertebrate Scavenger 2 Invertebrate Scavenger 1 Invertebrate Scavenger 2 Microbial Scavenger 1 Microbial Scavenger 2 Function = Decomposition Community = Various taxa are involved

17 Species Abundance Curves 120 relative abundance (log) number of species number of individuals abundance rank incorporate both species richness (x axis) and evenness (slope) most useful in a comparative mode for ecotox; ie compare communities before and after toxicant exposure compare exposed and non exposed (control) communities

18 Interpreting Species Abundance Curves number of species in the rank before toxicant after toxicant Changes in the shapes of species abundance curves after toxicant exposure can reflect a return to an earlier successional state; e.g. community dominance by an opportunistic species. 0 to 1 1 to 2 2 to 4 4 to 8 8 to to to to 128 rank (individuals/species) 128 to to 512 opportunistic species tend be r strategists, which tend to produce many offspring that grow rapidly to reproductive maturity. Colonizers in the absence of contaminants, a community will possess k strategists, which tend to produce fewer offspring that slowly mature to be strong competitors. Persisters Maturity index based on proportions of r strategists v. k strategists

19 Index of Biological Integrity (IBI) IBI s comprehensive community assessment tools first developed for use with aquatic ecosystems. species richness composition trophic characterization abundance condition numerical scores established for each criterion; summed to produce overall numerical score IBIs compared to expected IBI in the area for an undisturbed system The original IBI had 12 qualities of fish assemblages applicable to warm water, low gradient streams.

20 Metrics IBI for Fish Communities Rating of Metric Species richness and composition 1. Total number of fish species/native fish species 2. Number and identity of darter species (benthic) 3. Number and identity of sunfish species (water column species) expectations for metrics 1 5 vary with stream size and region 4. Number and identity of sucker species (long lived species) 5. Number and identity of intolerant species 6. Percentage of individuals as green sunfish (tolerant species) < > 20 Trophic composition 7. Percentage of individuals as omnivores < > Percentage of individuals as insectivorous cyprinids (insectivores) > < Percentage of individuals as piscivores (top carnivores) < < 1 Fish abundance and condition 10. Number of individuals in sample 11. Percentage of individuals as hybrids (exotics of simple lithophils) expectations vary with stream size and other factors 0 > 0 1 > Percentage of individuals with disease, tumors, fin damage, and skeletal anomalies 0 2 > 2 5 > 5 Karr, 1991

21 Total IBI Score (Sum of Metrics) Integrity Class of Site IBI Scores Attributes Excellent Comparable to the best situations without human disturbance; all regionally expected species for the habitat and stream size, including the most intolerant forms, are present with a full array of age (size classes); balanced trophic structure Good Species richness somewhat below expectation, especially due to the loss of the most intolerant forms; some species are present with less than optimal abundances or size distributions; trophic structure shows some signs of stress Fair Signs of additional deterioration include loss of intolerant forms, fewer species, highly skewed trophic structure (e.g. increasing frequency of omnivores and green sunfish or other tolerant species); older age classes of top predators may be rare Poor Dominated by omnivores, tolerant forms, and habitat generalists; few top carnivores; growth rates and condition factors commonly depressed; hybrids and diseased fish often present Very poor Few fish present, mostly introduced or tolerant forms; hybrids common; disease, parasites, fin damage, and other anomalies regular No fish Repeated sampling finds no fish Karr, 1991

22 Interpreting IBIs Advantages: distills information down to one number transferability of IBI like measures to other assemblages, including terrestrial Caveats: subject to the dominant paradigm of the time of formulation what is counted? what is left out? how are different taxa weighted? one number = loss of a lot of information e.g. very different systems can have equivalent index scores

23 Approaches to Assessing Communities Lower Fidelity to Nature Lower Uncertainty & Complexity $ Microcosms $$ Mesocosms $$$ Matched Ponds $$$$ Terrestrial Studies Higher Fidelity to Nature Higher Uncertainty & Complexity