Combined effects of global climate change and toxicants are complex and can be exacerbated or compensated for at higher levels of biological organization. The study discusses 4 ecological mechanisms using 3 case studies: 1) Demographic processes can compensate or propagate individual impacts to population levels. 2) Climate change can reduce resistance and recovery from toxicants at population and community levels. 3) Acquired tolerance to stressors often comes at a cost of reduced genetic diversity and increased susceptibility. 4) Species vulnerability is influenced by traits and landscape changes from climate change altering toxicant exposures. Long-term experiments incorporating realistic climate projections are needed to make reliable predictions.

1. Combined and interactive effects of global
climate change and toxicants on populations
and communities.
MOE, J., DE SCHAMPHELAERE, K., CLEMENTS, W., SORENSEN, M., VAN DEN
BRINK, P., LIES, M.; 2013; Environmental Toxicology and Chemistry, Vol 32, No. 1, pp.
49-61.
Group 5
Herzallah, Mohammed A.M.
Itoe, Nolinga Faith
Kimbi Yaah, Velma Beri
Lopez Karolys, Andrea Carolina
Mbah Bismarck, Nji Fowa
Mingo Ndiwago, Damian
Mumbanza Mundondo, Francis

2. Background
• Ecotoxicological Reserach
- Effect of chemical stressors, on population, communities and ecosystems.
• Changes in environmental conditions as a result GCC will affect the
vulnerability of populations and communities to toxicants.
- Stress due to GCC may reduce the potential for resistance to and recover from
toxicant exposure.
• The complexity of GCC and toxicants interactions.
• The release, fate, and exposure of toxicant are also likely to be affected by
GCC.
• Population and community level responses to toxicants under GCC are
likely to be influenced by various ecological mechanism.
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3. Goals, Questions
• How will GCC related changes in environmental conditions affect the
vulnerability of populations and comunities to toxicants ?
• How will combined impacts of toxicants and GCC-related stressors at the
individual level be influenced by ecological mechanisms at:
-
The population level: (growth rate)?
The community level: (species density, ecosystem, functions and services)?
• Focus on ecological mechanisms  four topics.
-
Demographic and interspecific processes influencing propagation of individuallevel responses.
Resistance, resilience, and recovery from disturbances.
Acquired tolerance to stressors and associated costs.
Species traits and population vulnerability in a landscape context.
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4. Approach
• Ecological mechanisms at the population and community levels
susceptible to:
- Compensate or exacerbate the individual-effects of stressors at the
higher level of biological organization.
• Design of a specific scheme to explain possible combined effects of
GCC and toxicant at the population and community levels (Fig 1)
• 4 topics (3 study cases) discussed to illustrate possible joint effect of
GCC and toxicant at population and community levels.
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5. Fig. 1 Combined impacts of GCC and chemical stressors across biological levels of
organization.
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6. Topics discussion and case
studies

7. Topics discussion and case studies
1.
Demographic and interspecific processes influencing propagation
of individual-level responses
At population level :
-
Density-dependent mechanisms compensating for the impact of stressors
(population-level impacts).
Sublethal and latent effects and the timing of multiple stressors in relation to
the life-history stages (stronger effects at population level).
Examples: Salamander vs Atrazine ; T and Hg vs nestling production in tree
swallows.
At community level :
-
Impact on species interaction and food web structures.
Examples: Polar bears- sea ice breakup-open water seal speciescontamination (Chlorinates, brominates); Tawny owls-colder winter-more
PCB- alternative prey (passerine birds).

8. Case Study 1
2. Resistance, resilience, and
recovery from disturbances.
Case study: impacts of global warming
and cyanotoxins on plankton communities
in lakes.
At population level:
- Chemical and region specific effects
of GCC on persistence of compound.
- Direct (T ) and indirect
(eutrophication) on population
recovery .
Ex. GCC contributes to prolong
recovery period (Fig 2)
At community level:
- Lower resistance to
contaminant, lower recovery as a
result of impairment by GCC.
Fig. 2 Impacts of global warming and cyanotoxins on
plankton communities in lakes.

9. Population level
- When a population is exposed to a stressor over
multiple generations, natural selection may favor
genotypes that are more tolerant to this stressor 
increase the mean tolerance of the population.
- Local adaptation of field populations with a history of
stress exposure, for both chemical contaminants and
climate-related factors.
Genetic adaptation to a toxicant usually results in a
reduction of genetic diversity at the population level.
Fig 3. Simplified visualization of the cost
of tolerance concept.
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10. Case study 2
3. Acquired resistance to stressors
and associated costs.
Case study: Impacts of ultraviolet
radiation and metals on invertebrate
communities in streams.
At population level
-
Genetic acquired resistance (reduced
fitness).
Example: Oligochaete vs Cd
-
Reduction of genetic diversity
Increased susceptibility to different
environmental stressors
Example: Fresh water snails-Cd-T
At community level
-
Pollution-induced community
tolerance: elimination of most sensitive
species, less species with tolerance to
GCC-related stressors. (Fig.4).
Fig. 4 Impacts of ultraviolet (UV) radiation and metals on
invertebrate communities in streams

11. Community Level
Fig 5. Conceptual model of impacts of global
climate change (GCC) on species composition
and toxicant sensitivity for a hypothetical
community in a given location.

12. Case study 3
4. Species traits and population
vulnerability in a landscape context
Case study 3: Impacts of future
climate-related pesticide use on
invertebrate communities in streams.
At population level
- Intrinsic sensitivity of species to
toxicant influenced by climatic
variables (T )
At community level
- Changes in community due to
toxicant exposure associated with
toxicological sensitivity, duration of
life cycle, migration (Fig 6).
- Alteration of community
vulnerability to toxicant with GCC
(shifts in spatial and temporal
species distribution).
Fig 6. Impacts of future climate-related pesticide use
on invertebrate communities in streams.

13. Conclusion
• The four topics discussed are relevant for:
- Interpreting existing observational data sets (case study 1).
- Generating testable hypotheses regarding future effects of GCC and
toxicant exposure (Case study 2 and 3).
- More case studies and testing are needed before validating these
ecological principles as a tool to make predictions about different
climate and toxicant combinations of effects in different ecosystems
• Long-term ecotoxicological experiments that incorporate a realistic
downscaling of future climate projections in combination with high
environmental variation would enable more reliable predictions of
toxicant impacts under climate change.
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14. Critical Evaluation
•
The four ecological mechanisms used in the study are appropriate .
Reason : They show the relationship at various levels of biological organization.
• The approach of using case studies is appropriate .
Reason : The compounded effects of GCC and toxicants often lead to surprises
at the population level. Hence case studies are necessary to have specific results
• The results cannot be used for ERA .
• More case studies are needed for predictions to be possible
• Various communities can be exposed to known concentrations and altering
climatic parameter thereby simulating GCC in lakes (Experimental Lake Area in
Canada) . This will be an experiment in a natural system
•
Specific schemes should be developed for different ecosystems starting by the
most vulnerable
•
The effects of climate change on humans and how they are trying to adapt to the
latter have not been considered in the framework developed ( quantity and
diversity of new chemicals)
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