Ecosystems Population Responses to Environmental Stress

EcosystemsEcosystems

Population Responses to Population Responses to Environmental StressEnvironmental Stress


Response to Environmental StressResponse to Environmental Stress– Homeostasis - the maintenance of Homeostasis - the maintenance of

favorable internal conditions in a favorable internal conditions in a system despite flucutations in external system despite flucutations in external conditions conditions


Response to Environmental StressResponse to Environmental Stress– Feedback Loop - a circuit of sensing, Feedback Loop - a circuit of sensing,

evaluating, and reacting to changes in evaluating, and reacting to changes in environmental conditions as a result of environmental conditions as a result of information fed back into a systeminformation fed back into a system


Response to Environmental StressResponse to Environmental Stress– Feedback LoopFeedback Loop» Positive Feedback - a runaway cycle in Positive Feedback - a runaway cycle in

which a change in a certain direction which a change in a certain direction provides information that causes a system provides information that causes a system to change further in the same directionto change further in the same direction


Response to Environmental StressResponse to Environmental Stress– Feedback LoopFeedback Loop» Negative Feedback - a cycle in which a Negative Feedback - a cycle in which a

change in a certain direction leads to a change in a certain direction leads to a lessening of that changelessening of that change


Response to Environmental StressResponse to Environmental Stress– Ecosystem DisturbanceEcosystem Disturbance» Natural ChangesNatural Changes

Catastrophic ChangesCatastrophic Changes– DroughtDrought– FloodFlood– EarthquakeEarthquake– DiseaseDisease


Response to Environmental StressResponse to Environmental Stress– Ecosystem DisturbanceEcosystem Disturbance» Natural ChangesNatural Changes

Gradual ChangesGradual Changes– Climate changeClimate change– ImmigrationImmigration– EvolutionEvolution


Response to Environmental StressResponse to Environmental Stress– Ecosystem DisturbanceEcosystem Disturbance» Human-Caused ChangesHuman-Caused Changes

CatastrophicCatastrophic– DeforestationDeforestation– PlowingPlowing– PesticidesPesticides– FiresFires


Response to Environmental StressResponse to Environmental Stress– Ecosystem DisturbanceEcosystem Disturbance» Human-Caused ChangesHuman-Caused Changes

GradualGradual– SalinizationSalinization– Soil compactionSoil compaction– Depletion of groundwaterDepletion of groundwater– TourismTourism


Response to Environmental StressResponse to Environmental Stress– Ecosystem StabilityEcosystem Stability» Inertia Inertia » ConstancyConstancy» ResilienceResilience


Response to Environmental StressResponse to Environmental Stress– Ecosystem StabilityEcosystem Stability» Inertia - ability of a living system to resist Inertia - ability of a living system to resist

being disturbed or alteredbeing disturbed or altered» Constancy - ability of a living system to Constancy - ability of a living system to

maintain a certain sizemaintain a certain size» Resilience - ability of a living system to Resilience - ability of a living system to

rebound from an external disturbancerebound from an external disturbance


Response to Environmental StressResponse to Environmental Stress– Ecosystem StabilityEcosystem Stability» Do ecosystems have to have high Do ecosystems have to have high inertiainertia

and high and high resilienceresilience to be considered to be considered “stable”?“stable”?

Most ecosystems lack high inertia and resilienceMost ecosystems lack high inertia and resilience


Response to Environmental StressResponse to Environmental Stress– Signs of Ecosystem IllnessSigns of Ecosystem Illness» Drop in NPPDrop in NPP» Increased loss of nutrientsIncreased loss of nutrients» Decline in indicator speciesDecline in indicator species» Increased populations of pest speciesIncreased populations of pest species» Decline in species diversityDecline in species diversity» Presence of toxic chemicalsPresence of toxic chemicals


Response to Environmental StressResponse to Environmental Stress– Homeostasis and Time DelaysHomeostasis and Time Delays» Time delays between input of a stimulus Time delays between input of a stimulus

and the corresponding responseand the corresponding response Ozone depletionOzone depletion Global warmingGlobal warming COCO2 2 scrubbing scrubbing


Response to Environmental StressResponse to Environmental Stress– Homeostasis and SynergyHomeostasis and Synergy» Synergistic Reaction - a reaction that Synergistic Reaction - a reaction that

occurs when two or more processes occurs when two or more processes interact so that the combined effect is interact so that the combined effect is greater than the sum of their separate greater than the sum of their separate effects effects


Response to Environmental StressResponse to Environmental Stress– Homeostasis and SynergyHomeostasis and Synergy» Synergistic ReactionsSynergistic Reactions

Beneficial [COBeneficial [CO22 and photosynthesis] and photosynthesis] Harmful [ozone depletion + global warming]Harmful [ozone depletion + global warming]


Response to Environmental StressResponse to Environmental Stress– Species Diversity and Ecosystem Species Diversity and Ecosystem

StabilityStability» Ecosystems with higher species diversity Ecosystems with higher species diversity

have higher NPP and are more resilienthave higher NPP and are more resilient Biodiversity provides “insurance” against Biodiversity provides “insurance” against

catastrophecatastrophe



StabilityStability» Ecosystems with higher species diversity Ecosystems with higher species diversity

have higher NPP and are more resilienthave higher NPP and are more resilient Biodiversity provides “insurance” against Biodiversity provides “insurance” against

catastrophecatastrophe



StabilityStability» Tropical Rain ForestsTropical Rain Forests

High species diversityHigh species diversity High inertiaHigh inertia Low resilienceLow resilience

– Most nutrients stored in vegetationMost nutrients stored in vegetation



StabilityStability» GrasslandsGrasslands

Low species diversityLow species diversity Low inertiaLow inertia

– Burn very easilyBurn very easily High resilienceHigh resilience

– Most biomass is undergroundMost biomass is underground


Response to Environmental StressResponse to Environmental Stress– Population Responses to StressPopulation Responses to Stress» Population Dynamics - the major abiotic and Population Dynamics - the major abiotic and

biotic factors that tend to increase or biotic factors that tend to increase or decrease the population size and the age decrease the population size and the age and sex composition of a speciesand sex composition of a species


Response to Environmental StressResponse to Environmental Stress– Population Responses to StressPopulation Responses to Stress» Population DynamicsPopulation Dynamics

SizeSize Density - number of individuals per area)Density - number of individuals per area) Dispersion - spatial distribution of species in Dispersion - spatial distribution of species in

their habitattheir habitat



Biotic Potential - the maximum rate at which a Biotic Potential - the maximum rate at which a population could grow if it had unlimited population could grow if it had unlimited resourcesresources

Environmental Resistance - all factors that act to Environmental Resistance - all factors that act to limit the growth a populationlimit the growth a population



Carrying Capacity - the number of individuals of Carrying Capacity - the number of individuals of a given species that can be sustained indefinitely a given species that can be sustained indefinitely in a given area in a given area



Factors influencing carrying capacityFactors influencing carrying capacity– Interspecific and intraspecific competetionInterspecific and intraspecific competetion– ImmigrationImmigration– EmigrationEmigration– Catastrophic eventsCatastrophic events– Food and water supplyFood and water supply– HabitatHabitat


Response to Environmental StressResponse to Environmental Stress– Population Density and Population Population Density and Population

GrowthGrowth» Density-Dependent Population ControlsDensity-Dependent Population Controls

Increase in significance as population size Increase in significance as population size increasesincreases– Competition for resourcesCompetition for resources– PredationPredation– ParasitismParasitism



GrowthGrowth» Characteristics of dense populations:Characteristics of dense populations:

Low birth ratesLow birth rates Slow growth ratesSlow growth rates High death ratesHigh death rates



GrowthGrowth» Density-Independent Population ControlsDensity-Independent Population Controls

Affect a population’s size regardless of sizeAffect a population’s size regardless of size– Natural disastersNatural disasters– DeforestationDeforestation– Spraying of pesticidesSpraying of pesticides



GrowthGrowth» Reproductive Strategies for SurvivalReproductive Strategies for Survival

r-strategistsr-strategists K-strategistsK-strategists



GrowthGrowth» Survivorship CurvesSurvivorship Curves

Show number of survivors of each age group for Show number of survivors of each age group for a particular speciesa particular species– Late LossLate Loss– Constant LossConstant Loss– Early LossEarly Loss

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Ecosystems Population Responses to Environmental Stress