Table 1.1. Ecological Surprises Caused by Complex Interactions

Voluntary or involuntary introductions or deletions of species often trigger unexpected alterations in the normal provision of ecosystem services by terrestrial, freshwater, and marine ecosystems. In all cases, the community and ecosystem alterations have been the consequence of indirect interactions among three or more species (C11, Table 11.2).

Study Case	Nature of the Interaction Involved	Ecosystem Service Consequences
Introductions
Top predators
Introduction of brown trout (Salmo trutta) in New Zealand for angling	trophic cascade, predator increased primary producers by decreasing herbivores	negative— increased eutrophication
Introduction of bass (Cichla ocellaris) in Gatun Lake, Panama	trophic cascade, top predator decreased control by predators of mosquito larvae	negative— decreased control of malaria vector
IIntroduction of pine marten (Martes martes) in the Balearic Islands, Spain	predator of frugivorous lizards (main seed dipersers)	negative— decreased diversity of frugivorous lizards due to extinction of native lizards on some islands; changes in dominant shrub (Cneorum tricoccon) distribution because marten replaced the frugivorous-dispersing role
Intraguild predators
Egg parasitoid (Anastatus kashmirensis) to control gypsy moth (Lymantria dispar)	hyperparasitism (parasitoids that use parasitoids as hosts)	negative— disruption of biological control of pests; introduced parasitoid poses risk of hyperparasitism to other pest-regulating native parasitoids
Gambusia and Lepomis fish in rice fields to combat mosquitoes	intraguild predator (adult fish feed on juveniles as well as on mosquito larvae)	opposed to goal— decreased control of disease vector (mosquito)
Intraguild preys
Opossum shrimp (Mysis relicta) in Canadian lakes to increase fish production	intraguild prey depletes shared zooplankton prey	opposed to goal— decreased salmonid fish production
Apparent competitors
Rats (Rattus spp) and cats (Felis catus) in Steward Island, New Zealand	rats induced high cat densities and increased predation on endangered flightless parrot (Strigops habroptilus)	negative— reduced diversity
Herbivores
Zebra mussel (Dreissena polymorpha) in Great Lakes, United States	zebra mussel reduced phytoplankton and outcompeted native bivalves	negative— reduced diversity positive— increased water quality
Mutualists
Myna bird (Acridotheres tristis) for worm pest control in Hawaiian sugarcane plantations	myna engaged in the dispersal of the exotic woody weed Lantana camara	negative— increased invasion by Lantana produced impenetrable thorny thickets; reduced agricultural crops and pasture carrying capacity and sometimes increased fire risk; displaced habitat of native birds
Ecosystem engineers
Earthworm (Pontoscolex corethrurus)in Amazonian tropical forests converted to pasture	dramatically reduces soil macroporosity and gas exchange capacity	negative— reduces soil macrofaunal diversity and increases soil methane emissions
C4 perennial grasses Schizachyrium condesatum, Melinis minutiflora in Hawaii for pasture improvement	increased fuel loads, fuel distribution, and flammability	negative— increases fire frequency, affecting fire-sensitive plants; reduced plant diversity; positive feedback for further invasion of flammable exotic species on burned areas
Nitrogen-fixing firetree (Myrica faya) in Hawaii	increases soil nitrogen levels in newly formed nitrogen-poor volcanic soils	negative— increased fertility, increased invasion by other exotics, reduced regeneration of native Metrosideros tree, alteration of successional patterns
Deletions/Harvesting
Top predators
Selective harvesting of piscivorous fishes in Canadian lakes	piscivorus fishes promote Daphnia that effectively suppresses primary (algal) production	negative— shifts from net carbon sinks in piscivorous-dominated to equilibrium or net carbon sources in planktivorous-dominated lake
Sea otter (Enhydra lutris) harvesting near extinction in southern California	cascading effects produced reductions of kelp forests and the kelp-dependent community	negative— loss of biodiversity of kelp habitat users
Pollution-induced reductions in predators of nematodes in forest soils	heavy metal bioaccumulation produced reductions nematophagous predators and increased herbivorous nematodes	negative— disruption of forest soil food webs; increases in belowground herbivory; decrease in forest productivity
Intraguild predators
Declining populations of coyote (Canis latrans) in southern California	releases in raccoons (Procyon lotor) and feral house cats	negative— threat to native bird populations
Overhavesting of seals and sea lions in Alaska	diet shifts of killer whales increased predation on sea otters	negative— conflict with other restoration programs; failure of reintroduction of sea otters to restore kelp forest ecosystems
Keystone predators
Harvesting of triggerfish (Balistaphus) in Kenyan coral reefs	triggerfish declines release sea urchins, which outcompete herbivorous fish	negative— increased bioerosion of coral substrates; reduced calcium carbonate deposition
Herbivores
Voluntary removal of sheep and cattle in Santa Cruz Island, United States, for restoration	release of the exotic plant component from top-down control	opposite to goal— explosive increases in exotic herbs and forbs and little recovery of native plant species
Overhavesting of seals and sea lions in Alaska	lack of fish grazers allowed macroalgae to outcompete coral following disturbances	negative— coral cover was reduced from 52% to 3%, and macroalgae increased from 4% to 92%
Ecosystem engineers
Voluntary removal of exotic tamarisk (Tamariscus sp.) for restoration of riparian habitats in Mediterranean deserts	long-established tamarisk has replaced riparian vegetation and serves as habitat to endangered birds	opposite to goal— reduction in biodiversity; structural changes in riparian habitats

Source: Millennium Ecosystem Assessment
 Ecosystems and Human Well-being: Biodiversity Synthesis (2005), p.26-27

Biodiversity & Human Well-being

Direct cross-links to the Global Assessment Reports of the Millennium Assessment

Box 1. Biodiversity and Its Loss— Avoiding Conceptual Pitfalls

Box 1.1. Linkages among Biodiversity, Ecosystem Services, and Human Well-being

Box 1.2. Measuring and Estimating Biodiversity: More than Species Richness

Box 1.3. Ecological Indicators and Biodiversity

Box 1.4. Criteria for Effective Ecological Indicators

Box 2. MA Scenarios

Box 2.1. Social Consequences of Biodiversity Degradation (SG-SAfMA)

Box 2.2. Economic Costs and Benefits of Ecosystem Conversion

Box 2.3. Concepts and Measures of Poverty

Box 2.4. Conflicts Between the Mining Sector and Local Communities in Chile

Box 3.1. Direct Drivers: Example from Southern African Sub-global Assessment

Box 4.1. An Outline of the Four MA Scenarios

Box 5.1. Key Factors of Successful Responses to Biodiversity Loss

Figure 3.3. Species Extinction Rates

Figure 1.1. Estimates of Proportions and Numbers of Named Species in Groups of Eukaryote Species and Estimates of Proportions of the Total Number of Species in Groups of Eukaryotes

Figure 1.2. Comparisons for the 14 Terrestrial Biomes of the World in Terms of Species Richness, Family Richness, and Endemic Species

Figure 1.3. The 8 Biogeographical Realms and 14 Biomes Used in the MA

Figure 1.4. Biodiversity, Ecosystem Functioning, and Ecosystem Services

Figure 2. How Much Biodiversity Will Remain a Century from Now under Different Value Frameworks?

Figure 2.1. Efficiency Frontier Analysis of Species Persistence and Economic Returns

Figure 3. Main Direct Drivers

Figure 3.1. Percentage Change 1950–90 in Land Area of Biogeographic Realms Remaining in Natural Condition or under Cultivation and Pasture

Figure 3.2. Relationship between Native Habitat Loss by 1950 and Additional Losses between 1950 and 1990

Figure 3.3. Species Extinction Rates

Figure 3.4. Red List Indices for Birds, 1988–2004, in Different Biogeographic Realms

Figure 3.5. Density Distribution Map of Globally Threatened Bird Species Mapped at a Resolution of Quarter-degree Grid Cell

Figure 3.6. Threatened Vertebrates in the 14 Biomes, Ranked by the Amount of Their Habitat Converted by 1950

Figure 3.7. The Living Planet Index, 1970–2000

Figure 3.8. Illustration of Feedbacks and Interaction between Drivers in Portugal Sub-global Assessment

Figure 3.9. Summary of Interactions among Drivers Associated with the Overexploitation of Natural Resources

Figure 3.10. Main Direct Drivers

Figure 3.11. Effect of Increasing Land Use Intensity on the Fraction of Inferred Population 300 Years Ago of Different Taxa that Remain

Figure 3.12. Extent of Cultivated Systems, 2000

Figure 3.13. Decline in Trophic Level of Fisheries Catch since 1950

Figure 3.14. Estimated Global Marine Fish Catch, 1950–2001

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.15. Estimates of Forest Fragmentation due to Anthropogenic Causes

Figure 3.16. Fragmentation and Flow in Major Rivers

Figure 3.17 Trends in Global Use of Nitrogen Fertilizer, 1961–2001 (million tons)

Figure 3.18 Trends in Global Use of Phosphate Fertilizer, 1961–2001 (million tons)

Figure 3.19. Estimated Total Reactive Nitrogen Deposition from the Atmosphere (Wet and Dry) in 1860, Early 1990s, and Projected for 2050

Figure 3.20. Historical and Projected Variations in Earth’s Surface Temperature

Figure 4. Trade-offs between Biodiversity and Human Well-being under the Four MA Scenarios

Figure 4.1. Losses of Habitat as a Result of Land Use Change between 1970 and 2050 and Reduction in the Equilibrium Number of Vascular Plant Species under the MA Scenarios

Figure 4.2. Relative Loss of Biodiversity of Vascular Plants between 1970 and 2050 as a Result of Land Use Change for Different Biomes and Realms in the Order from Strength Scenario

Figure 4.3. Land-cover Map for the Year 2000

Figure 4.4. Conversion of Terrestrial Biomes

Figure 4.5. Forest and Cropland/Pasture in Industrial and Developing Regions under the MA Scenarios

Figure 4.6. Changes in Annual Water Availability in Global Orchestration Scenario by 2100

Figure 4.7. Changes in Human Well-being and Socioecological Indicators by 2050 under the MA Scenarios

Figure 6.1. How Much Biodiversity Will Remain a Century from Now under Different Value Frameworks?

Figure 6.2. Trade-offs between Biodiversity and Human Well-being under the Four MA Scenarios

Table 1.1. Ecological Surprises Caused by Complex Interactions

Table 2.1. Percentage of Households Dependent on Indigenous Plant-based Coping Mechanisms at Kenyan and Tanzanian Site

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Provisioning services

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Regulating services

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Cultural services

Table 2.2. Trends in the Human Use of Ecosystem Services and Enhancement or Degradation of the Service Around the Year 2000 - Supporting services

Table 6.1. Prospects for Attaining the 2010 Sub-targets Agreed to under the Convention on Biological Diversity