sociopolitical and cultural factors
3.4 Environmental drivers
3.4.3 Pests, diseases and invasive alien species 22
Pests and diseases affect food and agriculture worldwide and can pose a threat to the supply of ecosystem services and to the survival of some components of BFA, particularly species or within- species populations confined to small geographi-cal areas. Aside from their direct effects, diseases can also threaten BFA indirectly, for example when their presence triggers practices such as
21 Citing bodmer et al. (2014).
22 the term alien species has been defined as “a species, subspecies or lower taxon, introduced outside its natural past or present distribution” and an invasive alien species as
“an alien species whose introduction and/or spread threaten biological diversity” (CbD, 2002).
the excessive use of pesticides, fire, antibiotics or tillage. Disease epidemiology is, in turn, affected by a range of drivers, including climate change, trade and changes in land use. Loss of biodiversity can itself be a risk factor (see Box 3.2).
Invasive alien species are regarded as a major threat to biodiversity (e.g. CBD Secretariat, 2006).
Alien species may be introduced into a new ecosys-tem accidentally, for example as a result of trade or travel (Wittenberg and Cock, 2001). However, they may also be introduced deliberately as part of various management measures, including for biological control purposes, and later turn out to be invasive (Myers and Cory, 2017). Ecological changes and imbalances caused by human actions can also contribute to invasions. For example, shrub encroachment by invasive thorny species is often a result of overgrazing (e.g. Kgosikoma and Mogotsi, 2013; see also Section 3.6.3).
Invasive species have had substantial impacts on various important components of BFA. For example, the New Zealand flatworm (Arthurdendyus box 3.2
Links between biodiversity, biodiversity loss and disease risk An increasing number of emerging infectious diseases in
humans, animals and plants have been reported over recent decades (Anderson et al., 2004; Fisher et al., 2012; Jones et al., 2008). This has been linked to rapid habitat changes caused by urbanization and agriculture intensification (Hassell et al., 2017). Empirical studies show that high levels of biodiversity are associated with high levels of pathogen diversity (Morand and Lajaunie, 2017). However, increases in epidemics and the risk of disease emergence are associated with decreased biodiversity (ibid.), as deforestation and agricultural intensification increase contacts between wildlife, domestic animals and humans, favouring the spread of zoonotic diseases (Keesing et al., 2010).
Empirical studies have also shown that species-rich host communities contribute to reducing the transmission of infectious diseases, a phenomenon known as the “dilution effect”. The effect has been observed in studies on several vector-borne and zoonotic diseases. A meta-analysis
of 90 studies on various diseases that affect humans, wildlife, livestock or plants concluded that they provide broad support for a negative effect of diversity on disease transmission (Johnson, Ostfeld and Keesing, 2015). The magnitude of the effect, however, appears to be related to the structure of species communities and not only to species diversity per se (Civitello et al., 2015).
Similar effects operate at the infraspecies (genetic) level. Species that have high genetic diversity may sustain a high diversity of pathogens, but with each pathogen showing low transmission and rarely causing an epidemic.
In contrast, while species that have low genetic diversity may sustain fewer pathogens, these pathogens may have high transmissibility and the potential to cause dramatic epidemics (Heesterbeek et al., 2015; Karvonen et al., 2016;
King and Lively, 2012).
Source: Provided by Serge Morand.
triangulates) is a significant threat to earthworms in the United Kingdom and some other European countries (Murchie and Gordon, 2013). Invasive plants may affect the abundance and community structure of mycorrhizal fungi or affect the leaf litter, and hence the habitats of litter-dwelling arthropods and other invertebrates (Cole et al., 2006; Jordan et al., 2012; Turbé et al., 2010). Invasive herbivores can influence soil ecosystems via their effects on the structure of plant communities (although not in all cases with a negative impact on soil biodiversity) (e.g. Bellingham et al., 2016; Stritar et al., 2010).
Numerous invasive species have had severe impacts on forests. For example, Hymenoscyphus fraxineus, a fungus that causes ash dieback disease, has been rapidly spreading across much of Europe (Forestry Commission, 2018). Ash dieback and the emerald ash borer (Agrilus planipennis), a beetle that is spreading westwards across Europe, are posing a major threat to ash tree (Fraxinus excel-sior) populations (Thomas, 2016). Loss of the ash would have a significant impact on biodiversity.
For example, 44 species in the United Kingdom (4 lichens, 11 fungi and 29 invertebrates) are table 3.10
Reported effects of pests, diseases and invasive alien species on the provision of regulating and supporting ecosystem services, by production system
Production systems (PS)
Effects of pests, diseases and invasive alien species on ecosystem services
Pollination Pest and disease regulation Water purification and waste treatment Natural-hazard regulation Nutrient cycling Soil formation and protection Water cycling Habitat provisioning Production of oxygen/ gas regulation
livestock grassland–based systems - - - +/- +/- -
+/-livestock landless systems +/- - - +/- - -
-Proportion of countries reporting
the Ps that report any effect of the
driver (%)
naturally regenerated forests - - -
-Planted forests - - -
-self-recruiting capture fisheries - - - 0 - -
-Culture-based fisheries - - - +/- - - 9–17
Fed aquaculture - - - +/- - - - 18–25
non-fed aquaculture - - - 26–33
irrigated crop systems (rice) - - - 34–41
irrigated crop systems (other) - - - 0 +/- -
-rainfed crop systems - - -
-Mixed systems - - - - 0 0 0 - 0
Notes: Countries were invited to report the effects (positive, negative or “no effect”) of this driver on the provision of each ecosystem service in each production system. If 50% or more of the responses for a given combination of production system and ecosystem service indicate the same trend (positive [+], negative [-] or “no effect” [0]) then this trend is indicated in the respective cell of the table. In other cases, mixed effects (+/-) are indicated. The colour scale indicates the proportion of countries reporting the presence of the respective system that report any effect of the driver(positive, negative or “no effect”) on the provision of the respective ecosystem service. See Section 1.5 for descriptions of the production systems and a discussion of ecosystem services. Analysis based on a total of 91 country reports.
Source: Country reports prepared for The State of the World’s Biodiversity for Food and Agriculture.
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considered “obligate” ash-associated species and a further 62 (19 fungi, 13 lichens, 6 bryophytes and 24 invertebrates) to be highly associated with the ash (Mitchell et al., 2014).
Many aquatic ecosystems are also affected by invasive alien species, which can cause problems, inter alia, by preying on native species, impeding watercourses and affecting ecological processes such as nutrient cycling (MEA, 2005b). Major examples include water hyacinth (Eichhornia crassipes), a highly invasive species that covers and chokes major waterways and lake surfaces in many countries, negatively affecting biodiversity, fisheries, hydroelectric production, transportation and local economies across large parts of Africa and Asia (CABI, 2018).
Information provided by countries on the effects of pests, diseases and invasive alien species on the supply of ecosystem services is summarized in Table 3.10. The ecosystem services most often reported to be negatively affected are pollination, pest and disease regulation and habitat provision-ing. Several countries report that invasive species and/or pests and diseases are becoming more prev-alent, with a number noting that climate change, habitat destruction or changes in agricultural practices are exacerbating factors (see below for further information). Some provide specific exam-ples of the effects of pests, diseases and invasive alien species on associated biodiversity and the supply of ecosystem services. For instance, Zambia reports that invasive alien species have nega-tively affected the habitats of some pollinators.
The Bahamas mentions that the lionfish (Pterois volitans), an invasive species that entered the country’s waters in recent years, is a threat both to biodiversity and to fisheries. More specifically, it notes that as well as feeding on the juveniles and adults of commercially important fish species such as grunts and snapper, the lionfish is feared to be affecting coral reefs by predating on herbi-vores that keep the reefs free of algae. In order to counteract the impact of the lionfish, the country’s Fisheries Department is introducing initiatives to encourage the consumption of the species (see Section 4.4 for additional information).
Sri Lanka reports that the clown knife fish (Chitala ornatus), first introduced as an ornamental aquar-ium fish, is affecting some of the county’s most threatened endemic freshwater fish populations.
The Netherlands mentions that the Pacific oyster (Crassostrea gigas), an invasive alien species that has been spreading through the country’s waters since the 1960s, is considered a serious threat to the functions of coastal waters, including shellfish culture and the provision of feeding areas for birds.
It notes, however, that reefs created by this species can provide an important habitat for certain spe-cies.23 A few countries mention the threat posed by hybridization between invasive alien species and native species. For example, Zambia reports that the Nile tilapia (Oreochromis niloticus), an escapee from fish farms, is not only competing with indig-enous fish but also likely to be altering the genetic composition of native cichlid species.
Countries were invited to report examples of invasive alien species that had had a significant effect on BFA and/or ecosystem services in the preceding ten years. The 59 countries24 that responded reported a total of 1 077 such cases, involving 633 distinct species and 509 distinct genera. The most commonly reported species are shown in Table 3.11. Half of the reported invasive alien species are plants, 46 percent animals, and the remaining 4 percent fungi, chromists, viruses or bacteria (Figure 3.3). Almost 60 percent are reported by Asian or European countries.
With regard to the causes of species inva-sions, some country reports, as noted above, mention a link to climate change, for example in the case of the threat posed by Kikuyo grass (Pennisetum clandestinum) to the páramo
23 the report cites smaal, Kater and Wijsman (2009).
24 angola, argentina, bangladesh, belarus, belgium, bulgaria, burkina Faso, Cameroon, China, Cook islands, Croatia, ecuador, egypt, el salvador, estonia, eswatini, ethiopia, Fiji, Finland, France, Gambia, Grenada, Guyana, Hungary, india, iraq, ireland, Jordan, Kenya, lebanon, Mali, Mexico, nepal, netherlands, niger, norway, Palau, Panama, Papua new Guinea, Peru, Poland, Qatar, samoa, saudi arabia, slovakia, slovenia, spain, sri lanka, sudan, sweden, switzerland, togo, tonga, united Kingdom, united states of america, viet nam, Yemen, Zambia, Zimbabwe.
table 3.11
Invasive alien species reported by five or more countries as present in one or more production systems Production systems where reported
(in decreasing order of frequency) Impact on BFA
countries Negative Neutral Positive Negative Neutral Positive
Eichhornia
crassipes Water
hyacinth 21
self-recruiting capture fisheries, culture-based fisheries, irrigated crop systems (rice), mixed systems (livestock, crop, forest and/or aquatic and fisheries), fed aquaculture, irrigated crop systems (non-rice), non-fed aquaculture, livestock grassland-based systems, naturally regenerated forests, planted forests, rainfed crop systems
14 0 3 13 1 3
Lantana camara largeleaf
lantana 14
livestock grassland-based systems, naturally regenerated forests, irrigated crop systems (rice), planted forests, irrigated crop systems (non-rice), mixed systems (livestock, crop, forest and/or aquatic and fisheries), rainfed crop systems, livestock landless systems
10 1 1 6 0 1
Cyprinus carpio Common
carp 10 self-recruiting capture fisheries, fed aquaculture 5 1 1 4 1
Prosopis juliflora ironwood 10
naturally regenerated forests, livestock grassland-based systems, irrigated crop systems (non-rice), irrigated crop systems (rice), mixed systems (livestock, crop, forest and/or aquatic and fisheries), planted forests, rainfed crop systems
7 0 2 5 0 2
Mikania
micrantha bitter vine 9 naturally regenerated forests, livestock grassland-based systems, irrigated crop systems (rice), livestock landless
systems, mixed systems, planted forests, rainfed crop systems 4 0 3 3 0 2 Chromolaena
odorata siam weed 9
naturally regenerated forests, planted forests, livestock grassland-based systems, irrigated crop systems (rice),
livestock landless systems, rainfed crop systems 5 0 2 4 0 2 Oreochromis
mossambicus Mozambique
tilapia 8 self-recruiting capture fisheries, culture-based fisheries, fed
aquaculture 6 0 0 2 1 0
Parthenium
hysterophorus santa-Maria 8
livestock grassland-based systems, naturally regenerated forests, mixed systems (livestock, crop, forest and/or aquatic and fisheries), planted forests, rainfed crop systems, irrigated crop systems (non-rice), irrigated crop systems (rice), livestock landless systems
5 0 3 3 0 3
Harmonia axyridis Harlequin
ladybird 7 rainfed crop systems, irrigated crop systems (non-rice), livestock grassland-based systems, mixed systems (livestock, crop, forest and/or aquatic and fisheries), planted forests
5 0 0 1 0 0
Salvinia molesta Giant salvinia 7
irrigated crop systems (rice), self-recruiting capture fisheries, culture-based fisheries, fed aquaculture, mixed systems (livestock, crop, forest and/or aquatic and fisheries), rainfed crop systems
5 0 1 4 0 1
Bemisia tabaci sweet potato
whitefly 6 rainfed crop systems, irrigated crop systems (non-rice),
irrigated crop systems (rice) 2 0 2 2 0 1
Micropterus salmoides
largemouth
bass 6 self-recruiting capture fisheries 5 0 0 1 0 0
Oncorhynchus
mykiss rainbow
trout 6 Fed aquaculture, self-recruiting capture fisheries 4 0 0 1 1 0
Oreochromis
niloticus nile tilapia 6 self-recruiting capture fisheries 3 0 1 3 0 0
(Cont.)
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the state of the WorlD's bioDiversit y for fooD anD agriculture Production systems where reported
(in decreasing order of frequency) Impact on BFA
countries Negative Neutral Positive Negative Neutral Positive Pistia stratiotes Water lettuce 6
self-recruiting capture fisheries, culture-based fisheries, irrigated crop systems (rice), mixed systems (livestock, crop, forest and/or aquatic and fisheries), naturally regenerated forests
3 0 1 3 0 1
Tuta absoluta tomato
leafminer 6 irrigated crop systems (non-rice), rainfed crop systems,
irrigated crop systems (rice), naturally regenerated forests 1 0 1 0 0 1 Leucaena
leucocephala White
leadtree 6
Mixed systems (livestock, crop, forest and/or aquatic and fisheries), naturally regenerated forests, livestock
grassland-based systems 3 0 0 3 0 0
Merremia peltata Merremia 5 naturally regenerated forests, mixed systems (livestock, crop,
forest and/or aquatic and fisheries) 3 0 0 1 0 0
Ambrosia
artemisiifolia Common
ragweed 5 rainfed crop systems, irrigated crop systems (non-rice), mixed
systems (livestock, crop, forest and/or aquatic and fisheries) 3 0 1 2 0 0 Ceratitis capitata Medfly 5 rainfed crop systems, irrigated crop systems (non-rice), mixed
systems (livestock, crop, forest and/or aquatic and fisheries) 1 0 0 1 0 0 Cherax
quadricarinatus australian
redclaw 5 self-recruiting capture fisheries 5 0 0 2 0 0
Clarias gariepinus north african
catfish 5 self-recruiting capture fisheries, fed aquaculture 4 1 0 2 2 0
Heracleum mantegazzianum
Giant
hogweed 5
rainfed crop systems, mixed systems (livestock, crop, forest and/or aquatic and fisheries), livestock grassland-based systems, irrigated crop systems (non-rice), naturally irrigated crop systems, planted forests
4 0 0 2 0 0
Pacifastacus
leniusculus signal crayfish 5 self-recruiting capture fisheries, fed aquaculture,
culture-based fisheries, non-fed aquaculture 3 0 0 2 0 0
Fallopia japonica Japanese
knotweed 5
naturally regenerated forests, planted forests, mixed systems (livestock, crop, forest and/or aquatic and fisheries), irrigated crop systems (non-rice), livestock grassland-based systems, rainfed crop systems
4 0 0 2 0 0
Robinia
pseudoacacia black locust 5 naturally regenerated forests, irrigated crop systems (non-rice), planted forests, mixed systems (livestock, crop, forest
and/or aquatic and fisheries) 1 2 1 3 0 1
Solidago
canadensis Common
goldenrod 5
Mixed systems (livestock, crop, forest and/or aquatic and fisheries), rainfed crop systems, livestock grassland-based systems, irrigated crop systems (non-rice), naturally irrigated crop systems, planted forests
2 2 0 3 0 1
Solidago gigantea tall goldenrod 5
Mixed systems (livestock, crop, forest and/or aquatic and fisheries), rainfed crop systems, irrigated crop systems (non-rice), livestock grassland-based systems, naturally irrigated crop systems
3 1 0 3 0 1
Varroa destructor varroa mite 5 rainfed crop systems, livestock grassland-based systems, irrigated crops (other), mixed systems (livestock, crop, forest
and/or aquatic and fisheries), planted forests 4 0 0 2 0 0 Note: Analysis based on a total of 91 country reports.
Source: Country reports prepared for The State of the World’s Biodiversity for Food and Agriculture.
table 3.11 (Cont.)
Invasive alien species reported by five or more countries as present in one or more production systems
FiGure 3.3
Invasive alien species reported by countries to be impacting biodiversity for food and agriculture, (A) by type of organism and (B) by region
Chromists 2%
Plants 50%
Other arthropods 1%
Insects 16%
Crustaceans 2%
Ray-finned fish 12%
Birds 3%
Molluscs 4%
Other animals 3%
Fungi 2%
Mammals 5%
0 50 100 150 200 250 300 350
A
B
Number of responses Pacific
North America Near East and North Africa Latin America and the Caribbean Europe and Central Asia Asia Africa
Notes: A “response” is a mention by a specific country of a specific component of biodiversity (species or genus). Out of 91 reporting countries, 59 provided a combined total of 1 077 responses. A single species or genus may be reported by more than one country.
Source: Country reports prepared for The State of the World’s Biodiversity for Food and Agriculture.
ecosystem in Ecuador. Zimbabwe mentions that heightened climatic variability, including floods and droughts, are increasing susceptibility to inva-sive species, with negative impacts on, inter alia, wild foods. Mexico refers to a number of human actions (e.g. modernization of transport systems, mining, biological control practices and artificially joining water bodies) and natural phenomena
(e.g. natural disasters) as contributing to the intro-duction of invasive species.25 Palau reports that, in the last 20 years, land clearing, road construction and other human activities have enabled the inva-sive vine Merremia peltata to thrive.
25 the report cites Comité asesor nacional sobre especies invasoras (2010).
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the state of the WorlD's bioDiversit y for fooD anD agriculture