Ecological Basis of Agriculture

Ecological Basis of Agriculture: Definition

• Ecologists and agronomists are combining to address food production systems, forming the field of agroecology.

How Agriculture Relates to Ecology

• Agricultural systems are collections of organisms that follow ecological principles such as competition and food webs.
• The soil ecosystem is complex and vital to agriculture.
• Human intervention in agriculture is extreme, resulting in practices like monocultures and suppression of natural processes.
• There is high emphasis on replacing minerals in an artificial form.

Ecological Problems and Solutions

• Focus on yield leads to:
  • Resource removal from the system.
  • Plants and animals bunched, causing pests and disease.
  • Impoverished biotic interactions.
• Replacing natural functions:
  • Resource inputs have impacts.
  • Chemicals to control pests contaminate and create resistance.
  • Natural enemies do not yield.
• Modern agricultural practices are hard to sustain without wider costs.

Parasites

• Parasites of grazing livestock have a high biodiversity in livestock monocultures.
• Examples include nematodes like Ostertagia ostertagi and Platyhelminths like cestodes and trematodes.

Ostertagia ostertagi: Nematode Example

• Ostertagia ostertagi is a slender, red-brown nematode ≤ 1 cm long.
• Adults live on the surface of the abomasal (stomach) mucosa.
• Parasites develop in the gastric gland.
• HCl production is reduced and pH rises, preventing pepsinogen from cleaving to pepsin.
• This results in structural changes to the gastric mucosa.
• There is protein movement from blood to lumen, called protein-losing gastritis.
• Clinical signs include diarrhoea, anorexia, emaciation, and death.
• Most signs are sub-clinical, with weight loss and reduced milk yield, known as protein-losing disease.
• The life cycle for the nematode includes:
  • L3 exsheaths in rumen and development to Adult in abomasal gland.
  • After 18 days adult emerges.
• Transmission is density-dependent.
• Density dependence regulates red grouse populations by the nematode Trichostrongylus tenuis.
  • Worm treatment prevents population crashes, which suppresses cycles.
• Parasite impacts are more severe when dispersal is constrained.
• Hosts adapt to evade parasites through migration, shown in the saiga antelope Saiga tatarica.
• Roe deer numbers crash in fenced forest fragments.
• Higher stocking density means less grazing dispersal, resulting in parasite intensification.

Parasite Control

• Parasite impacts depend on infection intensity, with higher density resulting in more infections.
• Parasitic infections are problems of grazing intensification, necessitating solutions.

Options for Control:

• Prevention: using anthelmintics to suppress egg output, but it selects for resistance.
• Chemo-prophylaxis involves treating the group with anthelmintic drugs during grazing season.
  • About 90% of sheep harms have anthelmintic resistance.
• Evasion: physically separating via strategic grazing.
• Avoid grazing contaminated pasture at peak times.
• Dilution: pasture sharing.
• Decreasing contamination via stocking density, but implies reduced yield.

Ecology in Liver Fluke

• The liver fluke Fasciola hepatica has a sheep definitive host and snail intermediate host.
• There is contamination of pasture with infective metacercariae.
• The acute phase causes damage to liver during migration.
• The chronic phase results in blood loss from feeding.
• Sudden death in sheep can occur in autumn, while chronic aneamia occurs in the winter.
• Flukey land has wet conditions.

Parasite Summary

• Parasite control in gazing livestock is difficult without biocides due to high host density, lack of dispersal and land availability.
• Control is restored through better land use, more grazing management, and ecological control.
• Ecosystem pest control via grasses and grazers.
• Habitat heterogeneity results in reduced grazing on flood prone areas.
• Mixed species grazing has some benefits, since it involves refractory hosts.
• Sciomyzid flies eat fluke-carrying snails, reducing fluke infections.
• Nematophagous fungi reduces nematodes.

Pest Control

• Birds, spiders, flies and beetles all work together.
• Some ecosystem services are pollination via bees, and nutrient cycling done by dung beetles.
• Crop pest control can be extended to grazing livestock through managing ecosystems, reducing diversity and increasing density.
• Protection from predators increases parasite risk since necessary chemical control often fails.
• Farmers that aim to use ecosystem services, face challenges, with production benefits trading off against yield.
• Production benefits often trade off against yield.
• Biodiversity is a farm service subsidized by wider society.