L10 – Interactions between Plants and with Animals

Flashcards covering the ecological interactions between plants and animals in a pasture sward, including competition types, succession, resource management, and mutualism.

How is competition defined in the context of a pasture sward?

Competition is the negative effect of a plant on the growth, reproduction, and survival of another plant by consuming or controlling access to a particular resource.

What is the definition of succession in pasture ecology?

Succession is a change in the botanical composition of a sward over time, typically progressing from desirable species to undesirable species.

Which resources are plants primarily competing for above ground?

Above ground, plants compete for light and space.

Which resources are plants primarily competing for below ground?

Below ground, plants compete for nutrients and water, while roots also provide structural stability.

What is the difference between intraspecific and interspecific competition?

Intraspecific competition occurs between plants of the same species, while interspecific competition occurs between plants of different species.

Explain the concept of 'self-thinning' or density-dependent mortality.

Self-thinning is the trade-off where population density decreases as individual plant size (weight) increases, because the sward can only support a limited number of larger plants in a given space.

How does the light spectrum affect the tillering process in grasses?

Tillering is triggered by the ratio of red to infrared light; when a canopy is opened by grazing, more red light reaches the base of the plant, signaling it to tiller.

Why is ryegrass more suited to frequent, hard grazing than species with large tillers?

Ryegrass has relatively small, thin shoots and tillers, allowing it to capture light effectively even when maintained at a lower biomass.

What ecological advantage do legumes have over grasses in a nitrogen-limited environment?

Legumes have the ability to fix nitrogen ($N$), allowing them to thrive and contribute nutrients to the system while grasses rely on available soil nitrogen.

What is the carbon cost to a plant for nitrogen fixation via Rhizobia?

It costs the plant approximately $7.5\,g$ of carbon for every $1\,g$ of $N$ that is fixed.

How does the application of nitrogen ($N$) fertilizer typically affect a mixed grass-legume sward?

Adding $N$ generally favors the grass, increasing its tiller density, which can lead to the grass swamping or dominating the legume.

What is the difference between nutrient 'stratification' and 'patchiness' in a pasture?

Stratification is the bioaccumulation of nutrients in the top $5\,cm$ of soil over time, while patchiness refers to localized nutrient deposition from livestock urine and dung.

How does continuous grazing affect the persistence of chicory compared to rotational grazing?

Continuous grazing causes chicory levels to drop off dramatically because the plant lacks the recovery periods needed to restore root reserves.

What are the mutualistic benefits of mycorrhizal fungi for a plant?

The fungi produce fine hyphae that extend the root system to efficiently acquire nutrients like phosphorus ($P$) and zinc ($Zn$) in exchange for carbohydrates from the plant.

How do novel type endophytes provide a mutualistic benefit in pastures?

Novel endophytes reduce pest delivery by insects without causing the animal health issues associated with wild type endophytes, while the fungi derive nourishment from the plant.

What impact does soil drainage have on pasture yield and variability?

Well-drained soils typically produce higher yields with less variability, whereas imperfectly drained soils may suffer from waterlogging and reduced oxygen for root growth.