An isolated population of a small annual plant (without a seed bank) grows on a

Question

An isolated population of a small annual plant (without a seed bank) grows on a 700 m high, north-facing hillside in northern England. The other populations of this species occur in the mountains of Scotland and Scandinavia.

a) Outline three hypotheses to explain why this population survives on this isolated hillside.

Devise a set of b) observations and measurements, and c) experiments to assess whether this plant population would be able to survive a 3oC climate warming. In each case, also explain what analyses would be required to estimate whether survival was possible. Cost and assistance are unlimited, but the results must be delivered within five years.

b) Observations and measurements.

Explanation / Answer

a) _ Few hills in England are as high as 700 m (and most are in the north). If the population is restricted to high elevations, then it will experience cooler climatic conditions than most of the remainder of England.

_ North-facing hillsides in the northern hemisphere are cool because they receive reduced insolation; they fact away from the direct sun and are shaded by the hill. This will reduce average temperatures, and also reduce the xpected
maximum temperatures experienced.

_ High altitude and north-facing hillsides will experience reduced drought stress because of low evapotranspiration

b) Researchers would carry out a field surveys in years one to four, placing 10 replicated randomly located transects up-down the hillside. They would place 2m by 2m quadrats at 10 m elevation intervals along each transect (each individual quadrat centred up to 5 m left or right of the transect, at random). The number of
seedlings (in spring), mature plants (in summer), and seeds set per plant (from a random sample of 10 plants per quadrat) would be estimated for every quadrat containing the focal species. This would allow them to estimate the relationship between elevation and population density (potentially quadratic if the highest density is at intermediate elevation), and between elevation and the presence/absence of the species. The quadrats would be marked permanently.

It is known that average temperature tends to decrease with increasing elevation, according to the lapse rate (often around 0.55

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