Read the text. For questions 6.1.–6.4., choose the appropriate paragraph and write the corresponding letter (A–E) in the table. One paragraph does not match any of the questions.

 

In which paragraph does the author

6.1.	describe the way lesser flamingos extract sustenance from water?
6.2.	refer to an exhausting activity which makes lesser flamingos’ colour fade?
6.3.	mention a combination of factors that prevent numerous species from living in the environs of Lake Natron?
6.4.	point to lesser flamingos’ competitive advantage in terms of obtaining food from Lake Natron?

 

HELL ON EARTH

A. Located in the vicinity of volcanic springs and caustic alkaline waters in northern
Tanzania, Lake Natron is a most unusual ecosystem. Its pink water has a crust, it is
unnaturally hot; and because of the chemicals it feels as if someone has poured in a lot of
soap. Limited oxygen, copious salt and scorching heat is a deadly mix which means most
animals cannot survive there but, remarkably, the hellish conditions are actually highly
productive for some species that have adapted to cope with the harsh environment.
The organisms in and around Lake Natron benefit from a plentiful food supply, abundant
space and a tranquil environment.

B. High temperatures and mineral rich water are perfect for microscopic cyanobacteria.
When these micro-organisms bloom, they colour the lake. Depending on their
concentration, it may appear pink, red or orange. Only three fish species, different types
of cichlids, can survive in the lake. Researchers believe they evolved from a single
species 10,000 years ago, when Lake Natron’s conditions are thought to have worsened.
Cichlids, which feed on cyanobacteria, have the highest recorded metabolic rate of any
fish and can deal with the low oxygen levels in the water by coming to the surface to
breathe.

C. Cichlids are prey for many birds; but most avian predators cannot spend large amounts of
time in the toxic water because it will burn their skin. However, there is one resident
species whose tough and leathery skin enables them to feed in the lake for much of
the day – the lesser flamingo. Three quarters of these birds start their life at Lake Natron.
High salinity produces immense cyanobacterial blooms so food is abundant and rivals are
scarce.

D. Walking through the shallow water, the flamingos stop, lower their heads and filter feed.
Taking in the dirty water, they force it out of their beaks through a fine mesh which retains
their prey, loaded with the beta-carotene that gives the lesser flamingos their distinctive
pink colouration. During the dry season the lake reduces in size, revealing remote mudflat
islands, which are ideal for nesting flamingos. As breeding space increases, more and
more flamingos congregate, ensuring one of the most captivating spectacles of the
natural world – the pink parade, which is the biggest wildlife event on Natron’s calendar.

E. When the eggs hatch, the parents begin feeding their chicks with crop milk.
The energy-rich food is made in the adults’ throats and its production is such a drain on
them that they start to lose their pink colouration. The birds breed once every five years,
so they have ample time to regain their energy before taking part in another pink parade.
The lake may be described by some as hell on Earth but for cyanobacteria, cichlids and
lesser flamingos, it is heavenly.

Adapted from: BBC Wildlife