ANSWERS TO REVIEW QUESTIONS – CHAPTER 43
1.
In some Queensland rainforest communities there is synchronisation of flowering and insect
activity: peaks in the flowering of tree species coincide with peaks in the number of insects
in the same area. Explain why this may have evolved. (p. 1064)
There are two schools of thought among the scientists who have studied these communities. The first
group suggests that the communities have evolved together with very strong interactions. The other
group thinks that species with preferences for similar environmental conditions just happen to coexist
together.
2.
In a rainforest, many orchids, figs and ferns are epiphytes. What is an epiphyte and what
advantage is there to the tropical orchid in having this lifestyle? (p. 1069)
In a symbiotic relationship an epiphyte is an organism which benefits from the interaction without
affecting the other symbiont. In moist forests epiphytes are typically mosses, small ferns and orchids,
whereas in marine ecosystems, epiphytes are typically algae.
The tropical orchid may benefit from an association with a rainforest tree by obtaining a position closer
to light, by obtaining minerals and dissolved organic nutrients, and by obtaining protection.
3. What is the significance of ‘warning colouration’? Give an example. (p. 1074)
Among animals bold colours are thought to act as a signal to potential predators that the prey is
unpalatable or contains poisons that are distasteful. Predators learn to avoid distasteful prey by eating
one individual. An example of warning colouration is the monarch butterfly that consumes and
accumulates toxic compounds as a larva that then carry through to the brightly coloured adult.
4.
Why are mimics that are themselves non-toxic usually present in low numbers relative to
the distasteful species that they resemble? (p. 1074)
Mimicry relies on a colouration pattern in animals that do not posses toxins that resembles those that
are distasteful to predators. Since warning colouration works only when a predator learns to identify
distasteful prey through experience, a high proportion of mimics would result in little protection against
predation for both mimics and animals that do posses toxins or are unpalatable.
5.
How could species diversity in a community be determined by the activities of predators?
(p. 1075)
Species diversity in a community could be affected by the presence of keystone predators. Keystone
predators may target prey that dominate a particular ecosystem. Heavy predation of this prey allows for
other species to colonise areas in which they would normally be outcompeted. An example is the
predation of mussels by sea stars on rocky platforms in North America. These mussels outcompete
other intertidal species and a reduction in their density through predation allows other species, such as
barnacles and snails, to colonise and results in an increase in community diversity.
6.
Why is the sea star Pisaster ochraceus described as a ‘keystone predator’ on rocky shores of
the northwest coast of North America? (p. 1075)
Pisaster ochraceus is described as a ‘keystone predator’ because its presence or absence has a major
impact on the structure and diversity of the rocky shore community. Their predation on mussels has an
important effect on the intertidal community because mussels can exclude most other species. By
feeding on the mussels, the sea star provides clear areas which can be colonised by other species.
7. Define the term ‘succession’ and give an example. (pp. 1079–1081)
Succession is the gradual replacement of one community of species with another. An example of
succession is the sequence of plant communities that colonise and regenerate after wildfire, with r
strategists dominating early successional stages and K strategists dominating late successional stages or
climax communities.
8.
List four factors that can be called disturbances in communities. What is the intermediate
disturbance hypothesis? (pp. 1080–1082)
Fire, flood, drought in terrestrial ecosystems, and storm events in marine (reef damage) and terrestrial
(canopy wind-throw) ecosystems. ‘Novel’ human disturbances include vegetation clearance, urban
development and modified burning regimes.
The intermediate disturbance hypothesis suggests that community diversity will be maximised when an
intermediate disturbance regime occurs.
9.
Consider Figure 43.34. Why don’t the mangrove species B and C, which have a wide
tolerance range of salt, grow inland where species A occurs? (p. 1086)
Species B and C have higher salt tolerance but slower growth rates. Therefore, when conditions are
optimal species A will grow rapidly and colonise the inland regions within its salt-tolerance limits.
10. Explain the process (biotic and abiotic) that creates the patterns in community composition
on temperate Australian seashores. (pp. 1082–1083)
On the exposed rocky shores near Sydney, the communities of marine organisms form a mosaic.
Abiotic factors that contribute to this pattern include the degree of wave action and/or exposure to light,
which may vary according to the position taken by an organism. Biotic factors that influence the
mosaic are inter- and intra-specific competition and predation. Random disturbances also allow
different species to recolonise a patch.