The species to be investigated has to be identified. This is often easy,but may be difficult in some taxa, or in particular circumstances. For example, insect often require microscopic scrutiny, one species in a mixed flock of birds may be difficult to pick out and count accurately, and plant sometimes hybridise with other species, or occur as difficult taxonomic aggregates(see Section 6.2.5). The second problem is to decide what is an individual in the population. The bracken fronds in Figure3.1 (p.31),for example, are all members of one clone, that is one genetic individual, although they may look like a lot of separate plants.