There is a lot of attention in the media on the different environmental problems our planet is facing and that they will ultimately result in the extinction of many species.

However, what many people have to realise is that with respect to biodiversity this situation has already started and many populations of animals are declining. This article serves to highlight why these animals that serve important functions in our ecosystems are disappearing.

The most popular animal in the news in terms of declining populations is the honey bees, referred to as Colony Collapse Disorder (CCD) which occurs when the worker bees in a hive disappear abruptly.

However, the presence of dead honey bees in the hive or at the entrance is not an indication of CCD. Usual symptoms that a hive has CCD is the presence of food stores such as honey and pollen that have not been robbed by other bees, as well as by the presence of capped brood in abandoned nests. Capped brood is when the larvae develop into pupae the stage before adulthood, and the worker bees seal or cap the top of the area (cell) they are in. However, they would not abandon the hive until all of the brood have hatches. Also the presence of the queen bee in abandoned colonies: if she is not present, then the death of the colony would be attributed to the death of the queen.

In colonies affected by CCD, there would not be enough workers to maintain the hive. Also the workforce would be comprised mainly of young adults and those workers that are alive would be reluctant to feed and thus bring back resources to the nest. All of these factors can be taken as precursor symptoms to the final collapse of the colony.

Many causes for CCD have been proposed and include poisoning from the application of general pesticides to crops or to hives to control mite pest populations. Another reason may be due to disease, which in this case is the Varroa mite, or other emerging diseases like the gut parasite Nosema and the Israeli Paralysis virus.

Modification of the habitat can also be a factor in that the bees do not get enough food, or it may be a combination of factors.

Other groups of animals whose populations have been on the decline include butterflies. The monarch butterfly in particular. The orange and black pattern of the Monarch butterfly could be one of the best known in terms of nature and regarded as iconic. In 2009 a study of migrating populations showed that the number of females decreased by 10% in the ten year period 1975 to 1985. However in 2008 only 35% of the butterflies sampled were females. Also there is a decline in the number of females along the migratory route. A possible explanation for this is global climate change therefore the rise in temperature works against this species as it depends on the cold to act as a cue to indicate when it is time to migrate.

Monarch butterflies depend on the milkweed plant for food in the caterpillar stage so that the females lay their eggs on the plant. So another possible cause could be the presence of a tropical milkweed species which does not die back during the winter, so again the butterflies do not receive the signal that it is time to migrate. Hence the constant presence of this plant may result in the females staying back to lay their eggs rather than enter the migratory pool.

The final possible explanation is the presence of the parasitic protozoan Ophyryocystic elecktrioscirrha, which has a higher success in killing off females than males. Simply put this means that less females are available to reproduce and lay eggs and continue the population.

Turning to vertebrates, amphibians are an example of a group of animals that have suffered dramatic decline in population numbers which have been observed since the 1980's, all over the world.

With respect to amphibians, which include frogs, toads, newts and salamanders and caecilians, this group of animals are particularly sensitive to the factors that cause population declines. This sensitivity is due to the fact that their skin is very permeable so that any toxins are readily absorbed, for instance the aquatic fungus Batrachochytrium dendrobatidis. Toxins from pollution can cause deformities such as extra limbs and malformed eyes, while others affect the central nervous system.

Levels of hormones such as oestrogen in the water are believed to result in an increase in the number of females.

However, other potential causes for decline in amphibian populations include fungi like are affected by many other environmental problems, such as, ozone depletion. Ultraviolet-B (UVB) radiation causes harm to the DNA of amphibians in particular their eggs.

Amphibians produce photolysis which is an enzyme that protects them from UVB radiation however; some amphibians like frogs produce this in fewer quantities. So without the depleting protective ozone layer amphibians may not become extinct but it can cause sublethal damage.

Also amphibians spend part of their life cycle in the water and part on land so any toxins, or parasites present in either type of ecosystem will affect this group of animals. Because of their sensitivity, it is believed that they can be used as indicator species with respect to environmental threats.

It is hoped that this article has woken up many people that the effects of environmental problems, such as habitat change, loss and fragmentation, global climate change and ozone layer depletion are just some of the causes of declining animal populations.

This is detrimental in that some of these animals like bees and butterflies perform important functions in ecosystems such as pollinators of crop species.