Darker moths are less visible on the darker bark

During the industrial revolution in England, the moth population drastically changed from mostly white-coloured variants, to a majority being a darker black colour. This change in the peppered moth population was due to a change in their environment, as a result of increased pollution and smog.

Following the steps of evolution:

1. Within the natural moth population there is variation. Some 'mutants' were born with black bodies in a predominantly white-coloured population.

2. An environmental selection pressure was applied to the population. Due to the change in the environment being more polluted and smoggy, birds were better able to spot white moths as prey.

3. Most of the white moths were killed by predators, leaving black moths surviving within the population. The population is reduced for a few generations.

4. Because the black phenotype survive, they were able to reproduce and pass their colouring onto their offspring. As a result, over generations, black colouring became the dominant trait in the moth population.

Living resources and the interaction with the living parts of the ecosystem are referred to as biotic factors. The physical and chemical non-living resources and components are referred to as abiotic factors.

Biotic factors may include the following:

• Living organisms within the same ecosystem

• Competition for resources (e.g. food, territory)

• Predation

• Disease

Competition for resources: when Darwin visited the Galapagos Islands, he observed that a certain species of Finch with a short, strong beak lived on an island with nuts available as a food resource. For this species to have developed, there would have been an initial population of finches, perhaps with weaker beaks, who did not consume nuts.

Some finches were naturally born with a mutation of a stronger beak, and were able to crack open and consume nuts, as well as other more limited resources. As a result, these variants were able to consume more food, live longer, and pass their strong-beaked trait onto their offspring. As other food sources continued to deplete, these nut-eating birds survived, and over many generations became the dominant variant in the population.

Common biotic and abiotic factors

Introduction to Australia:

• • Cane toads are a native species of South and Middle America. They had been successfully introduced to Hawaii, increasing the yield of their sugar cane crops.

  • In 1935, the Bureau of Sugar Experiment Stations decided to introduce the species to Northern Queensland. This was in an attempt to control populations of native beetles eating sugar cane crops, the grey-backed cane beetle and the Frenchi beetle, without the use of harmful pesticides.

Spread:

• • Cane toads were released in a number of locations around Northern Queensland between 1935-36. they began to rapidly spread throughout the state, reaching the NSW border in 1978, and the NT border in 1984.

  • Cane toad populations have risen exponentially, with current estimates over 200 million.

  • This has resulted in widespread ecological effects, including the spread of disease and loss of local biodiversity. Their spread has been facilitated by travelling on clear roads, and 'hitch-hiking' with building and landscape materials.

Evolution:

• • Evolution is usually considered a slow and gradual process, taking place over millions of years, however it has been seen that the Australian cane toad population has rapidly changed over the past 70 years.

  • This is because of a phenomenon called 'spatial sorting'. Toads naturally born with longer legs move longer distances, and then breed with other toads who have also moved longer distances. The genes for faster movement become concentrated at the forefront of the invasion, being passed rapidly onto offspring. Tis has allowed rapid evolution over about 50 generations.

  • When they were first introduced, cane toads spread at a rate of 10km/year. Now, they spread at approximately 55km/year.

The typical daily travel distance of cane toads

Introduction to Australia:

• • Prickly pear originates from tropical and temperate regions of North and South America and the Galapagos Islands. It adapted quickly to Australia's diverse environments, including dry environments.

  • One species - smooth tree prickly pear - introduced into Australia from South America to establish a cochineal industry (dyes). In the early 1800s the pest prickly pear was introduced to farms for hedging/fencing and as a fodder reserve during droughts.

Spread:

• • By the 1870s the spread of prickly pear was starting to cause concern as its spread across eastern Australia was devastating to rural life.

  • By 1901 about four million hectares were affected in Queensland and NSW.

  • By 1925 this had grown to 24 million hectares and it was spreading at a rate of 400 000 hectares a year.

  • A large amount of time and money was invested to reduce the numbers of the plant. Early control measures included burning, crushing and the use of herbicides.

Population changes:

• • Prickly pear was successful invader because new plants established easily from seeds. The fruit, eaten by birds contains seed which remain viable for years. Pads broken off from the parent plant can survive for months because they contain a store of water and nutrients, even semi-digested pads are able to sprout.

  • Dense infestations hinder the growth and regeneration of native plants, particularly small shrubs and ground flora. This affects biodiversity.

  • Due to the lack of selection pressure, prickly pear plants had spread rapidly through the country. The only problem they faces was that the lack of selection pressure meant that there was a lack of diversity. Introducing a biological control provided such a strong selection pressure that worked with the limited diversity too quickly reduce the numbers and distribution of the plant.

Control:

• • Two species of insect were imported with the hopes of controlling the pest plant, the Cochineal beetle and Cactoblastis moth. The Moth showed the best results. By 1932, the larvae of the moth had eaten its way through three million of the previously infected hectares of land.

  • The eradication program was so successful other countries adopted the same method.