BD 1

BACKGROUND 

• Bodiversity is the variety of all life forms on earth - the different plants, animals and micro-organisms and the ecosystems of which they are a part. 

• Biodiversity is important to balance the Earth’s ecosystems. Biodiversity can be affected slowly or quickly over time by natural selective pressures. Human impact can also affect biodiversity over a shorter time period. In this module, students learn about the Theory of Evolution by Natural Selection and the effect of various selective pressures.

• Monitoring biodiversity is key to being able to predict future change. Monitoring, including the monitoring of abiotic (non-living) factors in the environment, enables ecologists to design strategies to reduce the effects of adverse biological change. Students investigate adaptations of organisms that increase the organism’s ability to survive in their environment.

• Australia is home to between 600,000 and 700,000 species, many of which are found nowhere else in the world. 

BIOTIC FACTORS

Biotic factors in an ecology can be classified into 3 groups:

1. Producers (autotrophs) - usually green plants that carry out photosynthesis to produce food.

2. Consumers (heterotrophs) which directly or indirectly depend on the photosynthetic output of the primary producers. There are three groups of consumer: primary consumer, secondary consumer and tertiary consumer.

3. Decomposer (detritivores) such as bacteria and fungi that carry out decomposition, the breakdown of the remains of dead organisms including animal waste products into simpler inorganic substances to be used by plants

Species are interconnected in many ways within an ecosystem, some that are too subtle to be immediately identified. 

Yellowstone National Park Case Study

Following is a video that shows how not understanding the role of a species in an ecosystem can lead to unanticipated and sometimes disastrous consequences. 

The wolf, as became apparent, is a keystone species in Yellowstone National Park in America. A keystone species is a species that has a much larger effect on its natural environment than would be expected for its numbers. These species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in the ecosystem and helping to determine the types and numbers of various other species in the community. 

The name keystone species comes from the role of a keystone (middle stone) in an arch. While the keystone is under the least pressure of any of the stones, the arch will collapse without it. Similarly, an ecosystem may experience a dramatic shift if a keystone species is removed, even though that species was a small part of the ecosystem by measures of numbers (biomass) or productivity (how much they contributed).

Selection Pressures

Environmental selection pressures are external factors that affect an organism’s ability to survive in its environment. 

Selection pressures drive evolution:

In any population some individuals will have genetic traits (eg a colour that helps them blend into their surroundings and be harder to see, therefore safer from predators) that make them better suited to the environmental conditions of their habitat, and give them a greater tolerance towards changes in the environment. They will have a survival advantage over others not having that trait, or not having it to the degree. They will be more likely to reproduce and pass on these favourable traits to their offspring. Those less suited are less likely to survive and successfully reproduce, and pass on their genes to the next generation. This is the process of evolution by natural selection. 

Selection pressures can:

•  be negative - decrease the number with a genetic trait (eg black peppered moths on a white tree) 

• be positive - increase the number with a genetic trait (eg white peppered moths on a white tree)

• change, leading to changes in what is a beneficial adaptation (tree darkens with pollution, now black is beneficial)

• be affected by population size (eg amount of food available)

• be unaffected by population size (eg floods)

Types of selection pressures that influence the size, growth, and distribution of a population  include:

• Biotic - Biological factors – predators,  pathogens (diseases), presence of sufficient food, availability of mates

• Abiotic - Environmental conditions – temperature, wind, climate, sunlight, rainfall, soil composition, natural disasters, pollution. 

i) Predator-Prey Case Study: Canada Lynx and Snowshoe Hare

The relationship between the Canada lynx (Lynx canadensis), sometimes called Canadian lync, and the snowshoe hare (Lepus americanus) is considered a classic example of how interactions between a predator and its prey can influence population changes in the two species. Canada lynx populations rise and fall with rises and falls in populations of snowshoe hares. When hares are abundant, lynx populations expand, and when the number of hares is reduced, lynx are forced to hunt squirrels, grouse and foxes. The shift away from hares takes its toll, and lynx populations ultimately shrink. 

Although this relationship was observed and reported over 200 years ago, and numbers were counted from the 1840s to 1930s, it was not until 2009 that the reason for the drop in hare population was really understood. 

A study tested the effects of stress on snowshoe hare reproduction. When wild caught pregnant hares held in a pen were exposed to a dog for just a couple minutes every other day,  both number and size of offspring decreased. The pregnant females used in the experiment and the pregnant females sampled in the wild, which were in the midst of a population decline, were found to produce high levels of the hormone cortisol, a substance produced by animals under stress.

For the Canada lynx, the more hares the better, but that ultimately translates into more stress for hares and a downward spiral in their populations. 

ii) Pathogens (disease)

John Haldane, a pioneer in genetics, was among the first to propose that infectious diseases, a major threat to human populations, had been acting as a powerful selective pressure and may be considered a major driver of evolution in our species. 

There is a high prevalence of the genetic condition alpha thalassemia in the Mediterranean basin. People with an inherited blood disorder called alpha thalassemia make unusually small red blood cells that mostly cause a mild form of anemia. 

When these smaller blood cells were found to provide an advantage against malaria, Haldane suggested that the large number of people with alpha thalassemia was the result of a selective pressure brought about by the disease.  

It was not until the availability of large-scale genetic data and the development of new methods to study molecular evolution that we could assess by how much infectious agents have shaped our genetic material. A recent analysis has indicated that among the diverse environmental factors that most likely acted as selective pressures during the evolution of our species (climate, diet regimes, and infections), pathogen load had the strongest influence on the shaping of human genetic variation.  

iii) Availability of Food 

Consider the effect on the population of the Canadian Lynx in response to numbers in the Snowshoe Hare population, as discussed earlier. 

iv) Availability of Mates

Case Study in a frog species: 

Female mate choice influences the evolution of male courtship signals and may promote formation of new species. Conducting experiments on a population of the Amazonian frog Engystomops petersi in the location of Puyo, Ecuador. Female frogs from Puyo strongly discriminate against the male frogs from La Selva because the male La Selva frogs do not make a squawk noise in their mating signals, but males from Puyo do. Over time, mutations that occur in the Puyo frogs wil not be shared with the La Selva frog population, and through this sexual selection pressure, the two populations will drift so far that they will become separate species. 

ABIOTIC FACTORS

Abiotic factors are non-living factors in an ecosystem. Although they are not living themselves, as part of the ecosystem, these factors do affect the living things in it. Abiotic factors make up for much of the variation seen between different ecosystems. By determining the availability of such essential resources as sunlight, water, oxygen, and minerals, abiotic factors determine which organisms can survive in a given place. 

Human activities have an immense impact on almost every habitat - increasing atmospheric CO2, altering soil structure, polluting water bodies.

Background

Sugar cane had been commercially grown in Queensland since the 1860s and losses caused by white grub attacks began to be a serious problem in the 1880s. The grubs — the larvae of up to 13 different species of native beetles — eat the roots of the cane, causing the plants to die. The problem was significant enough for the Queensland government to bow to pressure from canegrowers and establish the Queensland Bureau of Sugar Experiment Stations (BSES) in 1900. By 1935, entomologists employed by BSES had been studying the biology of the cane beetles and investigating solutions to their impacts for around 25 years.

Plenty of good science was produced during this time — the life cycles of several beetle species were described and an understanding of their biology and ecology had been worked out enabling more focused control measures. Many field and lab trials were done in a bid to develop effective controls including the use of various chemical insecticides, soil-fumigation methods, biocontrols such as parasitic fungi and native insects, physical removal methods, and agricultural and cultivation practices. Some of these showed promise but were prohibitively expensive or not readily available, and others were simply not effective.

The introduction of cane toads (Bufo marinus) to Australia in the 1930s is one of the foremost examples of an exotic animal release gone wrong. Originally imported from Hawaii and released in Queensland as a biological control for beetle pests of sugar cane, the cane toad is now a well-established pest itself. Cane toads currently range across Queensland, the Northern Territory and into New South Wales and Western Australia. Despite being less widespread than foxes or rabbits, community surveys consistently rank the toad as our most hated invasive animal and it is listed as a key threatening species under the Environment Protection and Biodiversity Conservation Act 1999. 

How it happened

A government entomologist working for BSES, Reginald Mungomery, imported the toads, bred them and released them. He was convinced the cane toad was the answer to a major agricultural crisis in the sugar industry, as they had reportedly solved similar beetle problems in Hawaii, the Philippines and Puerto Rico.

In 1932, a paper was presented by a woman named Raquel Dexter at the 4th Congress of the International Society of Sugar Cane Technologists in Peurto Rico on the use of Bufo marinus as a biological control for beetle infestations in sugar crops there. The toad was subsequently taken from Peurto Rico to Honolulu to control beetle infestations in Hawaiian sugar cane fields. In June 1935, Mungomery travelled to Hawaii where he captured 102 toads and brought them back to Australia. When he arrived at the Meringa experimental farm near Gordonvale in far north Queensland on 22 June 1935, all but one toad had survived the journey. The toads were housed in a purpose-built enclosure and left to breed. On 19 August that year, 2400 toads were released into sites around Gordonvale. In less than two months the number of toads had increased at least 24-fold. Further releases of toads in the Cairns and Innisfail areas soon followed.

Opposition

Another Australian entomologist, Walter Froggatt, voiced concerns about the release around this time, writing prophetically ‘this great toad, immune from enemies, omnivorous in its habits, and breeding all year round, may become as great a pest as the rabbit or cactus’. He lobbied the federal government to exercise caution and the Director-General of Health banned any further release of toads in December 1935. But this ban was to be short lived. BSES and local cane growers subsequently lobbied the Queensland Premier and Minister for Agriculture, who in turn pressured the Prime Minister Joseph Lyons, who rescinded the ban in September 1936. Toads were then released throughout the sugar cane regions of Queensland.

Shortfalls in risk assessment

As reported by Griggs, ‘all the cautious testing characterising the previous investigations into cane grub control methods was completely forgotten when it came to the cane toad. There is no evidence of any pre-release testing by the BSES entomologists to determine if the toads even ate the cane beetles’. The extremely short timeframe between the toads arriving in Australia and the first release supports this. The beetles that the toads were supposed to control were native Australian species, different to those causing problems in Hawaii and Peurto Rico, yet no trials were carried out to see if this translated to Australian conditions. Risk assessments of potential harms from the introduced species were not done.

It is not surprising that cane toads were imported and released with apparently little-to-no checks or control measures in place. Colonial Australia had a rich history of acclimatisation societies and settlers who introduced foxes, rabbits, deer, blackberries and other species in the 1800s, mainly for food, hunting, or the purpose of making the new country feel more like mother England. Acclimatisation societies were viewed as scientific organisations and were the precursor to many zoological societies that still exist today. Quarantine was a state responsibility in the early 1900s and mainly focused on human health, with animal health only coming into focus after the second World War.

The cane toad was first recognised as a pest in Western Australia where it was listed as vermin under the state’s Vermin Act in 1950. No serious attempts were made to raise cane toad control as a national issue until the early 1980s. The Commonwealth first took some responsibility for the problem in 1986, with federal funding and establishment of a cane toad Research Management Committee.

Conclusion

There is little doubt that those involved believed they were doing the right thing by importing and releasing the cane toad. Despite warnings from other scientists, appropriate pre-release testing of potential impacts was not done and initial control measures were overturned in the face of industry pressure. It is likely that the lessons from the cane toad debacle have influenced the strict quarantine laws and risk assessment procedures Australia has in place today.

The prickly pear had a devastating impact on life in rural eastern Australia during the early part of the 20th century. The story started over two hundred years ago…

Read article: Fighting plagues and predators to protect Australia's biodiversity

Our new report, Fighting Plagues and Predators, outlines the impact of invasive species on Australia's biodiversity https://www.csiro.au/en/news/All/Articles/2021/November/invasive-species-australia