Part 2: Understanding the interface between humans and animals

8 Issues in Biodiversity

Authors: Kao, K.

Learning Objectives

  • After reading this chapter you should be able to:
    • List the benefits of biodiversity to human health​
    • Explain how local and planetary biodiversity are sustained​
    • Describe how human activity contributes to loss of biodiversity​
    • Provide examples on how loss of biodiversity impacts negatively on human health

Keywords for loss of biodiversity:

  • Ecological niche​, habitat destruction, reproductive fitness, biodiversity, healthy environments

Loss of Biodiversity

What is biodiversity?

II. Loss of Biodiversity

In simplest terms, biodiversity refers to the variety of different living species that exist within a particular habitat. The concept can range from the bacterial flora in the gut to small ecosystems such as a treetop canopy, to large habitats such as an entire continent. Biodiversity also applies to the planet earth, defining all of the living organisms living in the atmosphere, the land, bodies of water and beneath the surface as well.

Regardless of the size of the habitat, it is important to know that each living individual exists in a relationship with all of the other individuals in its surroundings. How an individual interacts with its neighbours is in part deterministic, based on genetics inherited through the species, but only in a probabilistic manner, depending on many factors, both physical and biological. Likewise, each individual must play a role in the ecological niche that it inhabits – environmental changes can alter the niche, which can either benefit or be detrimental to the individual.

In a balanced ecosystem, multiple species compete or complement each other such that they are able to successfully reproduce. The conditions for successful reproduction can be intricate and highly demanding from an energy perspective. The challenge for a species to survive lies in the ability of its individuals to find or modify their environment and themselves in order to maximize their chances of reproducing successfully.  Thus, the term “Reproductive fitness” is a concept that means the ability of a species to pass down its genes to the next generation. Ensuring that all species have the opportunity to be reproductively fit is a requirement to maintain life on the planet.

What is biodiversity and Why is it important?

As noted by the NRC (1999), understanding the importance of biodiversity is essential to developing a plan to manage biodiversity and thereby mitigate the loss of biodiversity, regardless of the environment. A more recent statement on the management and planning approaches that will lead to a deceleration of the loss of biodiversity, is to consider the integration of biodiversity into several levels of our daily lives (Kuhl, Bowler, Bosch, et al 2020). What this requires however is a willingness to share information across data collection systems and to accept approaches such as using citizen science to collect information and disseminate information a the local level. Moreover, for healthcare, the loss of biodiversity means the complete removal of existing species that will be unavailable for future opportunities. Continuing unabated, the loss of biodiversity will have negative consequences not only for the species that are made extinct but also for the future existence of the human species.

(reference here: NRC 1999. Perspectives on biodiversity: valuing its role in an ever-changing world. Washington, DC: National Academy Press. 129 p.)

Key Takeaways

  • Biodiversity means the variety of different living species living within a habitat
    • Small ecosystem
    • Large habitat
    • Entire planet Earth
  • Species variety ranges from viruses and microorganisms to the largest plant and animal species
  • Species inhabit and evolve in niches/habitats to optimize their reproductive fitness
    • Interrelationships – niche
      • Commensal, parasitic
    • Reproductive fitness
      • Ability for a species to pass down their genes to the next generation
      • Required to maintaining balanced planetary ecosystem
    • Habitats range
      • Land masses
      • Oceans and freshwater bodies
      • atmosphere
In this section, there are 4 objectives:
  1. to list the benefits of biodiversity to human health – Every species on earth relies on other species for a balanced co-existence. As biological organisms, humans also inhabit a place on Earth that benefits from and contributes to biodiversity
  2. to explain how local and planetary biodiversity are sustained– The range of living organisms on the planet is sustained by ensuring their reproductive fitness. Both living and non-living features of the planet are essential to creating the conditions that optimize the ability for all species to pass down their genes to subsequent generations
  3. to describe the contribution of human activity to the loss of biodiversity – Since their existence on Earth, humans have exploited the resources of the planet in their favour to ensure an unfair advantage in reproductive fitness over that of other species. Humans shape the planet in ways that protect them from harmful physical elements but also modify themselves with medicines that protect against harmful biological elements, with little or no regard for collateral damage inflicted on other species.
  4. to provide examples of how the loss of biodiversity impacts negatively human health – As members of the planetary biosphere, humans benefit from their natural relationship with non-human species. The loss of those relationships can lead to consequences impacting health.

Reproductive fitness

Biodiversity, which reflects the vast range of living organisms on earth, has arisen through a process of natural selection so that only the fittest individuals get to pass down their genes to their offspring. The fitness of a species is defined by its traits – phenotypes that allow them to survive in a defined ecological niche. Individuals within and between species compete to acquire or maintain their habitat, within the niche. This competitive strategy is the basis for the continuation of life to exist as the environment changes. The greater the variability or diversity of phenotypes, the greater the chances for life to continue as the environment shifts.

In that regard, humans can be thought of as the ”winners”, hands down, because rather than evolving naturally to adapt to environmental changes, humans engineer the environment to remain evolutionarily static, or at least stable. But over-engineering the Earth has caused uncontrollable shifts in the physical environment that have jeopardized swaths of species –humans seemingly seek to destroy the biological environment that they depend on.

(essential reference:

“Reproductive fitness reflects the ability of individuals to pass on their genes to subsequent generations. Fitness traits, also referred to as life-history traits, include measures of fertility and mortality and are complex phenotypes that are direct targets of Darwinian selection.” Heritability of reproductive fitness traits in a human population. Gülüm Kosova, Mark Abney, Carole Ober, January 26, 2010, PNAS, 107 (suppl_1) 1772-1778.

Take a few minutes to enjoy this video by Sir David Attenborough on Biodiversity.

Benefits of biodiversity to human health

Biodiversity is required for the living, natural infrastructure, and the softscaping of living organisms that provide shelter, such coral reefs, forests, dune vegetation and soil. The natural infrastructure provides essentials for human life including clean water, shade, wind protection and retention of symbiotic microorganisms for vegetation required for consumption.

Humans create physical infrastructure for protection but which is still subject to deterioration and destruction by large changes in the physical environment including natural disasters. Living infrastructure is at a much larger scale than anything humans can produce and can adapt to a changing physical environment. On its own, the living infrastructure is much better suited to large changes in the physical environment. However human intervention has threatened to reduce biodiversity, and in so doing threaten their own existence.

The term Symbiosis is used to describe mutually beneficial relationships between species that allow them to thrive independently. The loss of biodiversity has taught us that symbiotic relationships are not only beneficial, but essential to good health. While we may perceive our bodies as a collection of billions of cells all with the same, or closely similar genetic identity, our bodies actually are living spaces for a greater number of microorganisms, several trillion, in fact. These microbes constitute the body’s microbiome, which is essential for a healthy life. The gut microbiome produces feces that become recycled into soil to support vegetation which provides food for consumption.

The body’s microbiome is perhaps a microcosm for the importance of planetary biodiversity. In fact the existence of a physiological microbiome clearly defines our bodies as part of, or integral to planetary biodiversity. An obvious benefit of biodiversity is of course food, including animal and plant protein, but in our quest to feed as many mouths as possible, too much of a good thing by over-development of agricultural spaces and over exploitation of animal species is a threat to biodiversity.

In our discussion of the importance of inter-species relationships, one of the areas for which biodiversity is important is in the role of certain species which serve as a reservoir for parasitic infections. These species serve as a Buffer zone of sorts, which provide a defense against interspecific transmission to humans, a concept known as zoonosis.

Biodiversity is not only important for physical health. Natural environments have always provided a respite for humans, as an aesthetic retreat for recreation and mental health.

Not all microorganisms are living symbiotically within us, with some parasitic, which can cause infection and for which we have immune systems and medicines to combat. On that note, most beneficial pharmaceuticals have been derived from natural sources. Aboriginal medicine and traditional healing methods, for example are perhaps the earliest form of healing therapy that were derived from natural sources. Chemical technology has refined and concentrated the beneficial elements and include drugs such as digoxin, from the foxglove and anticancer agents from, for example the periwinkle (vinblastine) and the yew tree (taxanes).

Key Takeaways

  • Natural infrastructure
    • Water, shade, wind protection, soil retention
  • Commensal and microorganisms for plant growth – food
  • Symbiosis – intestinal flora, agriculturally beneficial microbes
  • Food –source of animal protein
  • Buffer zone for zoonotic disease
  • Provide an aesthetic natural environment for recreation and mental health
  • Drugs and drug discovery
    • Aboriginal medicine and traditional healing methods from natural sources
    • Source of novel pharmaceuticals [digoxin (foxglove), anti-cancer agents such as vinblastine, taxol (Yew tree)]

Anticancer drugs derived from plants

Here is an example of how plants have been used to create some of the most important pharmaceuticals used to treat cancer. Drug companies are in constant search for novel therapies to treat human disease in this approach. (Trends in Cancer, June 2020, Vol. 6, No. 6 — Towards the Microbial
Production of PlantDerived Anticancer Drugs. Courdavault, O’Connor, Oudin, Besseau, Papon).

What aspects of human activity affect biodiversity?

Unlike the majority of species, humans, in their own way and through evolution of a unique nervous system, seek to create or drastically modify existing physical spaces for protection and optimal growth and development, to allow them to have a selective survival advantage over other species. A single human can easily modify its surroundings to displace or remove species that may immediately and in the long term reduce their chances of reproducing.

Multiply that effect by several billion and you can see why humans in general have become a significant threat to biodiversity. This process of niche destruction, the loss of species and the knock-on effect of loss of interspecies relationships serve only to “burn down the entire house” leading to our own extinction.

In recent decades, there has been an alarming rate of species loss. The threat to the reproductive fitness of entire ecosystems and entire classes of living organisms has resulted from predatory extinction through excessive hunting and harvesting. Domestication of single-favoured species has out-competed the existence of closely related species. As well, genetically isolated species may serve as reservoirs to increase vector-borne infection in wild species.

We need to accept that Humans have a shared responsibility with all of the species of the planet, as caretakers of the biosphere.

Alarming rate of species loss

•      Threat to reproductive fitness of entire ecosystems and entire classes of living organisms

•      Predatory extinction

•      Hunting

•      harvesting

•      Domestication

•      Genetically isolated species may serve as reservoirs to increase vector borne infection in wild species – fish farming

•      Habitat destruction

•      Loss of niches leading to extinction or incursion into other habitats including human living spaces

•      Niche destruction  – species no longer able to interact

•      Climate change

•      Need to accept that Humans have a shared responsibility as caretakers of the biosphere

Humans (and indirectly all species) are stewards of the environment

Human activity that disregards the health of other living organisms affects human health

  • Altering physical habitats can threaten reproductive fitness of species living in those natural spaces
  • human populations have grown disproportionately
  • consume disproportionate amounts energy and produce a disproportionate amount of waste
  • There is a need to engineer human spaces that minimize impact on other species

There are 5 ways that humans have threatened biodiversity. In order to make our environment suitable to enjoy a long life, we have shaped the planet to our liking, causing loss of habitat of significant numbers of species.

To generate a lifestyle to satisfy a hunger for power and self-image, we have created chemical and petroleum-based products that pollute our air and water and have led to climate change, affecting species migration patterns by elimination of existing habitats.

The explosion of human populations worldwide has resulted in more mouths to feed, causing the exploitation of habitats for agriculture and the harvesting of natural species. In addition, the global movement of large masses of produce, products and people has resulted in the formation of new species relationships, some newly parasitic ones that result in the elimination of indigenous ones, thereby upsetting pre-existing extended relationships, many of which can be intricately complex

 Examples of how the loss of biodiversity affects human and animal health

 “Fish Farms a Viral Hotspot for Infection of B.C.’s Wild Salmon, New Study Finds”

Here is a good example of how human activity has directly impacted on biodiversity and subsequent negative consequences to human health and well-being. The thriving salmon farming industry in Canada is a lucrative industry with $1.6 billion in 2019 in British Columbia alone. Evidence has demonstrated that there is a high risk of viral and other parasitic infection in physically isolated fish populations raised using the preferable, open ocean-based farming methods. These infections are lethal and can spread to wild fish populations upon which First Nations communities rely.




•       Effect on First Nations Health (

Another example of how loss of biodiversity affects human health is in the ability for some non-passerine species to act as a vectorial “buffer” for West Nile virus infections. These birds include ducks, geese and other waterfowl, which act as less competent hosts as compared to passerines and have been linked to lower rates of infection in Humans. Loss of wetland habitats may lead to reduction in non-passerine birds.
Ezenwa VO, Godsey MS, King RJ, Guptill SC (2006) Avian diversity and West Nile virus: testing associations betweenvbiodiversity and infectious disease risk. Proceedings of the Royal Society Biological Sciences 273:109–117.

Pongsiri, MJ and Roman, J (2007). Examining the Links between Biodiversity and Human Health:An Interdisciplinary Research Initiative at the U.S. Environmental Protection Agency, EcoHealth 4, 82–85.

Another modeling study showed that biodiversity loss would lead to increased tick infections in humans.
(LoGiudice K, Ostfeld RS, Schmidt KA, Keesing F. The ecology of infectious disease: effects of host diversity and community composition on Lyme disease risk. 
Proc Natl Acad Sci U S A. 2003;100(2):567-571. doi:10.1073/pnas.0233733100)


Finally, here is a very clear demonstration of how deforestation and human settlement displaces species and increases malarial and other parasitic infection risk.

“Deforestation and the incidence of malaria.

Schematic diagram showing how the risk or incidence of malaria first increases and then decreases as deforestation proceeds. Before deforestation (bottom left) the forest is largely pristine, with a low population density and activities that do not cause deforestation. Malaria can be epidemic (1) and mostly driven by environmental/climatic conditions. As deforestation proceeds (bottom middle), humans start to colonize the area, roads (shown in grey) are built, and agricultural (yellow) and urban areas (white) follow. Malaria risk is enhanced (2) at this modified boundary between human settlements and the forest. Once deforestation is widespread, and after some time that depends on the region and alteration of the landscape (bottom right), the area can sustain only low but endemic malaria transmission (3); however, the risk of infection increases for other diseases transmitted by mosquitoes that thrive in this domesticated environment, such as dengue and Zika.


MacDonald J, and Mordecai, EA (2019) Amazon deforestation drives malaria transmission, and malaria burden reduces forest clearing 22212–22218 | PNAS | October 29, 2019 | vol. 116 | no. 44 “

We are the champions?

I want to end by circling back to our conceptual understanding of the role of biodiversity and how its precipitous loss is a detriment to planetary health.The late Stephen Jay Gould was one of the most prominent evolutionary biologists of our time. As The Agassiz Professor of Zoology at Harvard University, he was a prolific writer of books on the origin and evolution of life, questioning many of the traditional views of our place on Earth. Gould challenged the anthropocentric view of humans at the top of biological complexity in which the human body represents the epitome of life’s success on Earth.

The basis for his argument is that the largest biomass from the origin of life until now, belongs to the unicellular prokaryotic organisms, the bacteria and blue-green algae. Vertebrates, and in particular humans, are relatively late developments; but their existence depends on the vast diversity of preceeding life organisms. In fact, one could go so far as to say that humans evolved as habitats for the microbiome that inhabits the digestive systems of every person. In todays context, Gould’s book, “Full House”, published in 1996, could not have greater significance and impact to planetary and human health.

In the concluding chapter entitled “The power of the modal Bacter, or why the tail can’t wag the dog” he puts forward his main argument that symbiosis with our single-celled “masters” found in soil, in the air and in the water, is essential for existence of all life on the planet. They form the largest proportion of biomass, which supports all of the more complex organisms including humans These microbes are necessary to recycle the basic nutrients required for all life; altering the physical world jeopardizes planetary biodiversity and extinction of species, including ultimately our own.

Gould’s prophetic work provides the scientific basis for the reasons why biodiversity is essential for the continuation of life on Earth. Humans and complex species are simply the twigs of a massive foundation consisting of a massive trunk of microorganisms and single celled beings – ignoring them and their relationship to our well-being in the process of an ever changing physical planet threatens our very existence as a species.


Principles of Planetary Health Copyright © 2022 by the authors. All Rights Reserved.

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