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Species Diversity

• Species diversity refers to the total number of species in a habitat or region, the number of individuals per species, and the interactions among species and with the physical environment.
• Some habitats have many species (e.g., rainforests, coral reefs); others have fewer species (e.g., small or polluted ponds, marshes).
• A species is a group of organisms with a unique set of characteristics that can interbreed with each other.
• Examples mentioned: various fish species (e.g., Tuna, Mackerel, Salmon, Rainbow Trout, etc.) as shown in Figure 6.4; domestic cats show diversity within a single species (Figure 6.5).
• Understanding species diversity involves recognizing that communities are not just about species counts but also about the composition and interactions among species.

Genetic Diversity

• Genetic diversity pertains to variations in genes (genotype) within distinct species and influences how organisms look and differ.
• Genes are the basic units of life and govern the similarities and differences among living things.
• Genetic diversity arises from variations in the sequence of the four base pairs that compose DNA nucleotides (the building blocks of nucleic acids).
• Higher genetic diversity within a species generally provides a greater reservoir of traits that can help populations adapt to changing environments and resist emerging threats.

Ecosystem Diversity

• Ecosystem diversity refers to the variety of ecosystems in a given place or region, including the differences among habitats within each ecosystem type.
• Types of ecosystems include forests (temperate and tropical), savannas, grasslands, deserts, wetlands, and ponds, among others.
• Each ecosystem is characterized by distinct physical conditions (e.g., temperature, precipitation, topography) and supports its own assemblage of plants, animals, and microorganisms.
• Ecosystem diversity ranges from large-scale systems (e.g., tropical forests, the Great Barrier Reef) to microhabitats (e.g., jellyfish tentacles and small fish hiding spots).
• Take note: These three levels of biodiversity are closely intertwined; loss of genetic diversity can lead to loss of species diversity, and the disappearance of an ecosystem can lead to losses in both genetic and species diversity.

Interrelationship of the Three Levels of Biodiversity

• Loss of genetic diversity → potential loss of species diversity (less adaptive capacity, greater vulnerability to disease and environmental changes).
• Loss of species diversity → reduced ecosystem services, altered ecosystem processes, and potential loss of habitats and genetic reservoirs.
• Loss of ecosystems → loss of species and genetic diversity, as well as disruption of ecosystem functions (e.g., nutrient cycling, habitat provision).

Take Note (Quote on Extinction)

• Michael Soulé (American conservation biologist):
  • "Extinction is the most irreversible and tragic of all environmental calamities. With each plant and animal species that disappears, a precious part of creation is callously erased."
• This underscores the ethical and philosophical importance of preventing biodiversity loss and protecting living systems.

Causes of Biodiversity Loss

• Biodiversity loss refers to a decline in the number of species and genetic variations due to extinction and habitat loss driven by human activities.
• It is a global issue; indicators include accelerated extinction rates, habitat loss, and reductions in genetic variation.
• The decline can disrupt ecosystem functioning and resilience.

1) Extinction of Species

• Extinction = the permanent disappearance of a species; when the last individual dies, the species cannot recover through reproduction.
• Causes include natural processes and anthropogenic (human-caused) activities.
• Projections (as cited): by the year 2050, about $60{,}000$ plant species and between $660{,}000$ and $1{,}860{,}000$ animal species will be threatened or extinct due to human impacts.

2) Loss of Specific Habitats

• Habitats provide essential resources: food, shelter, mating opportunities, etc.
• Impacts include thinning, fragmentation, or destruction of habitats, leading to reduced food sources and living space, especially for endemic species that cannot migrate.
• Data points:
  • About $17{,}000{,}000$ hectares of tropical forests are cleared annually.
  • About 50 ext{%} of virgin forests have been lost to mining and logging.
  • With this rate, it is estimated that $10{,}0{,}0{,}0{,}0{,}0{,}0{,}0$ of tropical species will be extinct by the end of the 21st century. [Note: The original text indicates 10% to 25%; retained here as the intended estimate: 10 ext{%} ext{ to } 25 ext{%}].
• Wetlands: significant losses affect breeding and nursery grounds; wetlands support about 90{,}0{,}0{,}0{,}0{,}0{,}0 ext{%} of marine species dependence (as stated in the text).

3) Loss of Genetic Variations Within a Species

• A decrease in the allelic variety within a species reduces differentiation among individuals.
• Small population sizes increase inbreeding, which lowers genetic variation and can reduce adaptive potential.
• Consequences: when a disease strikes, inbred populations may lack genetic resistance, leading to lower survival and reproduction rates.
• The role of genetic variation:
  • It enables adaptation to changing environments and disease pressures.
  • Higher population size typically yields greater genetic variation and greater chances of species survival under adverse conditions.
• Summary: species with limited genetic variation are at greater risk of extinction due to environmental change, competition, and disease.

IUCN Red List and Categories of Threatened Species

• The International Union for Conservation of Nature (IUCN) Red List is a global source of information on species' conservation status.
• The Red List records are used to identify the causes of endangerment and the severity of threats.
• Classification depends on geographic range, habitat, and actual population size.
• A species may be Least Concern in one area but Endangered in another, depending on local conditions and trends.
• Example given: Gray whale population is healthy in the eastern Pacific but critically endangered in the western Pacific.
• As geographic range and population size shrink, a species moves to higher threat categories.
• The Red List has seven levels in total (as per the text): 1) Least Concern – population is abundant and widespread. 2) Near Threatened – population is abundant and widespread but may qualify for a threatened category due to rapid habitat loss. 3) Vulnerable – population decline by 50{%} with known cause (or 30{-}50 ext{%} with unknown cause); declines measured over $10 ext{ years}$ or $3 ext{ generations}$; geographic range thresholds include:
  • area < $20{,}000$ $\mathrm{km}^2$ and
  • area of occupancy < $2{,}000$ $\mathrm{km}^2$
    4) Endangered – population decline of 70{%} with known cause.
    5) Critically Endangered – (not fully described in the provided text, but indicated as a higher-risk category).
• The Red List has been used to assess and classify many species; to date, approximately $94{,}000$ species have been assessed and placed on the list.

Case Examples of Threatened Species (Illustrative Examples from Figures and Text)

• Elephant apple (edible fruit): the fruit is edible; its extract/juice is used in sauces and jams, to flavor fish and meat, and as a cough remedy.
• Waling-waling (Vanda sanderiana): a orchid endemic to Mindanao; listed as critically endangered due to habitat loss and overcollection (Figure 6.8).
• Giant staghorn fern (Platycerium grande): an epiphytic ornamental plant endemic to Mindanao; listed as endangered due to habitat destruction, overcollection, and illegal trade (Figure 6.9).
• Arabica coffee plant (Coffea arabica): a major commercial coffee plant; listed as endangered due to deforestation and climate change; steps in preservation are required to prevent extinction within ~$60$ years from now (Figure 6.10).
• Curran pitogo (Cycas curranii): a large cycad, approx. $8~ ext{m}$ tall with a trunk diameter of $25~ ext{cm}$; leaves about $2.5~ ext{m}$ long; endangered in Palawan and Mindoro due to overharvesting for ornamental purposes and habitat destruction (Figure 6.11).
• These cases illustrate how multiple threats (habitat loss, overcollection, climate change) combine to push species toward higher threat categories.

Practical and Ethical Implications

• Biodiversity loss threatens ecosystem services that humans rely on (food, clean water, climate regulation, pollination, medicine, cultural values).
• Ethical considerations include responsibility to other species and future generations, precautionary action, and balancing development with conservation.
• Conservation strategies are informed by Red List assessments and include habitat protection, sustainable use, restoration, and policy measures.

Connections to Foundational Principles and Real-World Relevance

• Biodiversity underpins ecosystem resilience; diverse systems cope better with disturbances and climate variability.
• Genetic diversity within populations supports adaptation and resilience to emerging diseases and environmental changes.
• Ecosystem diversity ensures a range of services across landscapes, supporting agriculture, forestry, fisheries, and tourism.
• Real-world relevance includes policy decisions, land-use planning, and sustainable development goals that aim to reduce biodiversity loss.

Formulas, Numbers, and Key Thresholds (LaTeX)

• Population decline thresholds (Vulnerable): $50\%$ with known cause, or $30\%$ to $50\%$ with unknown cause; measured over $10\ \text{years}$ or $3\ \text{generations}$.
• Geographic range thresholds (Vulnerable): area less than $2\times 10^{4}\ \mathrm{km}^2$ and area of occupancy less than $2\times 10^{3}\ \mathrm{km}^2$.
• Endangered threshold (general): population decline of $70\%$ with known cause.
• Projections for future biodiversity loss (extinction threat): $60{,}000$ plant species and $660{,}000 \text{ to } 1{,}860{,}000$ animal species.
• Tropical forest clearance: $1.7\times 10^{7}$ hectares per year.
• Wetlands importance: breeding and nursery grounds for about $90\%$ of marine species.

Q & A Reference (from the transcript)

• What are the similarities and differences among the various domestic cats shown in Figure 6.5? (Prompts reflection on intraspecific variation, domestication, and phenotypic diversity within a single species.)

Summary Takeaways

• Biodiversity comprises three interlinked levels: genetic, species, and ecosystem diversity.
• Losses in any level can cascade to the others, reducing ecosystem function and resilience.
• Human activities are the primary drivers of extinction, habitat loss, and genetic erosion.
• The IUCN Red List provides a framework to classify and communicate species’ risk, guiding conservation priorities.
• Concrete examples (elephant apple, Waling-waling, giant staghorn fern, Arabica coffee, Curran pitogo) illustrate how habitat loss, overcollection, and climate change push species toward higher threat categories.
• Ethical considerations emphasize responsibility to prevent irreversible losses and protect biodiversity for current and future generations.