Ch04_outline - Tagged (1)

Chapter 4: Life: What Shapes Biodiversity?

Introduction

• Biodiversity: Refers to the variety of life on Earth, with over 2 million species of animals identified and many more yet to be discovered, including estimates suggesting a total of 5 to 30 million species exist when considering all forms of life.

• Human Impact: Humans significantly decrease overall biodiversity through habitat destruction, pollution, climate change, and overexploitation of resources, threatening many species’ survival and altering ecosystems.

• Sustainability: Emphasizes the importance of supporting Earth’s biodiversity through methods that do not compromise future generations’ ability to meet their needs, promoting balance within ecosystems.

4.1 What Do Living Things Have in Common?

• Characteristics of Living Things:

  • Homeostasis: Organisms maintain stable internal conditions despite external environmental changes.

  • Metabolism: All living organisms convert food into energy and build biological structures.

  • Reproduction: Living beings have the ability to reproduce, ensuring the continuation of their species, either sexually or asexually.

  • Adaptation: Organisms adapt to their environments over time, enhancing their chances of survival.

• Study Scales:

  • Population: Consists of individuals of the same species sharing a habitat; includes genetic variation, health, and responses to environmental pressures.

  • Community: Comprises various species living in a certain habitat, interacting in complex relationships of competition, predation, and symbiosis.

  • Ecosystem: Encompasses all living organisms and their physical environments in a given area, studying the flow of energy (through food chains) and matter (nutrient cycles).

  • Biome: Large geographical areas characterized by distinct climate and ecosystems, such as forests, grasslands, deserts, and tundras.

  • Biosphere: The global sum of all ecosystems; it is the zone of life on Earth, integrating land, water, and the atmosphere.

• Evolution: The genetic changes in populations over generations, demonstrating adaptations and the complexity of life through geologic time.

4.2 How Does Life Evolve?

• Charles Darwin:

  • Conducted important observations of various organisms and habitats during the HMS Beagle voyage (1832), forming the basis of theories about natural selection.

  • His studies on the adaptive traits seen in organisms, like the variations in Galapagos finch beaks, highlighted the importance of adaptation to environment.

• Natural Selection:

  • Organisms with traits that better suit their environments are more likely to survive, reproduce, and pass those traits to the next generation.

• Adaptive Radiation:

  • Occurs when an ancestral species diversifies into several new forms, adapting to different environments or niches, enhancing the biodiversity observed.

• Genetics and Evolution:

  • Genes: Fundamental units of heredity made of DNA; they play a crucial role in determining traits in organisms.

  • Alleles: Variants of genes; different alleles can lead to variations in traits among individuals.

  • Phenotype vs. Genotype: Phenotype includes all observable characteristics, while genotype refers to the specific genetic makeup of an individual.

• Mutations:

  • Spontaneous genetic changes that can introduce new traits into a population; mutations can be categorized as beneficial, harmful, or neutral.

  • Positive Selection: Favorable mutations that enhance survival and adaptation become more common over time.

  • Negative Selection: Detrimental mutations may decrease in frequency as they affect survival negatively.

• Extinction:

  • Represents the permanent loss of a species, often due to inability to adapt to changing environments or catastrophic events; mass extinction events have occurred multiple times throughout Earth’s history.

• Misconceptions about Evolution:

  • It is important to recognize that evolution does not indicate progress; it is a process of change driven by environmental pressures and survival needs. Evolutionary changes happen at the population level, not individual levels. Adaptation is often a response to environmental challenges, not an intentional effort by organisms.

4.3 What Causes Population Traits to Change?

• Speciation:

  • The process by which new species arise from existing species due to genetic divergence over time, often driven by reproductive isolation.

  • Allopatric Speciation: Occurs when populations are geographically separated, leading to evolutionary paths that do not allow interbreeding.

• Genetic Diversity:

  • High genetic diversity within populations increases their resilience to diseases and environmental changes, thereby enhancing ecosystem productivity and stability.

  • Influences include gene flow (the transfer of genetic material between populations), inbreeding, outbreeding, and genetic drift (random changes in allele frequencies).

4.4 What Shapes Biodiversity?

• Environmental Factors: Conditions like climate, geography, and available resources profoundly shape the composition and richness of biological communities in particular areas.

• Species Richness:

  • Indicates the number of different species found in a particular area; currently estimated that 2 to 15 million species exist, with ongoing research continually refining these estimates.

  • Current data shows that while many vertebrate species are well-described, numerous invertebrate species remain poorly studied.

• Species Evenness:

  • Refers to the relative abundance among species in a community; communities dominated by a few species may be less stable than those with more even distributions of species.

• Ecosystem Diversity and Biogeography:

  • Latitudinal Gradient: Tropical regions usually contain more species due to optimal climate conditions, more resources, and stable environments.

  • Biomes: Diverse ecological units characterized by specific climates, vegetation, and organisms, often leading to convergent adaptations among unrelated species exposed to similar environmental pressures.

4.5 How Do Communities of Organisms Interact?

• Competition:

  • A fundamental force in natural selection where individuals vie for limited resources, affecting population dynamics and species distribution.

  • Types of Competition:

    • Intraspecific: Competition among members of the same species.

    • Interspecific: Competition between individuals of different species, which can lead to resource partitioning and niche differentiation.

• Predation:

  • The interaction wherein one organism (the predator) feeds on another (the prey), influencing population sizes and community structure.

  • Herbivory: Specific interaction affecting plant populations through grazing.

• Coevolution:

  • The process by which two or more species evolve in response to each other; can result in mutual adaptations, leading to an evolutionary arms race.

• Symbiotic Interactions:

  • Long-term relationships between species that can be classified into three main types:

    • Parasitism: One organism benefits at the expense of another.

    • Commensalism: One species benefits while the other is neither helped nor harmed.

    • Mutualism: Both species benefit from the interaction.

4.6 What Controls Population Size?

• Population Dynamics:

  • Changes in a population’s size and structure are influenced by reproduction, immigration, emigration, and mortality rates.

• Growth Patterns:

  • Exponential Growth: Occurs when resources are abundant, resulting in rapid increase.

  • Carrying Capacity: The maximum population size an environment can sustain, where populations may crash if resources are depleted.

  • Logistic Growth: Population growth that fluctuates around the carrying capacity due to resource limitations.

• Density Factors:

  • Density-dependent factors include competition, predation, and disease, all of which impact population growth more strongly as population size increases.

  • Density-independent factors, such as natural disasters, affect population size regardless of its density.

• Reproductive Strategies:

  • r-strategists: Species that reproduce rapidly with little parental investment, often in unpredictable environments.

  • K-strategists: Species that reproduce at a slower rate but provide significant care for their offspring, typically found in stable environments.

4.7 What Can Cause Loss of Biodiversity?

• Extinction as a Natural Event:

  • Extinction can occur gradually or through rapid events; understanding background rates and contributing factors is essential for conservation.

• Biodiversity Hot Spots:

  • Geographic areas boasting exceptional levels of endemic species but also facing serious habitat loss and degradation; these regions are prioritized for conservation efforts.

• Keystone Species:

  • Organisms that have an outsized impact on their ecosystems; their removal can lead to significant changes in community structure and loss of biodiversity.

4.8 What Can I Do?

• Create Wildlife Habitats:

  • Encourage the presence of wildlife in small spaces such as yards or balconies, promoting native plant growth and reducing lawn areas that are non-supportive to local species.

• Reduce Negative Impacts:

  • Adopt sustainable consumption practices, limit waste production, and strive to mitigate pollutants, including noise and light pollution that adversely affect wildlife.

• Minimize Impact When Outdoors:

  • Follow the "leave no trace" principles, ensuring minimal disturbance to the natural environment during outdoor activities, which helps preserve biodiversity and ecosystems.