Animal Diversity and Characteristics

General Features of Animals

Animals are multicellular, heterotrophic organisms that originated from a common ancestor. They exhibit coordination, specialization, and communication among different cell types, which arise due to gene expression. These features allow animals to access more food and adapt to various environments.

• Multicellularity: Animals are composed of multiple cells with specialized functions.

• Monophyletic Origin: All animals share a common ancestor, making them a monophyletic group.

• Movement: Most animals can move under their own power, a trait used to define the group.

• Ingestion: Animals are true consumers, ingesting and digesting food internally.

• Sessility: Some animals, such as certain marine species, can be sessile for periods of their lives.

Additional info: The ingestion process in animals is called phagocytosis in some unicellular forms, but most multicellular animals use specialized digestive systems.

Unique Animal Traits

Some traits are present only in certain animal lineages:

• Tissues: Most animals (except sponges) have specialized tissues, such as muscle and nervous tissue.

• Bilateral Symmetry: Bilaterally symmetrical animals exhibit centralization, with a head region (cephalization) containing mouth organs and a brain.

• Vertebral Column: Vertebrates possess a central supporting structure (spine).

Biodiversity: Concepts and Measurement

Definition and Importance

Biodiversity refers to the variety and variability of life on Earth. It can be characterized in many ways, including species richness, evenness, and phylogenetic diversity.

Measures of Biodiversity

• Species Richness: The number of different species in a given area. Also called alpha diversity.

• Species Evenness: Measures the relative abundance of different species in an area.

• Gamma Diversity: The total number of species across multiple habitats.

• Eta Diversity: Quantifies the difference in species composition between habitats.

• Phylogenetic Diversity: Measures how much evolutionary history is represented in a community (sum length of branches on a phylogenetic tree).

• Functional Diversity: Assesses the variety of ecological roles, traits, and functions of organisms in a community.

Comparison Table: Biodiversity Measures

Major Events in Biological History

Timeline of Key Events

• Life on Earth: ~3.5 billion years ago (bya)

• Eukaryotes: Later evolved

• First multicellular organisms: 1.6–1 billion years ago

• Land plants: 450–500 million years ago (mya)

• Land vertebrates: 375 mya

• Dinosaurs: 350–65 mya

• Mammals: 260 mya

• Flowering plants: 50 mya

Ecological Opportunity and Adaptive Radiation

Ecological Opportunity

Ecological opportunity arises when a new or available ecological niche allows species to occupy, adapt, and diversify. This can occur due to new resources, invasion of new habitats, evolution of innovations, or loss of competitors.

• Example: Flowering plants evolved, providing new food resources for animals.

• Coevolutionary loops: Many evolutionary pathways lead to reproductive isolation and speciation.

Adaptive Radiation

Adaptive radiation is the rapid diversification of a single lineage into many species, each adapted to exploit different resources or habitats.

• Occurs when a lineage gains access to open ecological opportunities.

• Results in high average fitness and diversity.

Extinction and Conservation Biology

Mass Extinctions

Mass extinctions are events where many species go extinct in a short time, often due to rapid environmental changes. These events reset ecosystems and open ecological niches for surviving species to diversify and adapt.

• Current extinction rates are much higher than normal background rates.

• Human activities are a major cause of recent extinctions.

Human Impacts on Biodiversity

• Habitat loss and fragmentation

• Introduction of invasive species

• Climate change

• Overexploitation

Fragmentation breaks habitats into smaller pieces, reducing movement and genetic diversity, and increasing vulnerability to extinction.

Population Dynamics and Vulnerability

• Small populations are more vulnerable to random events, genetic defects, and inbreeding depression.

• Inbreeding increases homozygosity, leading to reduced fitness.

• "Extinction vortex" describes the cycle of vulnerability and decline in small populations.

Niche Concepts

• Fundamental Niche: The full set of conditions and resources a species could use.

• Realized Niche: The actual conditions and resources a species occupies due to competition and environmental constraints.

Conservation Strategies

• Captive breeding and strategic release to maximize genetic variation and minimize inbreeding.

• Habitat restoration and management to improve quality and connectivity.

• Re-establishing species through captive breeding and recovery programs.

Conservation works: Protecting areas, sustainable resource management, and restoring connectivity can help reverse population declines.

Key Terms and Definitions

• Monophyletic: Originating from a single common ancestor.

• Alpha Diversity: Species richness in a specific area.

• Gamma Diversity: Total species across multiple habitats.

• Phylogenetic Diversity: Evolutionary history represented in a community.

• Adaptive Radiation: Rapid diversification of a lineage into many species.

• Extinction Vortex: Cycle of decline in small populations due to genetic and ecological factors.

• Inbreeding Depression: Reduced fitness due to increased homozygosity.

Formulas and Equations

• Relative Abundance (Evenness):

• Species Richness (Alpha Diversity):

• Gamma Diversity:

Summary Table: Human Impacts and Conservation

Additional info: Conservation biology integrates genetics, ecology, and management to sustain biodiversity and ecosystem function.