Lecture 13 BIO120

What is ecology and why does it matter?

  • Defining term “ecology” 

  • How many species are there?

  • Examples of species w large versus small geographic ranges

  • Examples of abundant and rare species

  • A framework for thinking about and determining species’ range and abundance

Ecology is NOT

  • Environmentalism

  • Not about recycling, reducing pollution and energy use 

Ecology is the science of: 

  • How organisms interact w each other and their environment

→ The word ‘ecology’ comes from the greek word oikos (home/place to live)

  • The distribution and abundance of species

  • The structure and function of ecosystems 

  • In a nutshell, the science of biodiversity 

Why teach ecology in intro to bio? → Theodosius Dobzhansky → “nothing in biology makes sense except in the light of evolution” 

  • True, but nothing in evolution makes sense except in the light of ecology! 

“The ecological theatre and the evolutionary play” 

  • title of a book by hutchinson (1965) 

  • Ecology is the setting where evolution plays out

  • Interactions between organisms and their environment give rise to natural selection

“Why?” versus “How?” questions

  • CSB tends to ask “How” questions: 

→ How do mitochondria work?

→ How do cells respire (i.e., make energy from food)?

→ What proteins do mitochondrial genomes encode?

  • EEB tends to ask “Why” questions: 

→ Why do eukaryotic cells have mitochondria? (why don’t prokaryotic cells have mitochondria?)

→ Why do mitochondria have their own genomes?

  • Both critically important, and complementary 

Endosymbiotic theory for the origin of mitochondria (Lynn Margulis) 

“Life did not take over the globe by combat, but by networking”

Ants take over amazon by networking (with plants) 

How many species are there?

  • Globally: 

→ Too many to count

→ Many (>85%) still unknown to science

→ One estimate, extrapolated from rates at which new taxa are described: 8.7 million (give or take about a million) (just eukaryotes…)

  • Biodiversity is not equally distributed across the tree of life → 70-90% of all species are bacteria

Model (fruit flies, mice, arabidopsis thaliana) vs. non-model organisms vs. basically all other living things 

  • A population is all the individuals of the same species in one place at one time (all the zebras in a savanna) 

  • An ecological community is all the species living together in one place at one time (all the zebras, giraffes, elephants, plants, insects, etc., in a savanna) 

  • An ecosystem is all the species plus the non-living environment (the entire savanna) 

Some species live almost everywhere: (mountain lions, red foxes, american pika)

Why care abt species ranges? 

  • Understand where plants and animals can grow because they give us food, clothing, wood, medicine, etc. 

  • Predict what will happen to biodiversity as the climate changes, a major goal of modern ecology

  • Predict how biodiversity will respond to habitat destruction, pollution, invasive species, etc. 

  • Microbes also have ranges we want to understand to determine disease risk

  • Basic science question of why nature is the way it is

Infectious disease agents are also species with patterns of distribution we want to understand

What determines where species live?

Dispersal → Abiotic conditions (climate, nutrients) → Species interactions (competition, predation, mutualism) → species in a community

What limits a species’ range? 

  • Dispersal

  • Climatic or other inexhaustible conditions, e.g., temp., salinity, etc. 

  • Food or other exhaustible resources, e.g., nutrients, space, etc.

  • Species interactions, e.g., competition, predation, or mutualism

  • These factors vary across space and time; we envision gradients of conditions

  • Organisms perform best at certain portions of a gradient

Some species are abundant (racoons) some rare (lonesome george, pinto tortoise in galapagos islands) 

What determines abundance?

  • Malthus → argued that size of a population cannot grow faster than the resources that support it 

The sixth extinction: 

  • Ongoing mass extinction, mainly as a result of human activities

  • 32% of known vertebrate species (8,851 out of 27,600 species) are decreasing in population size or range (Ceballos et al. 2015, PNAS)

  • North american birds have declined in abundance by 29% since 1970 (rosenberg et al. 2019, science)