Ecology Midterm

Natural History & the Scientific Method: Observation vs Hypothesis driven science

Observation is noticing something in nature. A hypothesis is a testable explanation of a phenomenon. Observation is the first of many core steps to the scientific method: 

1. Observe 

2. Question 

3. Hypothesis 

4. Predict 

5. Experiment 

6. Data Collection & Analyze 

7. Repetition & Iteration 

Natural History & the Scientific Method: Systems thinking: stocks, flows, feedbacks

Systems thinking is an approach that views parts of a system working together (interactions and relationships) through a holistic, rather than isolationist, lens.

“Interconnected elements that achieve a function.”

Stocks: are quantities of materials or information stored in a system, like biomass.

Flows: are the rates at which stocks increase or decrease (change in energy), like photosynthesis. Includes inputs and outputs.

Feedbacks: are responsive actions or information given to an influenced factor. They can be reinforcing or balancing. 

Key Characteristics of a System

CIBF

Components, Interactions, Boundaries and Function

Natural History & the Scientific Method: Emergent Properties vs. Predictable Properties

Emergent properties are a characteristic of a system that arise when individual parts of a system interact in a complex way, that cannot be predicted just from looking at the parts. For example, bird migration may have emergent properties. (Holistic)

Predictable properties are what we can infer from a system. They can be bottom-up or top-down. For example, if I know reproduction rates, I can model population growth. (Reductionist)

Energy

Energy is the ability to do work. For example, I have medium E.

Energy Flow in Ecosystems: Laws of thermodynamics

1. Energy can neither be created or destroyed 

2. Energy Transfers are inefficient (90% lost as heat)

   1. Only 10% to next trophic level

Energy Flow in Ecosystems: GPP, NPP, Trophic Efficiency 

GPP: Gross Primary Productivity: Total energy fixed by autotrophs

NPP: Net Primary Productivity: Energy left available to consumers after respiration 

1. NPP: GPP - R (respiration) 

Abiotic Factors

Non-living 

1. Sun

2. Rocks

3. Substrate

4. pH

5. Disturbance

6. Nutrients 

7. Water 

8. Gas

9. etc. 

Energy Flow in Ecosystems: Abiotic Influences on Energy Flow

Biotic + Abiotic components = Biosystems

Abiotic components have various influences on energy flow. For example, sunlight provides inputs to autotrophs and aids photosynthesis (growth). 

Water is basically required for all life. 

Soil is the medium from which stuff can grow. 

Disturbance resets succession. 

Evolution and Adaptation: Natural Selection and Fitness

Natural selection: is the core mechanism for evolution. It provides for variation, heritability, differences in survival and reproduction. Its mechanisms are gene flow, genetic drift, mutations, etc. 

Fitness: traits that influence survival

Mutation

Mutation is the change in DNA

Genetic Drift

Driven by chance, like the founder or bottleneck effect. It is a change in the frequency in existing alleles in a population. 

Gene flow

Gene movements among/between populations. Think of the different types of bears in GA caused by inbreeding. 

Consider: BIDE 

Evolution and Adaptation: Life History Strategies

How organisms allocate resources to growth, reproduction, and survival across their lifespan.

Encompasses Maturity, Fecundity (reproductive rates), Lifespan, and Investment 

R (many) vs K (few) selected 

Formula: dN/dt = rN(K-N) / K 

r = rate of increase 

K = carrying capacity 

N = population size 

Reproduction Types

Semelparity: Invest all resources into maximizing your single reproductive event. No need for parental care afterwards. Like salmon.

Iteroparity: Reproduce multiple times over a lifetime.

Evolution and Adaptation: Trait-environment relationships

Niche: Role of an organism in its environment. Understanding niches is important because it tells us about adaptation, distribution, and helps with managing ecosystems and biodiversity.

Adaptive radiation: is the rapid diversification from a common ancestor to exploit new ecological niches. Think of Darwin’s finches. 

Population Ecology I: Growth Models: Exponential vs logistical growth

Exponential Growth: under ideal env. conditions with unlimited resources there is high birth rate and a low death rate, but acceleration occurs only for short periods.

Logistical Growth: Under this model populations can only be supported up to a carrying capacity (K). This means they have limited resources and/or environmental constraints. 

Population Ecology I: Growth Models: Life tables, survivorship curves (Type I/II/III)

Life table: a record of survival and reproduction rates in a population. Divided by age, size, or developmental stage. They are used to asses patterns of mortality and growth rate.

Survivorship curve: Number of members of groups still alive at an age

Type 1: Humans (high rates of survival)

Type 2: Constant change of dying

Type 3: Early death rate but established maturity 

Population Ecology I: Growth Models: Calculating r, R₀, N(t)

Growth models measure the net reproductive rate (R0), average rate of reproduction (T), and total population growth rate. mx is age specific reproduction. 

Population Ecology II: Regulation & Limits: Density dependence, carrying capacity (K)

Carrying capacity (K): is the max pop. size an environment can sustain given its resources.

Density dependence: Density influences survival: Inverse to birth rates and direct with death rates.

Population Ecology II: Regulation & Limits: Allee effects, limiting factors, bottlenecks

Allee Effects: Phenonema where at low points of density cooperative populations experience low birth rates which puts them at risk for extinction. 

Limiting Factors: Inbreeding depression, less genetic diversity

Species Interactions: Mutualism, parasitism, competition, predation

Species Interactions: Food web structure, interaction matrix