biob50 Flashcards
What is ecology
Interactions among organisms and the environment and why these are happening and how these are happening
By okologie we mean the comprehensive science of the relationships of the organism to its surrounding environment, in which we include, in the broader sense, all “conditions of existence”
Ecology is the scientific study of the interactions of organisms with their environment and one another that determine their distribution and abundance
Everything in nature is interconnected
In general, organisms within ecosystems are connected in myriads of ways (e.g., through their resource needs), leading to complex interaction webs
The “great acceleration”
In the anthropocene, human impact has now grown to the point that it has changed the course of Earth’s history for millennia. Human actions dominate the planet and have led to a biological world that is rapidly shifting toward an unknown future state
Levels of biological organization
Individual
Population (group of individuals of same species, living and interacting with one another in a particular area)
Community (an association of interacting populations of different species, living and interacting in the same area)
Ecosystem: (a community of organism plus their abiotic (physical) environment)
Biosphere (all the world ecosystem)
Observation & natural history
Natural history is the study of animals, plants, and fungi, particularly focusing on observation and description (rather than experiment or scientific analysis)
Natural history is the historical foundation of the field of ecology but differs from modern approaches, where observations are typically combined with other approaches of scientific analysis
Experimental ecology & null hypothesis testing
From the second half of the 20th century onwards, ecologists increasingly began to apply manipulative experiments and statistical hypothesis testing
(i.e., researchers develop hypothesis about the mechanisms that lead to observed ecological patterns, and then conduct carefully designed experiments to produce evidence for supporting or rejecting the hypothesis)
Multiple hypothesis testing with best-fit comparisons
In many situations, experiments cannot be repeated (e.g., due to ecosystem idiosyncrasies over time and space), or conducted logistically (e.g., experimental approaches are typically biased towards small species and short timescales), or ethically (e.g., experimentally testing the effects of an increasingly stressful climate on an endangered species)
- however, large amounts of various types of data are often available or can be can collected by observation only, without manipulation. Similar to real-life sleuths, ecological detectives can use these data to assess the strength of evidence for a suite of hypotheses regarding which ecological processes might operate
Ecological modeling
Models play a fundamental role in modern ecology
Similar to experiments they allow exploring how various factors affect ecological dynamics, but without the need for experimental manipulation
Models can be used in many ways including for:
Understanding the mechanisms that lead to ecological patterns
Testing complex hypotheses against data
Estimating missing information (e.g., population numbers)
Identifying what we don’t understand about a system
Gilding management
Providing forecasts
A conceptual model for the global climate
Weather: current state of the atmosphere at any given time
Climate: long-term description of weather, including average conditions and the full range of variation
Climate change: directional change in climate over a period of at least three decades
Solar radiation: trends across latitudes
- higher latitudes receive slanting rays and more diffuse energy
- at lower latitudes the sun’s rays are more concentrated
Solar radiation: effects of the tilt of earth’s axis
Trends across latitudes are accentuated by the tilt of earth’s axis
This tilt, in combination with earth’s journey around the sun, results in regular, seasonal variations in solar radiation across latitudes
Atmospheric circulation
The Hadley circulation cell starts as warm, moist air rises at the equator due to solar radiation. As this air ascends, it expands and cools, releasing its moisture as rainfall. This dynamic produces tropical rainforests near the equator. Cold air is denser and drops back toward the earth. As it descends, it warms. The warm, dry air can absorb water from the earth’s surface, producing deserts at around 30 north and south latitudes.
polar, ferrel and hadley cell
Atmospheric low pressures result from descending columns of air. A rising column of air cannot rise without limit, so it also moves north or south, away from the equator. This movement toward higher latitudes, combined with the rise and fall of warmed and cooled air, creates interconnected cells of circulating air between the equator and the poles. This circulation pattern produces alternating high-and-low-pressure zones, as well as alternating bands of relatively wet and dry habitats at fairly predictable latitudes across the earth’s surface
The Coriolis effect
The Coriolis effect is caused by the earth’s spins and adds an easterly or westerly aspect to surface winds. Winds moving from higher latitudes to lower latitudes move eastward more slowly than the ground beneath them moves, which means they move westward relative to the ground. Winds that move away from the equator come from a part of the earth with a large circumference, so they spin east faster than the ground beneath them and are perceived by us as moving east. The northward or southward direction of the winds comes from the Hadley, ferre, and polar cells. The winds between 30 and 60 latitudes are westerlies, and the others are all easterlies.
ocean water
The spinning of the earth leads to circular patterns of movement in the worlds ocean waters. The circulation is generally clockwise in the northern hemisphere and counterclockwise in the southern hemisphere
Through earth’s rotation, the Coriolis effect affects wind patterns and oceanic circulation, with resulting effects on temperature and precipitation
Rain shadows
Topography influences the local climate, for example, via rain shadows
As warm, moist air is forced to a higher elevation over a mountain, it expands, cools, and loses its water as rain. On the back side of the mountain, air that has become cold and dry descends, warms, and absorbs water from the land surface, producing dry conditions
Heat capacity & continental effects
Differing heat capacity (how much energy needs to be added to a substance to raise its temperature by 1 degree Celsius) between water and soil (water has a five times higher heat capacity) leads to continental effects. The interior of continents experiences large season temperature swings, which in coastal areas, the ocean buffers the temperature changes, creating a moderating effect on the climate with cooler summers and warmer winters
Transpiration
plant life also influences the climate
The Amazon has a distinct rainy season that starts 2-3 months before season winds start to bring in moist air from the ocean
Plants cool the environment directly via transpiration (when plant tissue heats up, they release excess water vapor from pores in their leaves called stomata). This cools the plant in a similar way as sweating cools mammals
Biomes
Every species has its niche
Terrestrial biomes
Biomes = large geographic areas affected by similar climatic and physical factors, leading to distinctive formations of animals and plants
Terrestrial biomes are generally determined by climate (sunlight, temperature, water) and soil types, but theyre usually charcterized by characteristics of the plant community [e.g. plant growth form (trees, shrubs, grasses0, morphology (tall, short, shrubby), leaf characteristics (broadleaf, needle leaf), plant spacing (dense forest, open woodland, savanna)]
The definition of biomes focuses primary productivity (the synthesis of organic material by plants through photosynthesis) because this has a direct effect on the organismal composition of the biome. The diversity of plant species in an ecosystem tends to correlate with the diversity of other taxa.
The influence of temperature and precipitation
Each biome is characterized by a typical climate
Climate diagrams can be used to visualize how temperature and precipitation interact to determine plant growth, and how these factors vary across biomes
If blue sits above orange, more precipitation, less evaportion
Tropical rainforest
Always more precipitation compared to evaporation
Hot air rises, lots of precipitation
Tall trees, dense understory, and lots of species growing on other species
Hige diversity and abundance of animals
Tropical dry forest
Still hot
Precipitation starts becoming seasonal
In wet season, it becomes an emerald tangle of life, rivaling that of tropical rainforest; in the dry season though the majority of trees drop their leaves, and the landscape can appear brown and parched
Tropical savanna
Dry
Large open grasslands
Periods of rain arrive with large thunderstorms and frequent lighting strikes which can lead to recurrent and extensive fires
Desert
Just hot and dry air
Sun is sucking up all water
Animals are adapted
Evaporation excess precipitation
Mediterranean scrubland
High-pressure zone
Rain during winter when high pressure is not as strong (ocean is warm)
Wet winters and hot dry summers
Temperate grassland (prairies)
Cold frozen winter and a hot summer
Thunderstorms associated with rainfall in the summer produce lightning strikes causing frequent fires
The presence of periodic fires acts to produce and maintain the grassland, as the fire eliminates all but a few trees
Temperate forest
Deciduous trees (leaves fall off)
Summers are warm and humid, winters are often below freezing with snow
Dense canopy of dominant trees intercepts a large majority of the incoming sunlight, below is a secondary canopy of shorter trees, followed by a distinct shrub layer and a ground layer
Boreal forest (taiga)
Lots of precipitation
Cold
Winters are quite long and below-freezing temperatures can extend for 6 or more months
Tundra
Short growing season
Wet and soggy as a layer of permafrost underlies the entire region
Biological zones on mountains
On mountains, temperature and precipitation change in elevation, resulting in similar biological zones along elevation gradients as found across terrestrial biomes when moving poleward
Biomes are shifting upwards due to hot weather
Moving 1000 m up in elevation typically decreases the temperature by 6.4 degrees ~ the equivalent of moving 1400 km poleward
Aquatic biological zones
Unlike in terrestrial environments, we cannot use precipitation or soil type to define biological zones.
Instead, aquatic biological zones are determined by: light & nutrient availability, temperature, structure of the benthic (bottom) surface, salinity, physical movement of the water
Marine zones
Marine zones are characterized based on:
Light penetration: photic zone extends to 100-300 m depth; below the photic zone, energy and nutrients are supplied by falling detritus
Proximity to the shoreline
Physical location: benthic(bottom surface) or pelagic(in the water column)
Depth of the pelagic zone
Freshwater
Although freshwater systems share some characteristics and terminology with marine systems, their limited extent and network-like spatial structure lead to fundamental differences. Freshwater biomes are rarely defined; instead, freshwater systems can be characterized as lotic (flowing rivers and streams), lentic (stationary ponds and lakes), aquifer (subsurface water)
Climate change: historical patterns
The earth’s climate has changed several times through its history due to changes in earth’s tilt, its position relative to the sun, plate tectonics, volcanic activity, and meteor impacts
Anthropogenic climate change
Today, the climate is changing at unprecedented rates due to greenhouse gas emissions by humans
Greenhouse effect: warming of earth of atmospheric absorption and re-radiation of infrared radiation emitted by earth’s surface. The effect is due to greenhouse gases in the atmosphere, primarily water vapor (h20), carbon dioxide (co2), methane (ch4), and nitrous oxide (n2o)
Limiting factor
A limiting factor is a resource or environmental condition that limits the growth, distribution, or abundance of an organism or population within an ecosystem
The niche
A species’ tolerance to its limiting factors defines its niche, which can broadly be understood as the set of environmental conditions in which an organism can live and reproduce
Formally, a (Hutchinsonian) niche is defined as an n-dimensional hypervolume, where n indicates the number of different environmental conditions that determine where an organism can survive and reproduce
The niche: performance curves
An organism’s performance. Often quantified as the rate of a given physiological process (e.g., rates of movement, reproduction, mortality) varies along the axes of its niche space. It is low near the extremes of a limiting factor and optimal at some intermediate value. Performance curves describe this variation
Measuring the niche
Variations in the preferences of a species along one or more axes of their niche space can be measured by studying their behavior
Variation in physioloigcal performance due variations in limiting factors can often be measured experimentally (e.g., rearing individuals in thermal incubators for studying temperature effects)
Fundamental niche vs realized niche
In nature, the realized niche of a species (the set of environmental conditions where the species occurs) is typically smaller than its fundamental niche (the set of environmental conditions that a species could tolerate), as species are typically excluded from the extremes of their niche by better adapted, superior competitors and other factors)
Example: the barnacle semibalanus balanoides only occurs in the northern part of its potential range; it is excluded from the southern part by other barnacle species that are superior competitors
Energy, the currency of life
All metabolic processes require energy, including for the maintenance of cells the production of enzymes, growth, movement, reproduction & thermoregulation. Without energy, enzymes fail, cell membranes degrade, organelles cease to operate. Life is impossible
Heterotrophs obtain energy by consuming organic compounds from other organisms
Autotrophs convert the energy of sunlight or inorganic compounds into chemical energy stored in the carbon-carbon bonds of organic compounds
Principle of allocation
individuals must prioritize how to use the limited energy that is available to them. As a result, energy allocated to one of life’s necessary physiological functions will reduce the amount of energy that can be allocated to other such functions.
optimal foraging theory
Animals can adjust their energy budgets by adjusting their behavior. Applying the principle of allocation to animal foraging allows answering questions, such as ‘How much time and energy should an individual expend foraging?’, ‘What search strategy should it employ?’, ‘What types of food should it choose?’
Optimal foraging theory aims to predict the best strategies for maximizing energy intake by considering the energetic profitability of a food item
P = E/C where E= energy gained from a food item, and C= energy costs associated with acquiring and eating food
Higher values of P indicate more profitable prey items (i.e., high energetic value, low acquisition costs, or both); P=1 is a breakeven point where energy gained equals the energy invested; and P<1 indicates food items where the costs of acquiring them outweigh the energy gain
The simple energetic profitability mode, P = E/C is typically extended to separate the costs of a food item into its search costs (dependent on resource density and search strategy) and its handling costs (the combined time that it takes to capture, manipulate, consume, and digest the food);
P= E/ (S+H), where S= energy costs associated with searching for the food, H= energy costs associated with handling the food
P is maximized when energy intake is large, relative to search and holding costs
Optimal foraging theory: experimental tests
Optimal foraging theory makes quantifiable predictions that can be tested experimentally, for example, (1) foragers should prefer resources that have higher profitability, and (2) as the abundance of higher-value resources increases, consumption of lower-value resources should decrease
Temperature, a key limiting factor
Organisms can be grouped by the degree to which they control their internal temperature
Poikilotherms do not regulate their internal temperature
Ectotherms use external factors (e.g., sun, shade) to regulate their internal temperature
Endotherms use behavioral thermoregulation, plus internal processes (e.g., metabolic heat, shivering) to regulate their internal temperature
Some endotherms, called homeotherms are able to maintain their internal temperature in a very narrow range
energy budget modeling
Energy budget models can be used to estimate how an individual partitions its energy among physiological processes
When energy intake is plentiful, resources can be allocated to all processes, including growth and reproduction
When energy intake is insufficient or absent, energy needs can be met from storage. Growth and/or reproduction may cease to save energy. When the storage is depleted, the individual cannot meet its needs anymore and dies. Comparing the amount of energy that an individual has stored against its necessary daily respiration and waste costs allows estimating how long the individual can survive before it starves to death
Thermal performances curves
Temperature controls the rates of all metabolic reactions and the rates of all physiological behavioral processes (e.g., rates of movement, growth, reproduction) it is a key factor for determining the performance of organisms
Lower lethal limits: cellular respiration slows and may cease, leading the death
Upper lethal limit: cellular structures and DNA break down, leading to death
Climate envelope models
use statistical modeling to determine under what climate conditions a species currently occurs. Subsequently, they consider climate projections to figure out where those sample conditions are likely to occur in the future to determine a likely future range for the species
Step 1: record all geographic locations where the species is found
Step 2: record climate covariates at every point, and use statistical approaches to determine under what conditions the species occurs
Step 3: use climate models to determine where on the map those same climatic conditions will/will not occur in the future. The hypothesis is that this will roughly represent the new distribution of the species
Thermal performance-based population models
try to estimate where a species could occur based on its thermal constraints. Combining thermal performance curves for development rate, birth rate, death rate, and other demographic variables, can yield estimates of population growth rates under different temperature regimes. Combined with climate projections, this approach can yield estimates of where the species is likely to occur in the future
Step 1: determine the parasite’s R0 (the average number of offspring produced by an individual over its lifetime). It can be calculated from the probabilities of reaching each life stage and the fecundities at that life stage
Step 2: estimate thermal performance curves for each of the terms in the equation defining R0. This allows us to estimate how R0 varies as a function of temperature
Step 3: combine climate maps/projections without our estimate of how Ro varies with temperature to estimate how disease pressures are/will be varying across landscape. Of particular interest is hereby the R0 = 1 boundary, which separates areas with population growth (R0 > 1) from areas with population declines (R0 < 1)
