Abiotic Factors Affecting Species Distributions - Study Notes

Abiotic Factors Affecting Species Distributions – Study Notes

  • Overview

    • Abiotic environment influences organisms over two timescales:
    • Over many generations: affects natural selection
    • Over shorter periods: affects resource availability and organism’s physiology
    • Distinguishing weather vs climate:
    • Weather: conditions at a specific time/place (temperature, humidity, precipitation, wind, cloudiness, etc.)
    • Climate: long-term average patterns of weather (local, regional, global)
    • Weather patterns are influenced by solar radiation, the atmosphere, and Earth's rotation and movement.

  • Solar radiation and the Earth’s energy budget

    • Solar radiation is electromagnetic energy; hotter objects emit shorter wavelengths with higher energy.
    • Average Net Radiation is zero: ext{Average Net Radiation} = 0
    • About half of solar radiation reaching the atmosphere is absorbed; half is reflected and scattered by atmosphere and clouds.
    • The amount of solar radiation that reaches the surface (insolation) varies with latitude.
    • High latitudes receive sunlight at a steeper angle and over a larger air column, leading to more scattering and reflection; the equator receives solar radiation more directly over a shorter distance.
    • Conceptually, the Earth’s energy budget explains latitudinal temperature gradients and climate patterns.

  • Latitudinal variation in insolation and surface temperatures

    • Equator: solar radiation strikes surface at a more direct angle, concentrated over a smaller area.
    • High latitudes: solar radiation strikes at a steeper angle, over a larger area, through more atmosphere and scattering.
    • Net radiation (incoming minus outgoing) varies by latitude, contributing to regional climate differences.
    • Figure reference notes: typical representations show shortwave (incoming) vs longwave (outgoing) radiation across latitudes.

  • Diurnal and seasonal cycles

    • Earth’s rotation: ~1 day per rotation, causing day/night cycles.
    • Earth’s orbit around the Sun: ~1 year; axis tilt = 23.5° (constant tilt during orbit).
    • Axial tilt causes seasonal variation in insolation, greater with increasing latitude.
    • Florida latitude range: approximately 25°N to 31°N (illustrates mid-latitude seasonality).
    • Seasonal variation in insolation leads to latitude-dependent seasonal productivity and species responses.

  • Day length, seasonality, and organismal timing

    • Diurnal cycle (hours of daylight) varies with season globally except at the equator (where day length is ~12 h year-round).
    • Day length changes with season strongly affect activity schedules and productivity.
    • Impacts on foraging time in winter and bird abundance across latitudes.
    • Example: Crested tits (Lophophanes cristatus) in Spanish juniper woodlands show higher abundance at latitudes with longer day-lengths due to more foraging time on juniper fruits.
    • Winter day-length variation example: difference of ≈10.5 minutes over ~190 km in latitude; cumulative effect ≈13.5 additional hours available for foraging over the entire winter season, influencing energy budgets of small birds.
    • Seasonal cues for reproduction: day-length can cue breeding in some species (e.g., Brown-headed Cowbirds, Molothrus ater, use day-length as a breeding cue).

  • Seasonal changes in appearance and body size with latitude

    • Seasonal color morphs in insects (e.g., Anartia jatrophae – White Peacock butterfly): dry season (winter) form vs wet season (summer) form differ in size and color; dry season form tends to be larger and paler, wet season form smaller and darker.
    • Arctic fox (Alopex lagopus) changes fur color across seasons to blend with snow in winter and vegetation in summer.
    • Bergmann’s rule (principle for endotherms):
    • In colder climates, smaller surface-to-volume (S/V) ratios help conserve body heat (favors larger body size to reduce heat loss).
    • In warm climates, higher S/V ratios aid heat dissipation (favors smaller body size).
    • Bergmann’s rule applies mainly to birds and mammals.
    • Example: Neotoma cinerea (busy-tailed woodrat) distribution ranges from Arctic Canada to northern New Mexico & Arizona; body size tends to increase with latitude (larger in the Arctic).

  • Climate, coloration, and biogeography in insects

    • Climate can affect latitudinal and color distribution of insects (e.g., butterflies).
    • Wing color in butterflies is used to regulate body temperature: warmer climates favor lighter wings; cooler climates favor darker wings.
    • Species ranges are shifting due to climate change, with shifts toward higher latitudes (northward in the Northern Hemisphere).

  • Species distribution in relation to temperature, moisture, and life cycles

    • Temperature and moisture levels can affect any stage of an organism’s life cycle:
    • Survival
    • Reproduction
    • Development of offspring
    • Interactions with other organisms
    • Key question: Which abiotic factor is most important for distribution? Is it maximum, minimum, average, or variability? This is difficult to determine and may depend on the species and context.

  • Other abiotic factors influencing distribution

    • Beyond climate, many abiotic factors can influence distributions:
    • pH
    • Nutrient availability
    • Salinity
    • Habitat type / soil composition
    • Topography
    • Wind
    • Fire
    • Examples:
    • Eastern Spadefoots (Scaphiopus holbrookii) prefer dry habitats with sandy soil; breed in fishless ponds, roadside ditches, and large potholes.
    • Salinity can affect the distribution of coastal plants.
    • pH can affect terrestrial plant distributions; pine needles promote acidic soils, allowing only acid-tolerant plants to grow.

  • Microclimates as local-scale determinants

    • Definition: microclimates are localized climate differences within a small area that cause temperature, moisture, and other conditions to differ from the surrounding area.
    • Important determinants on a local scale include:
    • Soil temperature
    • Soil moisture
    • Wind movement
    • Evaporation
    • Vegetation

  • Microclimate Think-Pair-Share activity (conceptual takeaway)

    • Suggested discussion prompts:
    • Examples of two microclimates experienced in the same area (yard, park, beach, etc.).
    • How microclimate variation could lead to greater biodiversity in an ecosystem.
    • Approaches ecologists use to determine which abiotic factors influence distribution and organism responses:
    • 1) Natural experiments: no manipulation of variables; select sites and observe data on various variables.
    • 2) Field experiments: study natural communities with manipulation of one or a few factors (e.g., introductions or removals).
    • 3) Laboratory experiments: synthetic habitats or communities; strict control of abiotic and biotic environments.
    • Which approach is best? There is no single best method; each has advantages and disadvantages depending on:
    • Spatial and temporal scale
    • Type of organism and life history/mobility
    • Realism and practicality of controlling/measuring variables
    • Practical takeaway: a combination of all three approaches is often needed to determine patterns and processes.

  • Connections to broader topics

    • The abiotic factors described here set the stage for understanding adaptation and natural selection (Ch 5 in the referenced course materials).
    • Understanding distributions helps explain ecological niches, range shifts under climate change, and species interactions under varying environmental constraints.

  • Practical implications and takeaways

    • Predicting species distributions requires considering multiple abiotic factors (temperature, moisture, pH, salinity, wind, soil type, microclimates).
    • Small-scale variation (microclimates) can create refugia and promote local diversity even within a relatively uniform region.
    • Climate change can alter insolation patterns, day-length cues, and life-cycle timing, leading to shifts in species ranges and phenologies.

  • Key terms to remember

    • Weather vs Climate
    • Insolation and net radiation
    • Latitude and insolation patterns
    • Diurnal cycle and seasonality
    • Bergmann’s rule
    • Microclimate
    • Natural, field, and laboratory experiments
    • Abiotic vs biotic factors

  • Equations and numerical references to recall

    • Average Net Radiation: ext{Average Net Radiation} = 0
    • Half of solar radiation absorbed vs reflected: rac{1}{2} ext{ absorbed}, rac{1}{2} ext{ reflected}
    • Axial tilt (for seasons): heta = 23.5^{\circ}
    • Day length at equator: ext{Day length}_{ ext{equator}}
      ightarrow 12 ext{ hours}
    • For the Red Kangaroo distribution: distribution set by a rainfall contour of about R \approx 400 ext{ mm}
    • Seasonal day-length change example: difference of ≈10.5 ext{ minutes} over ≈190 ext{ km}; cumulative for winter ≈13.5 ext{ hours} of potential foraging time
    • Bergmann’s rule basis: larger body size in colder climates to reduce heat loss; smaller size in warmer climates to dissipate heat

  • Suggested additional readings and preparation

    • Read Chapter 5: Adaptation & Natural Selection to connect abiotic factors with evolutionary responses.
    • For Discussion 1: find scientific articles on Plant/Animal adaptations; article due 8/31; group presentations 9/9.