Intraspecific Variation, Ecomorphology, and Conservation

The Ecology of Intraspecific Variation, Ecomorphology, and Conservation

Morpho-genetic Changes Across a Varying Landscape

Patterns of Local Environmental Variation

  • Environmental conditions are not universally diverse; instead, they are heterogeneous across a landscape, giving rise to different habitats.

  • The four most important ecological aspects of habitat discontinuity are:
      - Magnitude of Differences: The size of the differences between habitats.
      - Degree of Isolation: The extent to which the habitats are isolated from each other (e.g., islands or mountain tops).
      - Relative Sizes of Habitats: The size comparison between different habitats.
      - Merging of Habitats: The degree to which habitats blend into one another where they contact, such as montane upland savannah merging with desert.

Effects of Habitat Size on Species Variation

  • Habitat size plays a crucial role in affecting variation within a species.

  • Course-Grained Environmental Variation:
      - A species occurs across many habitats.
      - Example: Side-blotched Lizard (Uta stansburiana) occurs across various habitats from the desert floor to mountain tops.

  • Fine-Grained Environmental Variation:
      - A species occurs in fewer habitats, possibly even in just one.

Effects of Habitat Size Variation

  • Habitat size affects variation within a species.

  • Course-grained environmental variation demonstrates adaptive behavior and morphology across habitats, which has implications for conservation management.

  • Example of Side-Blotched Lizard:
      - Occurs within all habitats across a 50–100 km distance, showing morphological and behavioral adaptations suited to those habitats.

Zebra-Tailed Lizard

  • Occurrence: Found only in the Lower Sonoran Desert.

  • Provides a case for fine-grained environmental variation:
      - Occurs in fewer habitats, with behaviors that are generally stable due to less environmental variability.
      - Management programs for this species are less complicated because of its habitat specificity.

  • The Zebra-tailed Lizard (Callisaurus draconoides) shows variation across approximately 650 km but remains adapted to the same desert habitat.

Geographic Variation Within a Species

  • Environmental factors vary between habitats, causing natural selection to induce genetic, morphological, and ecological variations between populations.

    • Natural selection induces genetic variations as well as morphological and ecological ones as well.

  • California Kingsnake (Lampropeltis getula):
      - Shows variations between populations in desert vs. coastal habitats.

  • Clinal Variation:
      - Defined as a continuous change in characteristics across a broad geographic area.
      - Variation corresponds with environmental factors:
        - Cool and Wet: Produces darker-colored organisms.
        - Hot and Dry: Produces lighter-colored organisms.
      - Example: Size and color vary from small, light individuals in the east to large, dark individuals in the west.

Step-Clinal Variation

  • Represents rapid changes over a narrow geographic area and results from significant environmental changes.

  • Example of Rosy Boa (Lichanura trivirgata):
      - Exhibits defined patterns such as:
        - Southern Baja California: dark-brown stripes in subtropical areas.
        - Central Baja California: brownish to orange stripes in arid regions.
        - Northwestern Baja California: grayish with poorly defined stripes in cooler coastal areas.

Could this be result of natural disaster in an area?

do coarse grain and fine grain go hand in hand with clinal and step clinal variation?

Patterns of Morphological Variation Across Archipelagos

  • Geographic variation on islands can promote speciation as seen in the Uta species complex consisting of:
      - Uta squamata on Santa Catalina Island.
      - Uta nolascensis on San Pedro Nolasco Island.
      - Uta stansburiana on Tortuga Island.
      - Each species has diverged due to isolated ecological niches.

Case Studies on Genetic Variation

  • Case Study 1:
      - Geographically Structured Genetic Variation with Gene Flow in Western Banded Gecko (Coleonyx variegatus):
        - Demonstrates gene flow among various populations indicating they belong to a single species.

  • Case Study 2:
      - Geographically Structured Genetic Variation in Absence of Gene Flow in Parachute Geckos (Gekko):
        - No gene flow among populations implies they are different species

    • No gene flow results in speciation

  • Comparative Analysis:
      - Coleonyx variegatus remains a single species showing morphological variation yet capable of interbreeding.
      - Gekko displays speciation influenced by historical environmental barriers, resulting in limited reproductive cohesion.

Ecotones

  • Defined as transitional boundaries between different habitat types; they may be abrupt or gradual.

  • Example:
      - The boundary between a river and adjacent land (abrupt).
      - A coastal rainforest merging into a lowland rainforest (gradual).

Adaptations within the Local Environment

  • Case Study 3:
      - Local Substrate Matching in the Desert Horned Lizard (Phrynosoma platyrhinos):
        - Populations show inter-fertility despite morphological differences found within 100 m of each other.
                           

  • Case Study 4:
      - Regional Substrate Matching in Banded Rock Lizard (Petrosaurus repens):
        - Despite morphological differences across 570 km, all populations are inter-fertile.

Ecomorphology

  • Defined as body shape and behavior adapted to specific lifestyles in particular habitats (e.g., arboreal vs. fossorial).

  • Indicates how closely tied a species is to its environment.

  • Convergent Evolution:
      - Similar ecomorphs can evolve in unrelated species.
        - Example: Arboreal gibbons vs. fossorial gophers show similar adaptations to their environments based on lifestyle needs.

Factors Favoring the Evolution of Ecomorphs

  • Sufficient genetic variation in the trait:
      - Fundamental Fisher's Theorem: Rate of increase in mean fitness due to natural selection is equal to the additive genetic variation affecting fitness.

  • Intensity of natural selection on that trait and geographical barriers to gene flow can impact the formation of genetically isolated ecomorphs.

  • Examples: Cactus Wren, White-winged Dove, Ring-bill Gull.

Intraspecific Variation in Coral Reef Fish

  • Damsel Fish (Acanthrochromis polyacanthus): Highly variable fin morphology related to habitat, affecting speed and escape tactics.

  • Fish in high-exposure environments develop greater aspects of caudal fins providing them with faster swimming capabilities.

  • Conservation Implications: Genetic separation due to habitat preferences may lead to a lack of interbreeding if populations remain isolated due to predation pressures.

Tiger Geckos of Northern Vietnam

  • Composed of five species, with four karst-adapted and one granite stream-adapted species (Goniurosaurus huiliensis, Goniurosaurus lichtenfelderi).

  • Grouping is based on body shape corresponding to ecological pressures.

  • Convergent evolution due to adaptation to specific environments is observed in these geckos.

    • through what?

Factors That Create and Maintain Genetic Variation

  • Sources of Genetic Variation:
      - Mutations as ultimate sources of genetic diversity—primarily point mutations affecting single DNA bases.
      - Recombination introduces genetic differences through sexual reproduction by shuffling alleles from parents to offspring.

How Genetic Variation is Preserved

  • Diploidy protects unfavorable alleles from selection by hiding them in recessive forms, allowing their transfer across generations through heterozygotes.

  • Balanced Polymorphism: Maintains variation through advantages conferred by heterozygous individuals (e.g., sickle-cell anemia) where carriers have survival advantages in certain environments.

  • Neutral Variation: Some traits, like human fingerprints, persist without selection due to being neutral.

  • Understanding these mechanisms of variation is crucial for conservation planning and ecological management strategies.