AEC 360    Ecology

Lecture 5:  What limits plant and animal distributions?

I.  Factors that limit species distributions in terrestrial environments
    A.  Precipitation and the rain shadow (Fig. 5.4)

        1.  Variation in precipitation affects the local distribution of species (Fig. 18.6)

     B.  Variation in soils can influence the local distribution of species (Fig. 5.17)
        1.  Vertical stratification of soils into horizons, from the O-horizon (organic topsoil) to C-horizon (bedrock)

        2.  Horizontal differences in levels of soil nutrients affect local species distributions

    C.  Variation in temperature limits species ranges

    D.  Species can be limited in their distributions by the presence of other species 

        1.  The distribution of cattle is limited by the distribution of tsetse flies

    E.      Niche The range of conditions a species can tolerate  (Fig. 11.2)

        1.  Fundamental niche

        2.  Realized niche

        3.  Niche modeling to predict future distributions 

II.  Factors that limit species distributions in aquatic environments
    A.  Include physical factors such as Salinity, Light Penetration, and Temperature
        1.  Definitions: Nutrients
            a. Oligotrophic: nutrient limited
            b. Eutrophic: nutrient rich
        2.  Definitions:  Water flow
            a. Lotic: moving water like streams
            b. Lentic: standing water like lakes

    B.  Streams vary from headwaters to the river mouth:  The River Continuum Concept
        1.  Headwaters dominated by inputs from leaves, cold, oxygenated water
            a.  insects include shredders and collectors
            b.  fish include species that are adapted to cool, oxygenated water

        2.  Downstream dominated by internal primary production, warm, oxygen-poor water
            a.  insects include collectors
            b.  fish include species adapted for warm, less-oxygenated water

    C.   Feeding adaptations in streams
        1.  In lotic habitats, some fish species are adapted to capture prey moving past them in the current
            - faster currents bring more food but require more energy expenditure to maintain position

        2.  In lentic habitats, some fish species have external taste buds on specialized structures that allow them to sense food in turbid environments

    D.  Within a lake, light and temperature influence distributions of species  (Fig. 6.15, 6.16)
        1.  The littoral zone is the area near the shore where light can reach the lake bottom and allows plants to grow

        2.  The limnetic zone is the open water, and varies with depth
            a.  The epilimnion is the upper layer where light penetrates and warms the water

            b.  The hypolimnion is the deeper, cooler part of the lake

            c.  The thermocline separates the epilimnion and hypolimnion

            d.  Lake stratification determines the location of the thermocline, and mixes the lake (Fig. 6.16)

        E.  Lentic habitat: Wetlands and adaptation: Breeding in ephemeral ponds

            - many amphibians are adapted to breed in ephemeral ponds
            - major benefit (versus breeding in permanent habitat) is lack of fish predators
            - invertebrates are also very abundant in these habitats
            - rapid egg and larval development

        F.  Like in lakes, species distributions in oceans are determined by light and temperature (Fig. 6.22)
            1.  The photic (the surface) and aphotic (deeper, cooler, darker) zones demarcate distributions

III.  Physical barriers limit continental and global distributions of species

   A.  Can see limits by how they are overcome by human-introduced species