Population Ecology: Survival Patterns

• A population is a group of individuals of a single species inhabiting a specific area
• Population density is characterized by number of individuals
• Age distributions, growth rates, distribution, and abundance provide additional characteristics

Patterns of Survival

• Cohort life table: age-specific is used as a main method of estimation
• Identify individuals born at the same time and keep records from birth

Static Life Table for Red Deer Hinds

• A table showing population data of red deer with variables like x' (age), ax, lx, dx, qx, and smoothed values

Cohort Life Table for Phlox drumondii

• A table focusing on Phlox drumondii, presenting data across different age ranges (x – x') with variables like ax, lx, dx, qx, Fx, mx, and lxmx

Main Methods of Estimation

• Age distribution tracks differences from mortality
• Difference in proportion of individuals is tracked across each age class
• Photosynthetically active radiation (bet) is a main method of estimation

Population genetics

• Population genetics is the study of genetic variation within populations, and how it changes over time

Important population genetics topics include:

• Mutations
• Gene flow
• Genetic drift
• Natural selection

Population Distribution and Abundance

• A population consists of individuals of a single species in a specific area who must be interbreeding or mating to continue generations
• Populations are characterized by the number of individuals, their density, age distributions, growth rates, and distribution
• Distribution limits are the physical environment limits geographic distribution of a species
• Organisms can only compensate so much for environmental variation

Niche

• Niche summarizes environmental factors that influence growth, survival, and reproduction of a species
• Set of factors that allows a population to sustain itself

Types of niche

• Fundamental niche: the full range of biological and physical environmental conditions, representing an ideal situation
• Realized niche: the portion of the fundamental niche hypervolume to which species are most highly adapted, often under pressure from superior competitors with overlapping niches
• Niche is not a physical space; rather, habital is just an aspect of niche

Species Distribution and Climate:

• Two species competing for the same resources result in each having a narrower realized niche than their fundamental niche in a lab setting
• Each species adapts to narrower tolerances when living together

Red Kangaroo (Macropus spp.) distributions:

• Macropus giganteus lives in eastern Australia, where there is little seasonal variation in precipitation or dominance by summer precipitation
• Macropus fuliginosus lives in southern Australia, where winter rainfall dominates
• Macropus rufus lives in central and western Australia, where conditions are hot and dry

Distribution limits

• Climate may influence species distribution indirectly via food production, water supply, habitat, and incidence of parasites, pathogens, and competitors

Tiger Beetle (Cicindela longilabris)

• Tiger Beetles live at higher latitudes and elevations than most other species in North America
• Distribution is across North America in cool, moist habitats
• Distribution in the far north of North America: boreal forests
• Distribution south of boreal forests: high mountain forests and meadows

Species distribution

• Bush Sunflowers (Encelia spp.) distribution corresponds to variations in temperature and precipitation
• Ecotypes are organisms that belong in the same species, but live in different environmental conditions

Ecotypes

• Encelia californica lives on the coast of California and Baja California, experiencing cool, moist conditions in the north and cool, dry conditions in the south
• Encelia actoni lives farther inland, with drier and slightly warmer conditions
• Encelia farinosa and Encelia frutescens exist even farther inland where it's hotter, and their geographic distributions overlap greatly

Barnacles

• Barnacles show distinctive patterns of zonation
• Chthamalus stellatus occupy upper levels and compete with big Balanus barnacles which excludes Chthamalus stellatus from lower areas
• Competition is an absolute resource where that cannot be shared (e.g. space)
• Balanus balanoides occupy middle-lower levels and are more vulnerable to desiccation as they are excluded from upper intertidal zone and don't prefer sunlight
• Zones are differentiated via tides
• Upper intertidal zone is less covered by tide
• Lower intertidal zone is almost always covered by water

Important to note:

• Movement happens from zone to zone via water movement

Distributions of Individuals on Small Scales

• Random distributions have an equal chance of being anywhere as a result of neutral interactions and uniform distribution of resources
• Regular distributions are uniformly-spaced as a result of exclusive use of areas, antagonistic interactions, and allelopathy
• Clumped distributions have an unequal chance of being anywhere as a result of mutual interactions, mutual attraction between individuals to a common resource and patchy resource distribution

Distribution of Individuals on Large Scales

• Bird populations across North America showed clumped distributions in Christmas Bird Counts
• Clumping occurs in species with widespread distributions, patchy resources, and few densely populated study sites

Plant Distributions

• Woody plants are distributed along moisture gradients in North American mountain ranges: moisture gradient: moist canyon bottoms to dry southwest-facing slopes
• Highly clumped distribution occurs in plants distributed along moisture gradients
• Distribution substantially decreases towards the edges

Key plant species in the mountain region

• Table mountain pine: drier, high slope
• Red maple: middle slope
• Hemlock: moister, low slope

Mange Distribution

• Before the outbreak, mountain hares fluctuated between about 30,000 and 60,000
• Mange increased Dramatically and mange reduced the fox
• Year of mange 1965 to 1990

Snowshoe Hares:

• Live in boreal forests dominated by conifers and dense growth of understory shrubs
• In winter, browse on buds and stems of shrubs/saplings e.g. aspen, spruce
• Shoots produced after heavy browsing increase Level of plant chemical defenses
• Lynx are classic specialist predator
• Starvation, Weight loss leading to increased predation = decrease populations

Herbivory:

• Organisms use chemical defenses - plants use quantitative ingested which prevents digesition, and qualitative - Kills herbivore