Population Dynamics and Structures

Population Age Structure

• Describes the relative number of individuals in each age class within a population
• Important for understanding a population's growth potential and future trends

Survivorship

• Age-specific survivorship represents the proportion of individuals alive at the beginning of an age interval that survive until the start of the next age interval.

Sex Ratio

• Important for understanding potential population growth, especially focusing on females since they are the ones who give birth.

Population Growth

• Increases in population size are primarily influenced by birth, death, immigration, and emigration.

Cohort

• A group of individuals born at the same time and belonging to the same species and population

Survivorship Curves

• Type III: Characterized by high juvenile mortality followed by low mortality once offspring reach a critical size.
  • This type of survivorship is common for species that produce large numbers of offspring with little parental care.

Per Capita Birth Rate (b)

• Represents the number of births per individual in the population.

Carrying Capacity (K)

• The maximum population size that an environment can sustainably support, given the available resources.

Carrying Capacity and Logistic Model

• The logistic model of population growth incorporates carrying capacity (K) and intraspecific competition.

Intraspecific Competition

• Competition for limiting resources between individuals of the same species.
  • This competition can limit population growth as individuals struggle for food, water, space, and other resources.

Per Capita Growth Rate (r)

• If the per capita growth rate (r) is greater than zero (r > 0), it indicates that the population is growing.
  • If r is less than zero (r < 0), the population is decreasing.
  • If r is equal to zero (r = 0), the population is stable.

Plant Evolution and Diversity

• Plants are multicellular, photosynthetic eukaryotes, with at least 400,000 living species, including approximately 24,000 in Southern Africa.
• Plants evolved from freshwater green algae (chlorophyta) about 475 million years ago (mya).
• The most likely algal ancestor of plants is charophyte algae.

Adaptations to Land

• Protection Against Desiccation:
  • Cuticle: A waxy outer layer that slows water loss and prevents drying out.
  • Stomata: Tiny openings in epidermal surfaces that allow for gas exchange and prevent direct exposure of moist cell surfaces to the atmosphere. Stomata are formed by guard cells that can open and close the space between them.

Transition From Water to Land

• Water Environment:

  • Water is plentiful, making desiccation a non-issue.
  • The plant body is supported by the water.
  • Light availability can be limited.
  • CO2 availability and diffusion is restricted.

• Land Environment:

  • Water is scarce, making desiccation a serious problem.
  • The plant body lacks support from the surrounding environment.
  • Light is readily available.
  • CO2 is plentiful.

Major Plant Groups

• Bryophytes (Nonvascular):

  • Liverworts (Hepatophyta)
  • Mosses (Bryophyta)
  • Hornworts (Anthocerophyta)
  • Features: Lack vascular tissues and lignin, rhizomes, gametophyte dominant, gas exchange via pores.

• Seedless Vascular Plants:

  • Club mosses (Lycophyta)
  • Ferns, whisk ferns and horsetails (Monilophyta)
  • Features: Swimming sperm, no seeds, heterospory and homospory.

• Seed Plants (Spermatophyta):

  • Gymnosperms
  • Angiosperms
  • Features: Nonswimming sperm in pollen, seeds, heterospory, vessel elements in angiosperms.

• Tracheophyta (Vascular):

  • Features: Apical meristem, stomata that open and close, lignin, tracheids, vascular tissues (xylem, phloem), root and shoot systems, sporophyte dominant.

Key Adaptations for Land Life

• Protection from desiccation (drying out).
• Mechanism for taking up water and minerals.
• Mechanism for transporting water and minerals.
• Support tissue to keep plants upright and expose photosynthetic surfaces.
• Reproduction in a dry environment.
• Effective dispersal without water.