Lecture_week 10_Population dynamics

Population Dynamics

• Definition: Study of how populations change over time due to births, deaths, immigration, and emigration.

Evaluation for Test 2

• Reflective Questions:

  • Did I spend enough time learning? (Yes/No)

  • Did I focus on all topics covered? (Yes/No)

  • What materials needed more review?

  • Strategies for improvement:

    • Discuss with peers

    • Form study groups

    • Engage actively in class

    • Utilize suggested textbooks

    • Request additional resources from the instructor

  • Observations:

    • 30% of the class improved by 11-37% in Test 2.

    • Several students achieved >90% score.

    • Importance of honing listening and sharing successful strategies.

Estimating Population Size: Challenges

• Issues in detection:

  • Patchy distribution of organisms.

  • Low densities particularly in planktonic microorganisms.

Case Study: Daphnia in Base Line Lake (Hall, 1964)

Observations

• Seasonal population trends:

  • Scarce in winter

  • Abundant in late spring

  • Declining in summer

Hypothesis

• Temperature and food availability (algae) as limitations on population growth.

Research Approach

• Data collection methodology:

  • Measure Daphnia and food abundance bi-monthly over a year.

  • Estimate growth rate coefficient (r) using:

    • [ N_T = N_0 * e^{rT} ]

  • Predict birth rates (b) based on temperature and food.

  • Calculate the death rate (d) using: [ r - b = d ]

Findings of Daphnia Study

• Birth rates consistently high in summer; food (algae) not limiting.

• Interpretation:

  • Population declines due to higher mortality rates from predation rather than lower birth rates.

Life History Strategies

Goal

• Maximize biological fitness to ensure survival and reproductive success.

Example: Egg Bank in Arctic Ponds

• Limited open water period (30-60 days)

• Two reproductive strategies: A) Asexual reproduction produces resting eggs for long seasons, B) Focusing on resting egg production to ensure survival during shorter seasons.

Timing and Adaptation

• Critical seasonal timing for reproductive strategies to match local environmental conditions.

Trade-offs in Life History Strategies

1. Offspring Size vs. Number

   • Limited resources lead to fewer, larger offspring or many smaller ones vulnerable to predation.

2. Growth vs. Reproduction

   • Larger females produce more eggs.

   • Risk of dying before reproductive maturity, especially in long-lived species.

Dispersal Mechanisms

Importance of Conservation

• Need for conservation efforts in upstream source populations to support biodiversity.

Dispersal Types

1. Passive Dispersal

   • Example: Unionid mussel larvae attached to host fish.

2. Resting Stages

   • Plankton can drift with birds, aiding cosmopolitan distribution.

   • Lake Baikal as an example of high endemism.

Human Impact on Dispersal

• Example: Zebra mussels

  • Invasive species with rapid spread; importance of checking boats and trailers for transport of species.

Zebra/Quagga Mussel Distribution

• Historical data from 1986, 1990, 1994 and 2006 showcasing the expanding range across North America based on U.S. Geological Survey data.

Case Study 1: Upper Mississippi River Mussel Population

• Focus: Survival and growth of four species over four years in varied density patches.

• Methodology: PIT tagging, survival analysis in relation to substrate movement and flow dynamics (Newton et al. 2020).

Findings from Case Study

• Higher survival in areas of dense mussels; survival declines linked to increased substrate movement.

• Species-specific growth rate variations; highest in Pleurobema sintoxia.

Case Study 2: Texas Hornshell Population Dynamics

• Importance for conservation plans via long-term monitoring (1997-2012 mark-recapture study).

Observation and Hypothesis

• Mussel survival linked to flow refuges; affected more by maximum than minimum river discharge.

Protection Strategies for P. popeii

• Key factors for survival include managing groundwater withdrawal and reducing contamination risks.

Recovery Plan for P. popeii

• Stage-wise monitoring for recovery with emphasis on habitat restoration and public awareness initiatives.

• Goals include enhancing mussel populations and habitats across historical distribution.