noc19-bt09 Lecture 13-population parametersand demographic techniques

Population Ecology Module Overview

Introduction to Population Ecology

• The module on Population Ecology consists of three lectures: population parameters and demographic techniques, population growth and regulation, and applications of population studies.

Understanding Demography

• Demography is defined as the study of populations, where "demo" refers to people and "graphy" means to write. This field focuses on methods for describing populations.

Definition of Population

• A population is defined as all organisms of the same species living in a specific geographical area capable of interbreeding. Examples include populations of impalas and cheetahs in Africa.

Importance of Population Parameters

Reasons for Studying Population Parameters

• Understanding population parameters is crucial for regulating species and comprehending natural phenomena. For instance, increasing impala populations can support predator populations like cheetahs or lions.

Equation for Population Dynamics

• The basic equation governing population change is P(n+1) = P(n) + natality + immigration - mortality - emigration. This equation accounts for births (natality), incoming individuals (immigration), deaths (mortality), and outgoing individuals (emigration).

Management Stages in Population Studies

PDCA Cycle in Management

• Effective management follows the PDCA cycle: Plan, Do, Check, Act. Each stage involves planning interventions based on population data, implementing those plans, checking their effectiveness, and making necessary adjustments.

Planning Stage

• In the planning phase, strategies are developed to increase tiger populations by ensuring adequate prey availability and disease control.

Implementation Stage

• The doing stage involves executing the planned actions aimed at improving wildlife management outcomes.

Checking Stage

Understanding Population Management Through the Deming Cycle

The Acting Stage in Population Management

• The acting stage follows the checking stage, where decisions are made based on population assessments. For example, if tiger populations are increasing, one might consider increasing chital numbers to support further growth.

• If tiger numbers are decreasing due to poaching, a new plan must be developed to address this issue. This iterative process is part of the Deming cycle: planning, doing, checking, and acting.

Importance of Numerical Data in Decision Making

• Accurate population data is essential for effective management. Understanding current tiger populations and desired targets is crucial for making informed decisions about conservation efforts.

• Decisions regarding whether to increase or decrease tiger populations depend heavily on numerical assessments. Without these figures, it’s challenging to determine necessary actions.

Assessing Risks of Population Decline

• Assessments help identify risks associated with low population numbers. For instance, having only four male tigers could lead to extinction if no females are present for breeding.

• Evaluating probabilities related to demographic stochasticity (random variations in births and deaths) is vital for understanding potential population crashes.

Environmental Stochasticity and Its Impact

• Environmental stochasticity refers to unpredictable environmental events that can drastically affect populations. Understanding these risks helps in preparing for potential crises like drought or disease outbreaks.

• An example illustrates how a forest fire could decimate a small population but may leave larger populations intact enough to survive despite significant losses.

Conclusion on Population Assessment Necessities

• To effectively manage wildlife populations, understanding both original sizes and potential impacts of environmental changes is critical. This knowledge aids in predicting survival chances during adverse conditions.

Understanding Population Dynamics and Genetic Issues

Genetic Problems in Small Populations

• A small population size can lead to high homozygosity, resulting in genetic problems such as inbreeding depression and loss of heterozygosity.

• Behavioral issues may arise alongside genetic problems, particularly the Allee effect, where individuals cannot perform essential biological functions effectively due to low numbers.

The Allee Effect in Wild Dogs

• In pack-hunting species like wild dogs, a larger group allows for effective hunting strategies; smaller packs struggle to hunt efficiently. For example, a pack of 50 can spare individuals for protection while hunting.

• If the pack size is reduced to 10 adults with many young ones left unprotected during hunts, it increases vulnerability to predators like leopards, leading to potential population collapse.

Implications of Population Size on Survival

• The Allee effect manifests when populations are too small (e.g., 10 individuals), hindering their ability to find mates or hunt effectively compared to larger groups (e.g., 50 individuals). This highlights the importance of maintaining adequate population sizes for survival.

• Understanding whether a population is at risk from behavioral or genetic issues necessitates accurate population assessments, which are crucial for conservation efforts.

Scenario Planning and Risk Assessment

• Effective planning involves assessing probabilities of environmental threats (drought, disease) over time and understanding how these factors could impact population viability. For instance, drought probability might be assessed at 25%.

• By simulating various scenarios based on these probabilities (e.g., drought followed by disease), one can evaluate potential outcomes for the population's future stability and identify necessary interventions if risks are high.

Strategies for Mitigation and Adaptation

• If assessments indicate a high likelihood of population decline (e.g., a 10% chance of crashing within ten years), proactive measures must be taken—such as increasing individual numbers or enhancing protections against diseases and environmental threats.

Population Assessment and Management Strategies

Understanding Disease Mitigation in Animal Populations

• Discusses the importance of vaccinations and mitigation strategies to help animals fend off diseases, including analyzing and addressing the causes of disease spread.

Importance of Population Size and Trends

• Highlights that assessing population size is crucial; distinguishing between raw numbers (e.g., 2500 tigers) and trends (e.g., increase or decrease over time) is essential for effective management.

Analyzing Population Trends vs. Numbers

• Emphasizes the need for both absolute numbers and trends to understand population dynamics, particularly for species like tigers where exact counts are vital compared to prey species like chital.

Population Parameters: Size vs. Density

• Defines population size as the total number of individuals in a given area, contrasting it with population density, which measures individuals per unit area (e.g., tigers per square kilometer).

Variability in Population Density Across Species

• Explains how different organisms exhibit vast differences in density; for example, diatoms can be found at millions per cubic meter while larger mammals like humans have much lower densities.

Methods for Measuring Absolute Density

• Outlines three methods for measuring absolute density:

• Total count: Directly counting every individual.

• Sampling method: Estimating populations through representative samples.

Understanding Sampling Methods in Wildlife Studies

Introduction to Estimating Animal Populations

• The estimation of animal populations can be achieved through various methods, although some may not be applicable in specific contexts, such as India where animals are not killed for study.

Quadrat Sampling Method

• Quadrats can take different shapes: square, rectangular, circular, or even irregular. The choice of shape impacts the sampling process.

• Effective sampling aims to represent the entire population accurately by capturing key characteristics across different areas.

Importance of Representative Sampling

• A single sample from a high-density area could lead to significant underestimation if extrapolated over a larger area.

• To avoid bias, samples should reflect the density distribution; for example, if 40% of an area has high density, then 60% of samples should come from that region.

Defining Sampling Units

• Sampling units can be administrative (like compartments), natural (topographical sections), or artificial (defined plots). Each unit must allow for clear observation and data collection.

Creating a Sampling Frame

• A sampling frame is essentially a list of all potential sampling units. From this frame, specific units are selected based on defined criteria.

Understanding Sampling Intensity

• Sampling intensity is calculated as the ratio of sampled units to total population units. Higher intensity leads to more accurate representations; full inclusion results in a census.

Types of Plots and Their Applications

• Plots can vary in shape and size; they may include topographical divisions based on elevation or other geographical features.

Overview of Different Sampling Techniques

• Various sampling techniques exist including simple random sampling, systematic sampling, stratified sampling, multistage sampling, and probability proportional to size.

Sampling Techniques in Research

Simple Random Sampling

• Simple random sampling involves selecting a specific number of units (e.g., 5) from a larger sample (e.g., 39). Each unit has an equal probability of being chosen, which is calculated as 1 in 39.

• This method can be executed through various means such as lotteries or random number generation.

Systematic Sampling

• Systematic sampling selects every kth unit from the population, starting with a randomly chosen unit between 1 and k.

• For example, if every 5th unit is selected, the first unit is picked at random (e.g., the 3rd), followed by units like the 8th, 13th, etc.

• This approach ensures that samples are evenly distributed across the population.

Stratified Sampling

• Stratified sampling divides a heterogeneous population into subpopulations known as strata, which are internally homogeneous.

• By taking small samples from each stratum, researchers can obtain precise estimates for each group and combine them for an overall estimate of the entire population.

• For instance, if studying forest areas with varying densities, different samples would be taken from high-density and low-density regions to ensure accurate representation.

Multistage Sampling

• Multistage sampling involves selecting large units first (e.g., states), then choosing smaller subunits (e.g., districts) within those large units.

• An example includes randomly selecting five states and then five districts from each state to form a comprehensive sample.

Probability Proportional to Size Sampling (PPS)

• PPS sampling assigns probabilities based on the size of the units involved. Larger units have higher chances of selection when their size correlates with the variable under study.

Understanding Population Density Measurement

Overview of Sampling Methods

• The discussion begins with the measurement of absolute population density, focusing on two primary methods: counts and sampling techniques.

• One sampling method introduced is the capture-recapture method, which estimates fish populations in a pond by marking captured individuals.

Capture-Recapture Method Explained

• In this method, after capturing and marking 50 fish with red dye, they are released back into the pond to mix with unmarked fish.

• A second sample of 50 fish is taken later; if 10 are marked, it indicates that one out of every five fish in the pond is marked. This leads to estimating a total population size based on proportions.

Key Assumptions of Capture-Recapture

• The formula used for estimation relies on several assumptions: random capture of marked and unmarked animals, equal mortality rates among both groups, and permanence of marks.

• If marked fish die at a different rate than unmarked ones or lose their marks, estimations will be inaccurate.

Introduction to Removal Method

• The removal method involves killing or removing animals from a population while adhering to specific assumptions about immigration/emigration and birth/death rates during the study period.

• It emphasizes that removed animals must not return to the environment and that traps should only catch one species at a time.

Proportionality in Animal Removal

• This method states that the number of animals removed per unit effort correlates directly with their initial population size; thus, as populations decrease, fewer can be caught.

Estimating Animal Population Density

Relative Population Density Methods

• The focus is on determining which area (X or Y) has a higher number of animals through various methods.

• Trapping animals in different areas allows for direct comparison of capture rates to infer population density.

• Observing the number of sounds made by tigers can indicate relative population sizes; more calls suggest a larger population.

• Other methods include pelt counts, catch per unit effort in fishing, and assessing the number of nests or sightings reported by field staff.

• Analyzing plant cover and feeding capacity can also provide insights into animal populations based on resource availability.

Understanding Population Metrics

Age Pyramid and Reproductive Rates

• The age pyramid reveals the distribution of age groups within a population, indicating whether it is predominantly young, adult, or old individuals.

• Crude birth rate measures live births per 1000 individuals annually; crude death rate measures deaths per 1000 individuals.

• General fertility rate focuses on live births per 1000 females of reproductive age; specific fertility rates target particular age classes among females.

• Replacement level fertility assesses how many offspring are needed to maintain population size; producing fewer than two leads to decline while producing more increases numbers.

Mortality and Longevity Insights

• Juvenile mortality rates track deaths among young animals per 1000 live births; life expectancy indicates average lifespan at current mortality levels.

• Physiological longevity refers to lifespan under ideal conditions, while ecological longevity considers real-world factors like predation and disease affecting survival rates.

Migration and Growth Dynamics

Key Factors Influencing Population Changes

• Immigration adds individuals from outside sources while emigration removes them; net migration is calculated as immigration minus emigration.

• Natural increase in population is determined by subtracting deaths from births; overall growth includes immigration effects as well.

• Growth rate expresses changes over time either as a percentage or absolute numbers annually, emphasizing the need for precise data collection.

Importance of Measurement Accuracy

Understanding Precision and Accuracy in Measurements

The Concepts of Precision and Accuracy

• Measurements can be classified as precise or imprecise based on how close the values are to each other. A small range indicates precision, while a large range signifies imprecision.

• Accuracy refers to how close a measurement is to the actual value. For example, if the true length of an object is 12 centimeters, measurements that closely align with this value are considered accurate.

• If a method estimates 1000 individuals but reports only 500, it lacks accuracy. Conversely, reporting 1005 individuals would indicate a more accurate method.

Visualizing Precision and Accuracy

• An analogy using shooters illustrates these concepts: shots clustered together indicate precision; however, being far from the target center reflects inaccuracy.

• A shooter may have precise shots (close together) but still miss the target (not accurate). Alternatively, some shots may be spread out yet average near the target center (accurate but imprecise).

Understanding Bias and Calibration

• Bias occurs when measurements are consistent among themselves but deviate from the actual value. This discrepancy necessitates calibration to correct for bias.

• To reduce bias in population measurements, methods like total census can be employed instead of capture-recapture techniques that might introduce significant bias.

Importance of Population Measurement Techniques

• Accurate population measurement is crucial not just for ecological studies but also for effective management and conservation strategies.