Introduction to Population Ecology PDF

POPULATION ECOLOGY Ms. Denisse Kate R. Almanon, M.Sc. Natural Science and Mathematics Cluster School of Arts and Sciences Ateneo de Davao University POPULATION AS A UNIT OF STUDY Population A group of organisms of the same species occupying a particular spa...

POPULATION ECOLOGY Ms. Denisse Kate R. Almanon, M.Sc. Natural Science and Mathematics Cluster School of Arts and Sciences Ateneo de Davao University POPULATION AS A UNIT OF STUDY Population A group of organisms of the same species occupying a particular space at a particular time Demes Groups of interbreeding organisms, the smallest collective unit of a plant or animal population POPULATION AS A UNIT OF STUDY Population has group and not individual characteristics Basic characteristics of a population: – Density (no/area; no/vol) – Size (numbers) – Age Structure (based on age distribution) – Dispersion (the spread of individuals in relation to one another) BASIC POPULATION PARAMETERS Density Number of organisms per unit area or per unit volume Natality The reproductive output of a population (birth, reproduction) BASIC POPULATION PARAMETERS Mortality The death of organisms in a population Immigration The number of organisms moving into an area occupied by the population BASIC POPULATION PARAMETERS Emigration The number of organisms moving out of the area occupied by the population Immigration and Emigration are referred to as Migration BASIC POPULATION PARAMETERS Population parameters affect population density HOW TO ESTIMATE POPULATION DENSITY? Techniques differ between organisms such that the technique to estimate deer cannot be applied to bacteria or protozoa or vice versa There are 2 fundamental attributes that affect the ecologists choice of technique for population estimation  WHY THE NEED TO ESTIMATE POPULATION DENSITY? Estimates of population are made for two reasons: 1. How to quantify nature – ecologist role 2. Estimates allow comparisons between different populations in terms of space and time measure 2 BROAD APPROACHES FOR POPULATION DENSITY ESTIMATION Absolute Density Number of individual per area/ per volume important for conservation and management Relative Density Comparative number of organisms; two areas of equal sizes, which area has more organism e.g, between area x and y; area x has more organism than area y ABSOLUTE DENSITY Making total counts and by using sampling methods Total counts - direct counting of populations - human population census, - trees in a given area, - breeding colonies can be photographed then later counted, - in general total counts are possible for few animals MEASUREMENTS OF ABSOLUTE DENSITY Sampling methods - to count only a small proportion of the population (sample) Using the sample to estimate the total population 2 general sampling techniques: 1) Use of quadrats 2) Capture-recapture method MEASUREMENTS OF ABSOLUTE DENSITY A. Quadrat Sampling - Count all individuals on several quadrats of known size, then extrapolate the average count to the whole area Requirements for using QS: the population in the quadrat must be determined exactly area of the quadrat must be known quadrat/s must be representative of the area achieved by random sampling  QUADRAT SAMPLING IN PLANT POPULATION Lay a transect in the upland hardwood forest 110 meters 3 transect line, 110 meters long, count all trees taller than 25cm within 1meter of each line By utilizing the quadrat method sampling for 1m distance old trees and seedlings, we can determine if (count tress taller than 25cm) populations were likely to change over time QUADRAT SAMPLING IN PLANT POPULATION Area of the quadrat must be known Size depends on what type of organisms you are taking samples Ex. 1x1 quadrat for grassland and seagrass 5x5 for saplings or seedlings 10x10 for mature trees However, you can modify your approach depending on the area and organism QS is highly used on plant sampling and slow-moving animals (gastropods) MEASUREMENTS OF ABSOLUTE DENSITY B. Capture-recapture method Capture, marking, release, and recapture-important for mobile animals Why? It allows not only an estimate of density but also estimates of birth rate and death rate for the population being studied Capture animal, mark (tag) them and then release them MEASUREMENTS OF ABSOLUTE DENSITY Peterson method: - Involves 2 sampling periods - Capture, mark and release at time 1 - Capture and check for marked animals at time 2 Time intervals between the 2 samples must be short because this method assumes a closed population with no recruitment of new individuals into the population between time 1 and 2 and no losses of marked individuals MEASUREMENTS OF ABSOLUTE DENSITY Formula for Capture-recapture method MEASUREMENTS OF ABSOLUTE DENSITY Example of Capture-recapture method Peter marked trout in small Norwegian lakes to estimate the size of the population that was subject to fishing. He marked and released 109 trout, and in 2nd sample a few days later caught 177 trout, of which 57 were marked. From the data, what is the estimate population size? MEASUREMENTS OF RELATIVE DENSITY Traps no caught per day per trap – animals caught will depend on their density, activity and range of movement, skill in placing traps – rough idea of abundance – night flying insects, pitfall traps for beetles, suction traps for aerial insects Pelt records trapper records dates back 300 years – of lynx MEASUREMENTS OF RELATIVE DENSITY Fecal pellets rabbits, deer, field mice – provides an index of pop size Vocalization frequency bird calls per 10 mins, can be used for frogs, cicadas, crickets Catch per unit effort index of fish abundance – no of fish per cast net or no of fish per 1 hour trawling MEASUREMENTS OF RELATIVE DENSITY Number of artifacts thing left behind – pupal cases of emerging insects Questionnaires to sportsmen (e.g.fish)and trappers Cover % ground surface covered – in botany, invertebrate studies of the rocky intertidal zone MEASUREMENTS OF RELATIVE DENSITY Feeding capacity bait taken – for rats and mice – index of density Roadside counts birds observed while driving standard distances NATALITY The production of new individuals by birth, hatching, germination or fission 2 aspects of reproduction must be distinguished: Fecundity Fertility NATALITY Fecundity - physiological notion that refers to an organism’s potential reproductive capacity Fertility - ecological concept based on the number of viable offspring produced during a period time NATALITY Realized Fertility rate for a human population may be only 1 birth per 15 years per female in the child-bearing ages Potential Fecundity rate for humans is 1 birth per 10 to 11 months per female in the childbearing ages Realized Fertility and Potential Fecundity MORTALITY Longevity - the age of death of individuals in a population 2 types: – Potential longevity – Realized longevity MORTALITY Potential longevity The maximum life span of an individual of a particular species is a limit set by the physiology of the organism, such that it simply dies of old age The average longevity of individuals living under optimum conditions However, organisms rarely live under optimum conditions-most die from disease, or eaten by predators or succumb to a number of natural hazards MORTALITY Realized longevity The actual life span of an organism Can be measured in the field, while potential longevity only in labs or zoos Example: European robin has an average life expectation of 1 year in the wild, whereas it can live at least 11 year in captivity POPULATION DISPERSION PATTERN Dispersion Pattern the spatial relationship between members of a population within a habitat, often characteristic of a particular species Patterns are often characteristic of a particular species; they depend on local environmental conditions and the species’ growth characteristics (as for plants) or behavior (as for animals).  TYPES OF DISPERSION PATTERN A population may have a uniform, random, or clumped distribution. Territorial birds, such as penguins, tend to have uniform distribution. Plants with wind-dispersed seeds, such as dandelions, are usually distributed randomly. Animals, such as elephants, that travel in groups exhibit clumped distribution. TYPES OF DISPERSION PATTERN Random Organisms have an unpredictable distribution. It usually occurs because members of a species do not frequently interact with one another or are not heavily influenced by the microenvironments within their habitat. The least common pattern of distribution found in populations TYPES OF DISPERSION PATTERN Uniform members of the population maintain a minimum distance from one another, generally indicates strong intraspecific competition In plant populations, this could result from competition for water, sunlight, or available nutrients, while among animals, even spacing indicates strong territoriality. TYPES OF DISPERSION PATTERN Clumped The most frequent pattern of distribution in a population Individuals are clustered together in groups in response to uneven distribution of resources, tendency of offspring to remain with parents, or some type of social order. May be linked with defense (safety in numbers) or mating behavior. In plants, soil type, availability of water or the manner in which the plant reproduces may favor clumped distribution patterns.