Population Ecology NRM

Transcription

1 Population Ecology NRM

2 What do we need?

3 MAKING DECISIONS Consensus working through views until agreement among all CONSENSUS Informed analyze options through respectful discussion INFORMED DECISION Majority voting by those who have authority to vote SIMPLE MAJORITY Imposed decision by one with authority AGREEMENT IMPOSED

4 Levels of organization from genes to ecosystems Biosphere Ecosystems Communities Populations Organisms Organs Tissues Cells Genes ECOLOGY ORGAN SYSTEM LEVEL Nervous system ECOSYSTEM LEVEL Singharaja forest COMMUNITY LEVEL All organisms in Singharaja forest POPULATION LEVEL Group of flying foxes ORGANISM LEVEL Flying fox ORGAN LEVEL Brain CELLULAR LEVEL Nerve cell MOLECULAR LEVEL Molecule of DNA Genes Brain Nerve TISSUE LEVEL Nervous tissue Spinal cord

5 Levels of Organization Individual- one organism (living) Ex a sambar Population- groups of individuals that belong to the species and live in the same area (defined area) (living-living same species) and usually isolated to some degree from other similar groups Ex many sambar

6 Wildlife Management Population Ecology is the study of the factors that affect the population levels, survival, and reproduction of individual species in a specific area. A population is the number of individuals of a species in one area at one time. Wildlife management is the application of scientific knowledge and technical skills to protect, preserve, conserve, limit, enhance, or extend the value of wildlife and its habitat Wildlife are any non-domesticated vertebrate animals, including birds, mammals, reptiles, and amphibians

7 Population Characteristics 1. Population Density: The number of organisms per unit area 2. Spatial Distribution: Dispersion: The pattern of spacing a population within an area 3 main types of dispersion Clumped Uniform Random The primary cause of dispersion is resource availability

8 Population Limiting Factors 3. Population growth rate How fast a given population grows Factors that influence this are: Natality ( Birth rate) Mortality ( Death rate) Emigration (the number of individuals moving away from a population) Immigration (the number of individuals moving toa population)

9 Population Limiting Factors Density-independent factors Factors that limit population size, regardless of population density. These are usually abiotic factors They include natural phenomena, such as weather events Drought, flooding, extreme heat or cold, tornadoes, hurricanes, fires, etc.

10 Population Limiting Factors Density-dependent factors Any factor in the environment that depends on the number of members in a population per unit area Usually biotic factors These include Predation Disease Parasites Competition

11 Population Limiting Factors Population growth models Limits to exponential growth Population Density (the number of individuals per unit of land area or water volume) increases as well Competition follows as nutrients and resources are used up The limit to population size that a particular environment can support is called carrying capacity (k)

12 What population do you think this is?

13 Human Population Growth Curve

14 World rice yield (t/ha) Annual rate of yield increase: 52 kg grain/ha (R 2 =0.98) Semi-dwarf, short duration MV Yield potential Dwarfism Short duration Grain dormancy IR8 Irrigation 2-3 crops/year N fertilizer Pesticides Resistance to insects & diseases Adverse soil tolerance Mechanized tillage Direct seeding Herbicides IPM More N & P fertilizer Decline in manure and green manure Mechanized harvest Grain quality, Hybrid rice Floodprone rice Rainfed rice Abiotic stresses Wide hybridization New Plant Type Isogenic lines/mas Gene pyramiding IR26 IR36 IR64 IR72 PSBRc18 Diversification Reduced tillage Dry-seeding Water-saving irrigation Site-specific NM Post-harvest technologies Community IPM Ecosystem services Yield potential Gene discovery Precision breeding: - abiotic stresses - biotic stresses - adaptation to CA - biofortification - grain quality NSIC Rc

15 Trends of Rice Extent, Annual Production, Average Yield, Rice Imports and Population Growth over past Six decades ( ) in Sri Lanka Decade Population (millions) Production (ton. millions) Asweddumize d Extent (ha. millions) Yield (t./ha) National Average Rice Imports as a % of Requirement <1 Year <1 Increase over 1940 decade 3.36 fold fold 1.84 fold 6.47 fold Source : Central Bank Report

16 So, what do you think is going to happen to the human population? We will probably reach our carrying capacity. Our growth rate will start to look like most organisms, which is the Logistic Growth Model Carrying Capacity (k)

17 Population Limiting Factors Population growth models Logistic Growth Model Often called the S-shaped growth curve Occurs when a population s growth slows or stops following exponential growth. Growth stops at the population s carrying capacity Populations stop increasing when: Birth rate is less than death rate (Birth rate < Death rate) Emigration exceeds Immigration (Emigration > Immigration)

18 Population Limiting Factors Population growth models Logistic Growth Model The S-curve is not as pretty as the image looks 1. Carrying capacity can be raised or lowered. How? Example 1: Artificial fertilizers have raised k Example 2: Decreased habitat can lower k 2. Populations don not reach k as smoothly as in the logistic graph. Boom-and-Bust Cycles Predator-Prey Cycles

19 Determining the Size of a Population Most population sizes are estimates It is impossible for ecologists and managers to count every single species of wildlife. Most biologists use mathematical formulas to estimate the size of a population rather than count each individual. The Mark-Recapture Method is the most widely used approach. Mark-Recapture involves trapping and marking individuals of a species. These individuals are then released and traps are re-set. The proportion of the newly caught individuals is used to determine the overall size of a population.

20 Example For example, let s imagine we are counting pigeon populations in the Kandy area. We set traps and catch 12 birds, which we then tag. These birds are released, and several weeks later we re-set the same traps. On the second try we catch 12 birds. Of the 12 birds, 4 have been previously tagged. This means that for this area, 4 out of 12, or 1/3 are tagged. If 1/3 are tagged, and we tagged 12 total, that would mean that 12 is 1/3 of the total population for this area. If we multiply 12 times 3, we had get the total estimated population: 36 pigeons for the Kandy area.

21 Mark Recapture Equation The Mark-Recapture Equation: If N = the total population of individuals of a species in a given area, then N = [1st catch] x [2nd catch] / [number caught twice] For example, in our pigeon example We caught 12 the first time. We caught 12 the second time. We re-caught 4 the second time. N = (12 x 12) / 4 N = 144/4 = 36 N = 36

22 Fecundity & Fertility In Population Ecology, two terms serve as a basis for the ability to maintain a population of a species. Fecundity the maximum reproductive ability of a breeding female of a species E.g. deer can have 2-3 fawns per year max Human females have had over 40 children Fertility the actual reproductive performance of a breeding female of a species E.g. most deers does have 1 fawn per year Most human females have 1-2 children if they have any

23 Factors that Naturally Limit Population Growth In nature, no species ever reaches its full reproductive potential (fecundity) Direct killing and limits to reproduction inhibit population growth Genes do not code for natural population limits a species cannot genetically self-regulate its population levels With unrestricted access to resources, populations increase indefinitely Factors outside of a species genes must limit the growth and reproduction of a species population.

24 Fecundity & Fertility With unlimited access to resources and no population limits, a species population will increase without limit.

25 Natural Limiting Factors If a game manager s goal is to increase the size of Wisconsin s deer herd, simply reducing hunting of a species is not enough. A population ecologist or game manager must take into consideration the impact of natural limits to population growth as well as fertility and fecundity These factors include Resource Consumption (food, water) & predation Breeding/nesting (cover) Habitat suitability (lack of pollution, invasive species, fragmentation) Availability of Mates Emigration and Immigration (individuals leaving, individuals coming) If game managers need to change a species population, they must use one or more of these factors. All must be taken into consideration in any game management decision.

26 Carrying Capacities A game manager must also consider what is too many of an animal for a particular habitat. Every habitat has a maximum carrying capacity for each species. The Carrying Capacity, or K-value, represents the maximum number of individuals of a species that a habitat can sustainably maintain. Note: a Carrying Capacity is not a fixed number it will change each year based on weather, competition from other species, and availability of resources. Most K-values naturally fluctuate from year depending on the availability of resources.

27 Carrying Capacity The maximum population size that can be sustained by an environment

28 Weakness of CC in NRM Finding a single ecological carrying capacity that accommodates ecological, social and managerial demands

29 General Dimensions of Carrying Capacity Ecological Societal Managerial

30 Fecundity & Fertility With unlimited access to resources and no population limits, a species population will increase without limit.

31 K-values and Saturation Points A species can temporarily surpass its carrying capacity, but not for a long period of time If it does surpass its carrying capacity, its population will crash if not reduced due to a shortage of resources. If a species reaches the K-value for its habitat (the carrying capacity), this is known as the Saturation Point. The habitat is saturated with individuals of that species and has as many as it can sustain.

32 Dispersal Patterns Carrying Capacities, or K-values, are more like abstract ideas rather than concrete numbers. You will not find a specific maximum number for a habitat, only a general idea of what would be an unsustainable population. K-values can also be affected by the dispersal patterns of a species. Wildlife rarely have uniform dispersal Their type of dispersal can create unequal pressures on the resources of a particular habitat. For example, one part of a habitat may be over its K-value while another part of the same habitat may be under. For example, deer are managed in state units rather than as an entire state herd for this reason.

33 Age Dispersal Patterns Species can have spatial dispersion across a habitat (clumped, uniform, or random) A species can also have age-dispersal patterns The investigation of changes in a species population due to age is also major a part of population ecology. This information can then be graphed to create a survivorship curve. A survivorship curve represents the numbers of a species that are alive at each stage of life.

34 Survivorship Curves

35 Survivorship Curves A survivorship can fall into one of three categories. Type I on the survivorship curve starts off relatively flat and then drops off steeply at an older age. Death rates are relatively low until later in life when old age claims most individuals. The death rate for Type I species is highest at old age. These species tend to produce few young, as they are less likely to die due to good care. Type II is the intermediate category, with a steady even death rate over the course of a species expected lifespan. The risk of death is fairly consistent over the individual s lifespan Type III curves drop off steeply immediately, representing high infant mortality, but then levels off for adults. This type of curve is affiliated with species that produce large numbers of young with the expectation that few of them will make it to maturity. Fish and frogs lay large numbers of eggs with only a small percentage making it to adulthood. Plants often tend to be good examples, producing many seeds, few of which become adults.

36 Regulating Populations Regulating a species population is incredibly complex because of the intense interaction of factors. A game manager must take into account Resource Consumption (food, water) & predation Breeding/nesting (cover) Habitat suitability (lack of pollution, invasive species, and fragmentation) Availability of Mates (e.g. Earn of Buck vs. Earn a Doe) Emigration and Immigration (individuals leaving, individuals coming) Carrying Capacity of a Habitat Average age of a species and its survivorship curve Dispersion of a species and their resources Bottom line a population is not just a number, but a collection of highly varying factors and inputs. Question, we need to understand how could each of these factors increase and decrease the population of a species in a particular habitat?