P OPULATION E COLOGY Slide 2 W ILDLIFE M ANAGEMENT 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 Slide 3 D ETERMINING THE S IZE OF A P OPULATION 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. Slide 4 E XAMPLE For example, lets imagine we are counting pheasant populations in the Waterford 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, wed get the total estimated population: 36 pheasants for the Waterford area. Slide 5 M ARK R ECAPTURE E QUATION 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 pheasant 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 Slide 6 F ECUNDITY & F ERTILITY 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. whitetail 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 whitetail does have 1 fawn per year Most human females have 1-2 children if they have any Slide 7 F ACTORS THAT N ATURALLY L IMIT P OPULATION G ROWTH In nature, no species ever reaches its full reproductive potential (fecundity) This is because of natural population limits such as predation, competition, and disease. Genes do not code for natural population limits A species cannot genetically limit its own population levels With unrestricted access to resources, populations increase without limit. Factors outside of a species genes must limit the growth and reproduction of a species population. Slide 8 C ARRYING C APACITIES 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 and from place to place depending on the availability of resources. Slide 9 F ECUNDITY & F ERTILITY As species increase their population, their performance in their habitat can change their physical attributes. This can have a significant impact on game management practices. High game densities may at first seem ideal, especially to hunters. However, dense game populations can Reduce birthrates Reduce individual size of game Increase the spread of disease Source: http://www.cals.ncsu.edu/course/fw353/Estimate.htmhttp://www.cals.ncsu.edu/course/fw353/Estimate.htm Slide 10 K- VALUES AND S ATURATION P OINTS 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. Exceeding the saturation point of a habitat can quickly drive other species in that habitat to extinction locally. Slide 11 W ISCONSIN D EER D ISPERSION ( DNR. GOV ) Game population estimates may be expressed in terms of abundance or density. Abundance estimates are the total number of individuals estimated for an entire unit. Density can be calculated by dividing the abundance estimate by the area (square miles) within the unit. Density estimates are useful for comparing population estimates among deer management units. The amount of game per unit area matters more than the total amount of game. For example 40 deer is a lot for one small forest but not a lot for an entire county! Slide 12 D ISPERSAL P ATTERNS OF W ILDLIFE Deer and other game never disperse themselves evenly. This means that dividing total population of an animal by the total land area will give you a density that is too low. 3 dispersal patterns include Clumped: when individuals of a species are more likely to be together in groups ( most common ) Uniform: when individuals of a species are more likely to equally distanced from each other (rare ). Random: when the arrangement of a species follows no pattern and is not predictable. Slide 13 D ENSITIES AND C ARRY C APACITIES Density is more than just deer per area. The habitat quality and amount in that area matters as much or more as the total number of deer in that area. Deer and other game do not disperse themselves evenly across a county or deer management unit. The level patchiness of their habitat affects the actual density of deer and other game. For example, if only 20% of a county is suitable habitat for deer, their density is 5x greater than the calculated density for an entire county or deer management area. This is because 80% of the area would be unusable to them. This means that even with a relatively low density for the county, if there is a perceived high population density for the deer it will result in smaller bucks, lower reproduction, and increased spread of disease. Deer densities will always be high if suitable habitat is low. Why? TPS What impact would this have on hunting? Slide 14 D ISPERSAL P ATTERNS 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. Deer are managed in state units rather than as an entire state herd for this reason. Slide 15 D EER A BUNDANCE M APS Here, this area looks like a better place to hunt. Slide 16 D EER D ENSITY M APS Here, this area looks like a better place to hunt Which area will have the bigger bucks? Slide 17 D EER A BUNDANCE AND D ENSITIES IN W ISCONSIN D EER M ANAGEMENT U NITS D EER A BUNDANCE AND D ENSITIES IN W ISCONSIN D EER M ANAGEMENT U NITS DNR. GOV Density estimates for deer management units are based largely on the number of antlered bucks harvested in the unit. The resulting density estimates are averages for the entire unit and may not accurately reflect local deer density. Density within a unit can vary greatly from habitat to habitat. There can be considerable local variation in density within deer management units due to differences in deer habitat quality and local hunting pressure. i.e. a well managed habitat will have a higher density of deer but can also allow for more reproduction and bigger bucks. i.e. a habitat with low hunting pressure will have a higher density but may also have smaller bucks and lower reproduction. Habitat management is critical for game management! Slide 18 A GE D ISPERSAL P ATTERNS 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. Slide 19 S URVIVORSHIP C URVES 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 individuals 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. Slide 20 S URVIVORSHIP C URVES Slide 21 R EGULATING P OPULATIONS 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 & Patchiness of 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. TPS how could each of these factors increase and decrease the population of a species in a particular habitat?