Population Dynamics – Population Ecology

1. Population Dynamics – Population Ecology Chapter 14

2. Characteristics of Populations – 14.1 • How can we determine… • …population sizes for each individual species? • …what individual population size is ideal for a particular habitat? • …when a population reaches its ideal size?

3. Population Size and Density • Population Size the number of individuals of a specific species occupying a given area/volume at a given time • Population Density (D)  the number of individuals of the same species that occur per unit area or volume. Calculated by dividing the total number counted (N) by the space (S) • Crude Density population density measured in terms of number of organisms of the same species within the TOTAL AREA OR VOLUME • Ecological Density population density measured in terms of the number of individuals of the same species per unit area or volume ACTUALLY USED BY THE INDIVIDUALS.

5. Population Size and Density • Dispersion (p.652, fig. 4) • Clumped  individuals in a population are more concentrated in certain parts of a habitat • Uniform  individuals in a population are equally spaced throughout a habitat • Random  individuals in a population are spread in an unpredictable and patternless manner.

7. Measuring Population Characteristics • Hard to accurately measure every single organism in a given habitat so sampling is completed. • Quadrat a sampling frame used for estimating population size; frames can be real or virtual. Count numbers in random quadrats and then extrapolate population size estimations to a given area. Best for a stationary species.

8. Mark-Recapture Sampling • Moving populations pose a problem as do populations that demonstrate clumped dispersion. • Mark-recapture method sampling technique for estimating population size and density by comparing the proportion of marked and unmarked animals captured in a given area. • Marking must not interfere with the individual and must not allow it to be recaptured more easily. • Every individual in a population must have an equal opportunity of being captured. • The population size does not increase or decrease so the proportion of marked to unmarked does not change. Total number marked (M) = # of recaptures (m) Total population (N) size of second sample (n)

10. Mark-Recapture Sampling • Tracking Populations • Migratory patterns or behaviour patterns • Collars, tags, monitors using satellite linked GIS (geographic information systems) and GPS (geographic positioning system) technology • GPS tells you that you are at point X,Y,Z while GIS tells you that X,Y,Z is an oak tree, or a spot in a stream with a pH level of 5.4. GPS tells us the "where". GIS tells us the "what". • Ethics should we be doing this to aid with reducing effects due to environmental change and determining if these effects are human centred or occurring naturally? • CCAC  Canadian Council on Animal Care • Three Rs: • Reduction – use of animals • Refinement – of techniques with animals • Replace – trapping with computer simulations

11. Measuring and Modeling Population Change – 14.2 • Carrying Capacity the maximum number of organisms that can be sustained by available resources over a given period of time. Determined by biotic and abiotic factors. Factors Affecting Growth • Population Dynamics changes in a population determined by natality, mortality, immigration and emigration. • Fecundity  plays into population dynamics in that it is the potential for a species to produce offspring in one lifetime. Starfish = 1 million eggs per year for 15 years, hippo = 20 young over lifetime of 45 years. • Fertility (# of offspring actually produced in a lifetime, is usually significantly less than fecundity. WHY?

13. Measuring and Modeling Population Change • Survivorship • Type 1  low mortality rates until they are beyond their reproductive years, slow sexual maturity, few offspring • Type 3  high mortality rates when young and those that do age have a greatly reduced mortality rate; large offspring numbers, few live.

14. Calculating Changes in Population Size • Population change = [(b + i) – (d + e)] x 100 • Initial population size (n) • Open vs. Closed Population • Open = migration, natality and mortality are all involved • Closed = natality and mortality are involved (islands) • Biotic Potential  the maximum rate a population can increase under ideal conditions.

15. Population Growth Models • Geometric Growth a pattern of population growth where organisms reproduce at fixed intervals as a constant rate. λ(t) = N(t + 1)N = population size N(t) (t + 1) = year in question (t) = original year λ = fixed growth rate N (t) = N(0)λt N(0) = initial population size N (t) = population size at t years

17. Population Growth Models • Exponential Growth a pattern of population growth where organisms reproduce continuously at a constant rate. dN = rN r = (per capita birth rate – per dt capita death rate) • dN/ dt = instantaneous growth rate of the population and N is the population size • More useful is td = 0.69td = doubling time r

19. Modeling Logistic Growth • Geometric and Exponential growth assume growth at the same rate indefinitely. Why is this not true? • Logistic Growth  model of population growth that levels off as the size of the population approaches its carrying capacity. It is the most common pattern of growth seen in nature. dN = rmaxN[(K-N)]rmax= maximum intrinsic growth rate dt K dN/ dt = growth rate of the population at a given time N = the population size at a given time K = carrying capacity of the environment • Note that if N nears K then the relationship will near 0.

20. Modeling Logistic Growth • Lag phase small population size and growth just starting out • Log phase rapid population growth, characteristic of geometic and exponential growth • Stationary phase population growth decreases and population size reaches carrying capacity. At this point the population is said to be in dynamic equilibrium (births = deaths)

22. Factors Affecting Population Change – 14.3 • Carrying Capacity Factors • Materials and E amount of usable E from sun, as well as water, carbon and other essential nutrients • Density only so many organisms can live in an area at one time • Density dependent factors : Intraspecific competition, Predation, Disease • IntraspecificCompetition – same species competing • Can have impact on fecundity (p. 671, fig. 2) – bears • Predation – the more of a species population, the more easily predated (e.g. moose and wolves) • Disease – Mycoplasmagallisepticumand the house finch

23. Factors Affecting Population Change • Allee effect – when a population fails to reproduce enough to offset mortality when the population is low; such populations do not normally survive. • Minimal viable population size – smallest number of individuals that ensures that a population can persist for a determined interval of time. • Density independent factors – fire, flood, extreme weather • Limiting factors – limit populations from achieving their biotic potential

24. Interactions Within Communities – 14.4 • Community all populations in a given ecosystem at a given time. Interactions are inevitable. • Ecological Niches • Ecological niche – an organism’s biological characteristics, including use of and interaction with abiotic and biotic resources in its environment. • Habitat is an organism’s “address” and ecological niche is its “occupation”.

25. Interactions Within Communities • Fundamental Niche biological characteristics of the organism and the set of resources individuals in the population are theoretically capable of using under ideal conditions. • Realized Niche biological characteristics of the organism and the resources individuals in the population actually use due to current environmental conditions. • A fundamental niche may not be realized due to interspecific competition therefore the organism is living in a realized niche

26. Interspecific Competition • Interactions between species can be categorized 5 ways. (p.677, table 1)

27. Interspecific Competition •  aggression between individuals of different species who fight over the same resources • Interference competition is the actual fighting over resources • Exploitative competition is the consumption or use of shared resources Ways to cope: • Population size of the weaker competitor could decrease • Change in behaviour to use different resources • Migration Ultimately the organisms want competition to decline • Resource partitioning avoidance of, or reduction in, competition for similar resources by individuals of different species occupying different non-overlapping ecological niches. Direct reasoning behind evolution.

28. Interspecific Competition - Gause – 1934, Principle of Competitive Exclusion - Exploitative competition Resource partitioning

29. Predation – predator-prey relationship • In some cases there is a steady level which is achieved and the relationship between predator and prey is allowed to coexist naturally. There can also be oscillations between predator and prey being more abundant as well as natural cycling between the two based on environmental conditions or natural reproduction. Lynx (blue) & Hare (red)

30. Defense Mechanisms • Active – avoidance of predators requiring energy to be expended. May involve fleeing and mobbing • Passive - avoidance of predators not requiring excess energy to be expended. • Physical there are many different types of physical changes that can be utilized: • Aggressive – thorns, hooks, spines & needles can be used by plants • Passive – camouflage, visual warnings of poison

31. Defense Mechanisms • Batesianmimicry  palatable species mimics an unpalatable one • Mullerian mimicry  several unrelated but protected animal species that resemble one another and as such allowed predators to learn quickly to avoid such species as all are unpalatable. • Chemical  oils created by plant (or animal) that smell poor and are distasteful Bombardier beetle

32. Symbiosis “living together” • Mutualism = both species in the relationship benefit and neither is harmed. • Obligatory mutualismrelationship in which neither species involved could survive without the other. • Commensalism = one organism benefits and the other organism is unaffected. There is some debate about whether this classification truly exists.

33. Symbiosis “living together” • Parasitism = one organism (the parasite) benefits at the expense of another (the host) which is usually harmed but not killed. • Microparasites = too small to see with naked eye. Plasmodia • Macroparasites = easily visible. Tapeworms, fleas, ticks. • Endoparasites = live and feed within the host’s body. • Ectoparasites = live and feed on the outside of the host. Lice, ticks, mites. • Social parasites = complete their life cycle by manipulating the social behaviour of their hosts. North American cowbird  utilizes nests of other birds and their eggs hatch first.

34. Distribution of Community Equilibrium • Populations do not normally exceed the resources necessary for survival, that is, they do not exceed the environment’s carrying capacity. • Natural disasters can alter populations within a community and break down intricate interactions. • Exotic or non-indigenous species can also disrupt ecosystems to such an extent that they pose a serious threat to the habitats they invade.

35. Sociobiology • Study of the biological basis of social behavior of animals in societies • Costs and Benefits to Social Behaviour • Benefits • Reduction in predator pressure by improved detection or repulsion of enemies • Improved foraging efficiency • Improved defenses of limited resources • Improved care of offspring through communal feeding and protection

36. Sociobiology • Costs • Increased competition with the group (food, mates, nest sites, materials, resources) • Increased risk of infection (disease, parasites) • Increased risk of exploitation of parental care by conspecfics • Increased risk that conspecifics will kill one’s progeny

37. Sociobiology • Altruism • Self-sacrificing behavior that is not limited to humans by any means. In many species it is an important aspect of cooperation. • One of the most important aspects of altruism concerns assisting another individual in reproducing. • A misconception about altruism is that the individual is sacrificing itself for the group or the species however the problem is that the behavior is never going to be passed on, as offspring will not be left.

38. Sociobiology • Kin Selection • Evolution will favor any strategy that increases the net flow of a combination of genes to the next generation • Selection acting to favor the propagation of genes by directing altruism towards relatives is known as kin selection

39. Sociobiology • Kin Selection • Inclusive fitness = sum of genes propagated by personal reproduction and by the effect of help with relatives’ reproduction • Coefficient of Relatedness • Full sibling or parent to offspring = 0.5 • Half sibling, uncle/aunt to niece/nephew or grandparent to grandchild = 0.25 • Cousin to cousin = 0.125

40. Sociobiology • Reciprocity • Individuals may form partnerships in which altruistic acts are exchanged • They must share no genes to make it true • Cheating should not occur if the cost of not reciprocating exceeds the benefits of receiving future aid

41. Sociobiology • Vertebrate Societies • In comparison to insect societies vertebrates form far less organized groups • paradox = we have larger brains and therein should be capable of more complex behavior • lower amount of gene sharing though • more conflict • Cooperative Breeding • “Helpers” are fully capable of breeding but remain as non-reproductive altruists • Situation resembles that of a family and is explained by inclusive fitness concept

42. Sociobiology • Nepotism – favoring relatives • Alarm Calling • Females are more likely than males to give the alarm call. • Females tend to live with related females • The inclusive fitness gained by keeping offspring alive is no different from the inclusive fitness gained by saving the lives of assorted nondescendant kin. Belding Ground Squirrel

43. Sociobiology • Certain individuals, in some social groups, will exhibit behavior that will benefit the group over the individual itself • Pied kingfisher • Primary helper, secondary helper and delayers