Populations

1. Populations Dr. Stafford 2018

2. How Populations Grow • Ways to describe a population • Geographic range – the places a population lives • Can vary depending on the species • Very small for bacteria • Very large for a predator • Historic vs present range • Useful in determining its interactions with other species

3. How Populations Grow • Ways to describe a population (cont.) • Growth rate – will the population grow or decrease? • Hunting can cause the growth rate to decrease • Introduction in a new area usually leads to an increase in growth rate

4. How Populations Grow • Ways to describe a population (cont.) • Density and distribution • Population density is the number of individuals in a unit area • Different species can have very different densities even within the same are • Densities can change due to species changes

6. How Populations Grow • Ways to describe a population (cont.) • Density and distribution • Distribution – describes the way the individuals are spaced out • Random – location independent on other individuals • Clumped – most common – help avoid predators – social considerations • Uniform – due to competition for resources

7. Fig. 53-4 (a) Clumped (b) Uniform (c) Random

8. How Populations Grow • Ways to describe a population (cont.) • Age structure • How many of each age • How many of each sex • Usually only the females can reproduce • Usually they only reproduce in a certain age range

10. Population Growth • Things that can cause an increase in population size – birth rate and immigration • Things that can cause a decrease in population size – death rate and emigration

11. Population Growth • Birth rate and death rate • Birth rate – number of individuals born in a given time • Death rate – number of individuals that die in a given time • If birth rate is higher than death rate the population will grow • If death rate is higher than birth rate, the population will decrease • If death rate and birth rate are equal, the population will stay constant

12. Population Growth • Immigration and emigration • Immigration is when individuals move into an area from another are • Emigration is when individuals move out of an area • Depends on how far they travel, how quickly they move, and whether human activity moves them around • Could be because of a food shortage or young moving to find new mates

13. Population Growth • Exponential growth – the larger a population gets the faster it will grow – due to introduction into a new area - results in a J-curve • Due to unlimited resources and space • Organisms that reproduce rapidly like bacteria – every 20 minutes • 23 after 20 minutes and 26 after 40 minutes and 29 after 60 minutes • Slow reproducing organisms – elephants – if all elephants lived the whole time – 20 million elephants in 750 years

15. Population Growth • Logistic growth – growth with limits – no organism can grow exponentially forever – growth slows and then stops – makes an S-curve graph • Phases of growth • Phase 1 – exponential growth – no limits • Phase 2 – still increases, but at a slower rate due to limits • Phase 3 – growth stops and the population size levels off – may have an increase in death rate

17. Population Growth • Carrying capacity – maximum number of individuals of a particular species that a particular environment can support • Results in a jagged, horizontal line on the growth curve • A result of several abiotic and biotic factors in the environment • Can be affected by the seasons • Hunting and fishing limits

19. Limits to Growth • Limiting Factors – any factor that controls the growth of a population • Can be abiotic or biotic factors • Can be influenced by the population density • Should keep the population size between extinction and overrunning the ecosystem • Involved in evolution – they determine who survives and reproduces

20. Limits to Growth • Density-dependent limiting factors – when they are affected by the number of individuals in a certain area • Competition – competing for a certain resource – the more individuals the quicker they use up the resources • Could be intraspecific or interspecific • Major force behind evolution

21. Limits to Growth • Density-dependent factors (cont.) • Parasitism and disease – parasites and disease causing organisms spread quicker in a dense population

22. Limits to Growth • Density-dependent factors (cont.) • Stress from overcrowding • Causes fighting which can lead to death or more susceptibility to disease • Can cause females to eat their young • Can lower the birth rate • Can increase emigration

23. Limits to Growth • Density-dependent factors (cont.) • Predator-prey relationships – an increase or decrease in either the predator or prey will affect the population size of the other • Herbivore effects – similar to predator-prey relationships – can be affected by the weather • Humans as predators • Hunting and fishing

25. Limits to Growth • Density-independent factors – affect all populations regardless of size or density • Can lead to a crash from which they may or may not recover • Usually due to a weather related disaster • Control of introduced species • Still somewhat affected by density and size

26. Limits to Growth • If carrying capacity falls low enough, populations can be wiped out, leading to species extinction • Some factors such as rainfall and temperature can vary. • Sometimes human activity divides areas limiting the carrying capacity for each of the smaller areas

27. Human Population Growth • Varies depending on the countries • Developed countries like the U. S. has a slower growth • Still a very fast growth in underdeveloped countries • The population growth for humans has varied • Slow growth for most of human existence • Exponential growth for the last hundred plus years

29. Human Population Growth • Exponential growth due to several factors • More reliable food supply • Better sanitation • Improved nutrition • Better medical care

30. Human Population Growth • Thomas Malthus in early 1800’s predicted the human population cannot grow exponentially forever • Predicted war which is competition would decrease it • Famine which is limited resources • Disease which is a density-dependent factor that controls population growth

31. Human Population Growth • Population growth rate increased until about 1959 and the increase rate has been gradually slowing since then. However, the population is still growing.

32. Human Population Growth • Demography – the study of human populations – attempts to explain how populations will change over time • Birth rates • Death rates • Age structure

34. Human Population Growth • Demographic transition • Stage 1 –birth rate and death rate both high – population is stable • Stage 2 – birth rate stays high and death rate drops – population grows rapidly • Stage 3 - both birth and death rate are low – population is steady • Most of the population growth is attributed to ten countries in India, China, and sub-Saharan Africa

35. Human Population Growth • Age structure diagrams – compare the number of people in different age groups and different sexes. • If more people are young the population will grow • If more people are old, the population will decrease • If people are equally distributed age-wise, the population will be steady • Current projections say that by 2050 the population will be 9 billion.

36. Humans and Global Change • Changing atmosphere and climate • Carbon dioxide levels in the atmosphere have been rising since the industrial revolution. • Most of the carbon dioxide (greenhouse gas) • Most is from burning fossil fuels • Worry about climate change and global warming • Could cause movement of organisms and maybe even extinction

38. Humans and Global Change • Acid rain – burning of fossil fuels that results in release of nitrous oxide and sulfur dioxide • Damages leaves and roots of plants • Acidifies water and can kill fish • Acidifies soil and interferes with bacterial decay • Ocean acidification- due to high levels of carbon dioxide

39. Humans and Global Change • Agriculture practices such as cattle farming and rice farming release methane gas (greenhouse gas) • Changes in land use for human use – 3/4 of the land has already been modified • Deforestation – results in decrease in water quality in streams and soil erosion on hills – renewable resource

40. Humans and Global Change • Habitat loss – leading cause of extinction • Habitat fragmentation- the smaller the land fragment the fewer the number of species that live there – makes it more vulnerable due to loss of biodiversity • Hunting and fishing • Invasive species – will affect native species

41. Humans and Global Change • Pollution – CFC’s – used as a refrigerant and in aerosol cans – destroys the ozone layer – results in more harmful UV sunlight • Ground-level ozone from cars and industries - smog

42. Humans and Global Change • Biological magnification – the pollutant will concentrate as you go up a food chain or food web. • DDT is a prime example of this – it goes from fish to sea birds and results in soft egg shells that will break on laying • PCB’s – now outlawed but still persists • Heavy metals – cadmium, lead, mercury, and zinc – will accumulate in a food web – unleaded gasoline

43. Ecological Succession • Ecological succession – changes an ecosytem goes through after changes occur • Primary succession – occurs on rock where no previous ecosystem existed – no soil • Pioneer species – the first organism to grow – lichen is usually the first – symbiotic fungus, yeast, and photosynthetic organism

45. Ecological Succession • Secondary succession – a disturbance to an existing community – much faster than primary succession • Often due to forest fires and logging