U.S.G.S. Let’s Eat!! Trophic levels

What do the First and Second Laws of Thermodynamics Tell us? First Law: Energy in = Energy Out Until humans: Energy =sit by fire, or in the sun Sun: 30% reflectd, 50% converted to heat, the rest goes to the water cycle, except <1% used by plants Second Law: No process is 100% efficient –Energy In = Work + Heat

What is Ecological Efficiency? Plants absorb how much sunlight? –1-3% Herbivores use how much of the plant energy? –10% Where does the rest go? –Heat and respiration What is the efficiency of a carnivore? –10% Example: Humans –0.02 x 0.1 x0.1 = , 2% of the solar energy that passed through the plant, cow, human

Species interaction tactics Unique niches Competition--competitive exclusion by specialization vs. extinction Specialization Symbiosis--commensalism, mutualism, parasitism Predation ==population ecology

Population Ecology 1. Density and Distribution 2. Growth a. Exponential b. Logistic 3. Life Histories 4. Population Limiting Factors 5. Human population growth (Modified from a WWW site that I have lost the reference to!

Examples of applications Invasive species Endangered species Pest control (e.g., agriculture) Human population growth

Density: the number of organisms in a unit area Distribution: how the organisms are spaced in the area Fig Population. Individuals of same species occupying same general area.

Changes in population size Growing Fig Fig Fluctuating Shrinking Fig Northern Pintail Duck

Questions Why do populations change in size? What factors determine rates of population growth or decline? How do these differ among species?

2. Population Growth a. exponential growth The change in population size (N) in an interval of time is number of births – number of deaths, or number of births – number of deaths, or ∆N = B - D ∆t (ignoring immigration and emigration) ∆t (ignoring immigration and emigration) If b (birth rate) is the number of offspring produced over a period of time by an average individual, and d (death rate) is the average number of deaths per individual, then ∆N = bN – dN or ∆N = (b – d)N ∆N = bN – dN or ∆N = (b – d)N ∆t ∆t ∆t ∆t

Population Growth: exponential growth The difference between the birth rate and the death rate is the per capita growth rate r = b - d The growth equation can be rewritten as ∆N = rNordN = rN ∆N = rNordN = rN ∆t dt ∆t dt Exponential growth occurs when resources are unlimited and the population is small (doesn’t happen often). The r is maximal (r max ) and it is called the intrinsic rate of increase.

Population Growth: exponential growth Fig Note that: 1.r is constant, but N grows faster as time goes on. 2.What happens with different r’s in terms of total numbers and time to reach those numbers?

r can also be negative (population decreasing) if r is zero, the population does not change in size thus, the rate of increase (or decrease) of a population can change over time.

Exponential growth does not happen often: Fig – Whooping crane

reindeer slide Reindeer on the Pribalof Islands, Bering Sea Or indefinitely:

2.b. Logistic growth Fig Most populations are limited in growth at some carrying capacity (K) (the maximum population size a habitat can accommodate)

Logistic Growth Equation: incorporates changes in growth rate as population size approaches carrying capacity. dN = r max N dt dt (K - N) K Fig

At what point is the “effective” r the highest? At what point are the most individuals added to the population? Are these the same?

Fits some populations well, but for many there is not stable carrying capacity and populations fluctuate around some long-tem average density. Logistic Model Fig

3. Life Histories How do we figure out r for different populations? What accounts for different patterns or rates of population growth among different species? –For example, different r max

a. Life History Tables : follow a cohort from birth until all are dead. life history table How do we figure out r?

Reproduction Tables : follow a cohort from birth until all are dead.

b. Life history strategies Life histories are determined by traits that determine when and how much an organism reproduces and how well it survives.

“big-bang” reproduction Vs. reproduction for consecutive years very high reproductive rates per event fewer young produced per event but often more parental care b. Life history strategies i. reproduction

Survivorship curves b. Life history strategies ii. mortality Fig. 52.3

There are often trade-offs between reproduction and survival. Fig European kestrel

Reproduction has a cost when energy is limiting. Fig – Red deer in Scotland

Near carrying capacity natural selection will favor traits that maximize reproductive success with few resources (high densities). Density-dependent selection. K-selection 3.b. Life history strategies iii. r- and K-selection Below carrying capacity natural selection will favor traits that maximize reproductive success in uncrowded environments (low densities). Density-independent selection. r-selection

Any characteristic that varies according to a change in population density. Density-dependent Any characteristic that does not vary as population density changes. Density-independent food availability, territories, water, nutrients, predators/parasites/disease, waste accumulation weather events, salinity, temperature

Space-limited Food-limited Density dependent: decreased fecundity Fig

Density dependent: decreased survivorship Fig

Density-dependent changes in birth and death rates slow population increase. They represent an example of negative feedback. They can stabilize a population near carrying capacity. Fig

Density dependent birth and death rates (as we just discussed). Many of these reflect –competition for resource (food/energy, nutrients, space/territories). –predation, parasites, disease –waste accumulation (e.g., ethanol) 4. Factors that limit population growth

Density independent survivorship or mortality –Extreme weather events –Fluctuations in wind and water currents 4. Factors that limit population growth

Interactions among population-limiting factors The dynamics of a population result from the interaction between biotic and abiotic factors, making natural populations unstable. Water temperature, Competition,Cannibalism. Fig

Population-Limiting Factors Some populations have regular boom-and-bust cycles. Predation Food shortage in winter Prey availability Fig

Population. Individuals same species occupying same general area. Have geographic boundaries and population size. Key characteristics Density. Individuals per unit of area or volume. Density. Individuals per unit of area or volume. Distribution: uniform, clumped, random. Distribution: uniform, clumped, random. Additions (+) : Births and Immigration. Subtractions (-) : Deaths and emigration. SUMMARY Demography. Studies changes in population size. Life histories. Affect reproductive output and survival rate and thus population growth. Life history strategies are trade-offs between survival and reproduction. Life history strategies are trade-offs between survival and reproduction.

Population Growth Exponential. J-shaped. Idealized, occurs in certain conditions. Exponential. J-shaped. Idealized, occurs in certain conditions. Logistic. S-shaped. A little more realistic. Carrying capacity. Logistic. S-shaped. A little more realistic. Carrying capacity. K-selection. Density-dependent selection. K-selection. Density-dependent selection. r-selection. Density independent selection. r-selection. Density independent selection. Population growth is slowed by changes in birth and death rates with density. Interaction of biotic and abiotic factors often results in unstable population sizes. In some populations they result in regular cycles.

6,417,531,489 people (as of 9:30, Feb. 8, 2005) 5. Human population growth

Questions 1.1. Human growth For example, -What factors are correlated with changes in human population growth rate? –How long has Earth’s population been similar to what it is now? –Over what time period has the human population shown the greatest change in numbers? 2. How do the patterns compare with what we have just studied about natural patterns of population growth? 3. What new questions does this raise for you?

Human Population= 6,339,110,260 (this morning) Exponential growth since Industrial Revolution: better nutrition, medical care and sanitation. Growth rates ( r ) Growth rates ( r ) 1963: 2.2%(0.022), 1990: 1.6%, 2003: 1.3% (200,234/day), 2015: 1% Growth will slow down either due to decreased births or increased deaths. Likely both as suggested by age- structure pyramids: relative number of individuals in each age-class. Fig

Age-structure pyramids Fig

BELLINGHAM CensusScope

When and how will human population growth stop? This question is likely to be answered one way or another in your lifetime. What is Earth’s carrying capacity for human’s? Have we already exceeded K? What are consequences of human population growth for other species on this planet?

Human impact Depends on –Total human population –Consumption by each individual –Ecological impact of each unit of consumption I = PAT (Ehrlich and Ehrlich) –P = population –A = affluence –T = technology

Unknown what the carrying capacity of Earth for humans is. A useful concept is the ecological footprint: land needed to produce resources and absorb wastes for a given country. World Wildlife Fund for Nature

Fig – Ecological footprints for various countries and the world

Human population has been growing exponentially for a long time. A reduction is expected either through lower birth rates or higher death rates. The age-structure suggest different scenarios for individual countries. Humans appear to be above Earth’s carrying capacity. SUMMARY