Introduced Species?

• Impact?– Growth pattern?– Causes?

Ecology

• What is Ecology?

• What Methods are used by Ecologists?

• What is a Population?

• What Factors Affect Population Size?

What can we learn about the moose population in Maine from these graphs?AET: Average evapotranspiration rates

Density and dispersion patterns are important population variables

• Clumped• Uniform• Random

Life Tables

• Survivorship Curves

Type I, II & III:

Q: Describe each in terms of…

Birth Rates?

Infant Mortality?

Post-natal Care

Survivorship curves are generated a by plotting the log of the fraction of organisms surviving vs. the age of the organism.

Characteristics of organisms which are extreme r or K strategists:

r: Unstable environment, density independent• small size of organism• energy used to make each individual is low• many offspring are produced• early maturity• short life expectancy • individuals can reproduce more than once in their lifetime • type III survivorship pattern in which most of the individuals die within a short

time but a few live much longer

K: Stable environment, density dependent interactions• large size of organism• energy used to make each individual is high• few offspring are produced• late maturity, often after a prolonged period of parental care• long life expectancy• each individual reproduces only once• type I or II survivorship pattern in which most individuals live to near the

maximum life span

Oyster, Hydra, Songbird…Man…..To compare different species, we normalize the age axis by stretching or shrinking the curve in

the horizontal direction so that all curves end at the same point, the maximum life span for individuals of that species. Notice that the vertical axis is on a log scale, dropping from 1.0 (100%) to 0.1 (10%) to 0.01 (1%) to 0.001 (0.1%) in equally spaced intervals.

 Survivorship data are important in studying the ecology of various organisms. Two components are involved in reproduction: 

1) How many females survive to each age and… 

2) ..the average number of female offspring produced by females at each age. By using these data, we can compute the intrinsic rate of reproduction, r, a key parameter in models of population growth.

Mathematical Models

– The equation G rN describes this J-shaped curve

• G the population growth rate

• r an organism’s inherent capacity to reproduce

• N the population size

Figure 36.4A

Time Number of Cells

0 minutes

20

40

60

80

100

120 (= 2 hours)

3 hours

4 hours

8 hours

12 hours

1

2

4

8

16

32

64

512

4,096

16,777,216

68,719,476,736

= 20

= 21

= 22

= 23

= 24

= 25

= 26

= 29

= 212

= 224

= 236

Num

ber

of b

acte

rial c

ells

(N

)

70

60

50

30

40

20

10

00 20 40 60 80 100 120 140

G = r N

Time (min)

Exponential Growth

Food Supply

Predation

Competition

Disease

4.0

3.6

3.8

3.4

3.2

3.0

2.8

0 10 20 30 40 50 60 70 80

Density of females

Clu

tch

size

Figure 36.5A

Factors Affecting Population Growth: Density Dependent Limiting Factors

– Abiotic factors

Density Independent Limiting Factors

Grey Seals @ Sable Island

• An interesting feature is that the continued increase in the number of grey seals has occurred in the face of considerable environmental change. Long-term environmental variability of the Scotian Shelf, the marine ecosystem primarily used by grey seals from Sable Island, is summarized in Zwanenburg et al. (2002). Interannual variability in water temperature and salinity in this area is among the highest observed in the North Atlantic. On the northeastern Scotian Shelf, the cold intermediate layer water oscillated near or above the long-term mean during the 1960s and 1970s, rose above normal in the early 1980s, fell sharply by the mid-1980s and remained below normal through the 1990s (Petrie and Drinkwater, 1993; Drinkwater et al., 1998). Continuous plankton recorder data of phytoplankton colour index, diatoms, and Calanus sp. show significant decadal scale changes between 1961 and 1998 (Sameoto, 2001). The influx of Arctic species is consistent with the colder waters during the 1990s. In addition, a major shift in the phytoplankton production cycle to the earlier months appears to have taken place, with corresponding changes in peak diatom abundance.

• Although changes at lower trophic levels are not expected to directly affect grey seal dynamics, bottom-up effects on prey might influence foraging success and hence reproduction and survival. Grey seals consume a variety of small pelagics, flatfishes, and gadoids (Bowen et al., 1993; Bowen and Harrison, 1994). Biomass of demersal fishes on the Scotian Shelf showed a stable to slightly increasing trend through the mid-1980s, but declined precipitously from the mid-1980s to the lowest value observed in the past 30 years. On the eastern shelf, biomass declined by 80% (Zwanenburg et al., 2002). Roughly coincident with marked declines in Atlantic cod (Gadus morhua) biomass and colder temperatures on the eastern shelf was a sharp increase in capelin (Mallotus villosus) and sandlance (Ammodytes dubius) abundance during the late 1980s and through the 1990s (Zwanenburg et al., 2002). Overall, the estimated total fish biomass increased through the 1990s and the average size of demersal fishes declined. Invertebrate abundance also changed with significant increases in snow crab (Chionocetes opilio) and shrimp (Pandalus borealis) over the same period (Zwanenburg et al., 2002).

•Limiting Factors and the Logistic Growth Model

– Limiting factors• Are environmental factors that restrict population

growth

Bre

edin

g m

ale

fur

seal

s(t

hous

ands

)

10

8

6

4

2

0

1915 1925 1935 1945

YearFigure 36.4B

– Logistic growth

• Is the model that represents the slowing of population growth as a result of limiting factors

• Levels off at the carrying capacity, which is the number of individuals the environment can support

Nu

mb

er

of

ind

ivid

ua

ls (N

)

K

0

Time

G = r N

G = r N

(K – N)

K

Figure 36.4C

Another Type of Population Growth Pattern….

The equation G rN(K – N)/K describes a logistic growth curve, where K carrying capacity and (K – N)/K accounts for the leveling off of the curve

Boom & Bust: Eastern Tent CaterpillarKingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Order: Lepidoptera

(unranked) Macrolepidoptera

Superfamily: Lasiocampoidea

Family: Lasiocampidae

Subfamily: Lasiocampinae

Genus: Malacosoma

Species: M. americanum

R-Selection Characteristics:

High reproduction early in life

Lots of offspring

High mortality

Type III Survivorship C

Exponential growth in favorable conditions

or then there is…K Selection

• K-selected species usually live near the carrying capacity of their environment.

• Population size is controlled by the availability of resources. In other words, they are a density dependent species.

• K-selected species have a long maturation time, breeding relatively late in life, a long lifespan, producing relatively few offspring, large newborn offspring, low mortality rates of young, and extensive post-natal. Examples of a K-selected species include elephants, bonobo apes and humans.

Intraspecific Competition!

P. caudatum

P. aurelia

AquacultureSustainable Resource Management

• Harvesting is done with the idea of sustaining maximum yield…why?

Human Population