Ecology -Communities-

Communities & Populations Ways to characterize communities Diversity Keystone species Disturbance and Succession • Processes at work in communities Competition Predation Commensalism/mutualism

Community - an assemblage of populations of various species living close enough to potentially interact.

Communities - Diversity Measuring Diversity -diversity is a measure that evaluates the number of species and the number of organisms in each species in an area

Communities - Diversity Shannon Diversity index natural logarithm H’ = -Σ pi ln pi Shannon diversity index proportion of ith species Sum of

Communities - Diversity Examples - intertidal zone in New Brunswick Sample and count the number of each species

Communities - Diversity Examples - intertidal zone in New Brunswick SPECIES Species 1 Species 2 Species 3 Species 4 Species 5 Species 6 Species 7 Species 8 Species 9 Species 10

Communities - Diversity Examples - intertidal zone in New Brunswick SPECIES NUMBER Species 1 71 Species 2 18 Species 3 1 Species 4 59 Species 5 5 Species 6 11 Species 7 15 Species 8 Species 9 Species 10 4 Total = 200

Communities - Diversity Examples - intertidal zone in New Brunswick SPECIES NUMBER pi Species 1 71 71/200 = 0.355 Species 2 18 18/200 = 0.09 Species 3 1 0.005 Species 4 59 .295 Species 5 5 0.025 Species 6 11 0.055 Species 7 15 0.075 Species 8 Species 9 Species 10 4 0.02 Total = 200

Communities - Diversity Examples - intertidal zone in New Brunswick SPECIES NUMBER pi lnpi Species 1 71 71/200 = 0.355 .126 Species 2 18 18/200 = 0.09 .008 Species 3 1 0.005 .000025 Species 4 59 .295 .087 Species 5 5 0.025 .0006 Species 6 11 0.055 .003 Species 7 15 0.075 .00562 Species 8 Species 9 Species 10 4 0.02 .0004 Total = 200

Communities - Diversity Examples - intertidal zone in New Brunswick SPECIES NUMBER pi lnpi pilnpi Species 1 71 71/200 = 0.355 -1.036 -0.368 Species 2 18 18/200 = 0.09 -2.408 -0.217 Species 3 1 0.005 -5.298 -0.026 Species 4 59 .295 -1.221 -0.36 Species 5 5 0.025 -3.689 -0.092 Species 6 11 0.055 -2.9 -0.16 Species 7 15 0.075 -2.59 -0.194 Species 8 Species 9 Species 10 4 0.02 -3.912 -0.078 Total = 200 H’ = 1.716 H’ = -Σ pi ln pi

H’ = 1.774 If we remove the two most common species, (was 1.716) NUMBER Species 1 71 Species 2 18 Species 3 1 Species 4 59 Species 5 5 Species 6 11 Species 7 15 Species 8 Species 9 Species 10 4 Total = 200 (was 1.716)

Imagine a community that has (potentially) 5 species of tree Look at 3 different forests

Forest 1 Forest 2 Forest 3

Forest 1 Forest 2 Forest 3 1 2 3 10 36 4 48 Total 50 H E

1 pi lnpi pilnpi 10 0.2 -1.61 -0.322 Total 50 1.61 H’ E

1 pi lnpi pilnpi 2 10 0.2 -1.61 -0.322 36 0.72 -0.329 -0.237 4 0.08 -2.53 -0.202 3 0.06 -2.81 -0.169 0.04 -3.22 -0.129 Total 50 1.61 0.938 H’ E

H’ E 1 pi lnpi pilnpi 2 3 10 0.2 -1.61 -0.322 36 0.72 -0.329 -0.237 - - 4 0.08 -2.53 -0.202 48 0.96 -0.04 0.06 -2.81 -0.169 0.04 -3.22 -0.129 Total 50 1.61 0.938 0.297 H’ 0.362 E

Shannon Evenness Index Shannon diversity index natural logarithm Total number of species

H’ E lnS = ln(5) = 1.61 lnS = ln(5) = 1.61 lnS = ln(3) = 1.098 1 pi pilnpi 2 3 10 0.2 -1.61 -0.322 36 0.72 -0.329 -0.237 0.04 4 0.08 -2.53 -0.202 48 0.96 -0.04 - 0.06 -2.81 -0.169 -3.22 -0.129 Total 50 1.61 0.938 0.297 H’ 0.362 E 1.0 0.583 0. 329 lnS = ln(5) = 1.61 lnS = ln(5) = 1.61 lnS = ln(3) = 1.098

Other measures of diversity Simpson’s Diversity Index (D) = 1/ ∑pi2 ∑pi2 means the sum of the chances of finding each species in the community

Communities - Diversity Often a single species can influence the structure of an entire community Keystone Species

Communities - Diversity Since 1700’s

Communities - Diversity - before hunting of sea otters - after hunting of sea otters

Communities - Diversity Keystone species

A second example – keystone species California Mussel - Mytilus Predatory seastar - Pisaster

A second example – keystone species California Mussel - Mytilus Predatory seastar - Pisaster

A second example – keystone species 1.5 Limit of mussel distribution above minimum tide 1.0 0.5 0 2 4 6 8 10 Time (Years) Pisaster removal begins Pisaster removal ends

Communities - Succession and Disturbance What is “disturbance”? Any event that changes a community, removes species from it or alters resource availability

Communities - Succession and Disturbance Kinds of disturbance Floods Glaciers Fire Invasive species Hurricane

Communities - Succession and Disturbance Is disturbance always bad?? - Intermediate Disturbance Hypothesis Competition reduces community diversity Frequent disturbance wipes out community Diversity Disturbance (frequency or intensity)

Communities - Succession and Disturbance Replacement of species in a habitat through a regular progression Usually after some disturbance

Communities - Succession and Disturbance Primary Succession - community is wiped out to mineral rock Secondary Succession - some soil or organic base left in community

Communities - Succession and Disturbance Succession - Krakatoa - eruption in August, 1883 most of island was destroyed sound heard 4500 km away 40m tsunami

Communities - Succession and Disturbance Succession - Krakatoa 1886 - 6 species of cyanobacteria 1890 - 11 species of ferns 1897 - Tall grass prairie 1919 - Scattered trees 1931 - Fig tree woodland 1980 - Rainforest Primary succession Secondary succession 1883

Communities - Succession and Disturbance Succession - Krakatoa Sea dispersed Wind dispersed Animal dispersed Number of species 1860 1900 1940 1980 2000 How did colonizers get there?

Communities - Processes between Populations + = beneficial to a species = detrimental to a species 0 = species is unaffected Kinds of Interactions Interaction Species 1 Species 2 Competition - Predation + Herbivory Parasitism Disease Mutualism Commensalism Same kind of interaction (+/-)

Communities - Processes between Populations + = beneficial to a species = detrimental to a species 0 = species is unaffected Kinds of Interactions Interaction Species 1 Species 2 Competition - Predation + Herbivory Parasitism Disease Mutualism Commensalism