Week 3 Lecture Notes - 13 Sept. 2012

We reviewed the AUC academic policy and the grading policy for this class.

Review –        

• Earth’s biomes           
• Latitude defines the location of the tropics – closer to the equator higher precipitation and temperature.
• Remember – There are many tropical ecosystems.  The tropical forest ecosystem (or biome) occupies 7% of earth’s surface, but includes 50% of the world’s biodiversity!

(see Neotropical Companion Chapter 4 pg 86; Tropical Ecology Ch 4 pg 120)

Latitudinal diversity gradient – the reduction in diversity with increasing latitude.

Breeding birds

Greenland 56 species

New York 195 species

Guatemala 469 species

Panama 1,100 species

Columbia 1,395 species

How many breeding bird species are on Hispaniola?  You would have to go through the Birds of the DR and Haiti book of 309 species and count which ones breed here (good paper subject!).

WHY is there a latitudinal diversity gradient? 

Environmental stress and Complex Physiognomy

1. Environmental stress

Lower in the tropics, higher in temperate and higher latitudes.

Polar and temperate climates impose physical stresses.

Remember the temperature ranges of each biome:

• Tundra temperature = -25C to 5C    (-13F to 41F)
• Temperate forest = Wide flux in temperature winter to summer  -5C to 30C (23F to 86F)
• Grasslands have even higher temps in summer
• THUS animals and species need to survive very cold winters and very hot summers

And less precipitation 

• Tundra 23 cm precipitation
• Temperate forest 81 cm
• Grassland 31 cm

Tropics – consistent rain and temperature!  Less environmental stress.

Mammals – 950 species of bats in world.

• 39% of all neotropical mammal species are BATS!  (they are in 75 genera)
• In higher latitudes (temperate regions), bats represent a lower percentage of mammals

• US has 423 mammal species, of which 40 species are bats, 9% are bats (with 2 feeding habits – insects and fruit)
• Belize has 84 species of bats
• Costa Rica has 103 species of bats
• Bats in neotropics have 7 different feeding habits – insects, fruit, nectar, carnivores, fish, blood, generalists

Majority of native mammals in Haiti are bats - 16 species

We watched videos about - reefs, bats, and hummingbirds.

2. Complex Physiognomy – Physical structure of an ecosystem.    

Plate 3-29 The complex physiognamy of a tropical forest (Tropical Ecology, Kricher)

Tropical forests have elaborate structure - trees, palms, ferns, vines, epiphytes, etc.  (see Plate 3.29 Tropical Eco.)

Thus more niches with less competition for any one niche, thus can support more species.

Ecological niche = place that an organism occupies in an ecosystem; both the ecological role and physical habitat that an organism occupies.

But how do we measure diversity?

Biodiversity = we had defined it as the number of species in an area, but it actually can be described by 2 concepts.

1. Species richness = Number of species within a given area.  Macaya report found 37 species of birds = species richness of 37.

But are there the same number of individuals of each species?  No, they found from 1 to 55 individuals of each species.

2. Evenness = how richness is distributed relative to population size. 

• Rated on a scale of 0 to 1.
• If there are the same number of individuals per species, evenness = 1.  This is high evenness, typical of tropics.
• If there are highly different numbers per species, evenness = 0.  This is low evenness, typical of temperate regions.
• Evenness is expressed as decimal number is in between.  0.15 is a lower evenness than 0.85.

Example: 100 doves, 1 parrot, 1 woodpecker.

Species richness = 3.  But is this really diverse?  Not very diverse since most of the animals are doves.

To evaluate diversity, we need to also consider 2 things: area sampled, and sampling effort.

Area

100 species are found in 10-square mile Park A, and 10 species are found in a 1-square mile Park B.  Can we say that Park A has a higher species richness?  No, we need to look at richness per unit area.  So:

• Park A  100 sp / 10 mi2 = 10 species per mi2.
• Park B  10 sp / 1 mi2 = 10 species per mi2.

Conclusion, they have the same species richness per unit area.

Sampling effort – Amount of time spent surveying (searching, sampling, etc.).

The more time you spend searching, the more species you will find (up to a certain point).

Spend 2 days searching in Macaya, but 4 days searching in Foret de Pines, you will probably find more birds in Foret.  But that doesn’t mean there are more birds.  Just that you spent more time looking.

So for research, you need to spend the same amount of time in both places so you know you are comparing them the same way.  That is why the Macaya paper went into so much detail about how long they spent searching in both sites.  To prove they spent the same sampling effort at both sites, thus could compare data and with confidence say that one site did have more birds than the other.

• 1 day surveying birds at AUC yields 10 species.
• 10 days surveying birds at the Botanical Garden yields 100 species.
• Which place had higher species richness?

You first need to put these into the same units of sampling effort:

• AUC  10 sp / 1 day = richness of 10 per day
• Garden 100 species / 10 days = richness of 10 per day

They are the same!

 

You will reach a point where you don’t find any more new species.  You see this on the graph where it levels out (the asymptote).

Figure 4-1 Tropical Ecology (Kricher)