Lecture 8 Biodiversity: Habitat Fragmentation

The indigo bunting (Passerina cyanea) is a bird in the cardinal family that prefers to nest in edge habitat. If you were creating an indigo bunting preserve from intact forest, would you remove trees in 1 ha or 9 ha blocks? What range of forest removal would allow you to create the most indigo bunting habitat but still maintain significant intact forest for other organisms? Explain your answer.

To balance the edge-preference of this species and the interior-preference of other species, I would choose removal scenario of 1ha. This is because the 1 ha removal scenario is the only scenario that allows you to reach high levels (greater than 50%) of edge environment. This majority of edge environment would be crucial, as this reserve is specifically meant to be a sanctuary for the edge-preferring indigo bunting. Additionally, this removal scenario also allows for the maintenance of significant intact forest for other organisms at lower % forest loss. Specifically, if you stick with 10% loss for 1 ha removal scenario, you end up with about 40% interior and 50-60% edge.

How did differences in habitat loss scenarios (1 ha vs. 9 ha) affect the percent of edge habitat at different levels of remaining forest?

Up to % forest loss of about 50%, the amount of edge increases and it increases to a greater extent in the 1ha compared to the 9ha. After about 50% forest loss, this trend reverses; as you increase forest loss from this point, you start to see a reduction in edge habitat. It's a curved relationship because at first when you're decreasing the amount of forest (creating open patches in the forest), you're technically creating more edge. However, as those open patches start to predominate at higher % forest loss, you then begin to lose edge.

Threats from fragmentation

- limited dispersal and colonization (movement of offspring between patches) - reduced access to food and/or mates - limited habitat = smaller population sizes - edge effects

Which removal scenario (1 ha vs. 9 ha) results in more rapid loss of forest interior? Was the loss of forest interior a simple linear function?

As % forest lost increases, the 1ha removal scenario shows more rapid loss of forest interior than the 9ha removal scenario. In neither scenario was the loss of forest linear, but it was closer to linear (more constant rate of loss) for the 9ha removal scenario. A non linear function shows that forest interior is lost at a greater rate when low amounts of forest is removed, with that rate decreasing as you lose more of the forest.

Bigger or smaller fragment removal for interior-preferring species?

Bigger fragment removal (you lose less interior and create less edge)

Goal of fragmentation project in Brazil

Create artificial patches and measure lots of ecosystem variables before and after fragmentation

Difference between fragmented habitat and degraded habitat

Degraded habitat is uniformly crummy Fragmented habitat: Viable habitat but split up. Often has part of its habitat that's still high quality but other parts are bad

What is an edge effect?

Differences in the community near the edge of a fragment

How does microclimate change on the edge?

Differences in wind, rain, light. Canopy of trees provides cover from rain versus on the edge of canopy. Also wind and light differ Help contribute to differences in community composition

Differences in species richness are due to _______ after fragmentation

Extinction after fragmentation Smaller fragment size => causes more extinctions

Species richness trend for fragmented habitats

For the same plot size in hectares, fragmented habitats have fewer species than same area but not fragmented

What causes habitat fragmentation?

Humans - roads - logging - cultivation - cities

How does isolation (how close or how far apart these fragments are from each other) affect dispersal and colonization?

Increased isolation = decline in species abundance, decline in nutrient retention, decline in pollination, reduction in microclimate, reduction in species persistence, reduction in species richness

How do pioneer species, weeds, and invaders change at the edge?

Pioneer species: first species that arrive at a disturbed habitats Edges are disturbed habitats, and will be colonized by species that do well under disturbed conditions (pioneer species, weeds, invasive species)

How does fragment area influence species richness and extinction rates?

Reduced area = negative impact on species richness, community composition, nutrient retention (loss of nutrients occurs) Positive effect on microclimate => probably means increase in temperature Error bars are so large for abundance because the studies are across the world and there's lots of variation

The western white trillium (Trillium ovarum) grows in western North American forests. Although it is not at risk, it has a very low population growth rate and is sensitive to edge effects. Populations in intact forests have an annual growth rate of 2%, while populations that grow in edge habitat have a growth rate of -2%. Based on your data, is it better for trillium populations if logging removes trees in 1 ha or 9 ha increments? Explain your answer

Sensitive to edge effects. Want a scenario that leads to the slowest growth in edge effects. Because the 9ha removal scenario leads to a lower percent edge than then 1ha removal scenario, over nearly all of the % forest loss increments, you would want to choose the 9ha removal scenario for this species that is sensitive to edge effects.

How does fragment shape change the potential for edge effects

Shapes with more edge = more edge effects - ______

How does fragment size impact the effects of fragmentation

Smaller fragment = fewer species Similar relationship to species area curve

Bigger or small fragment removal for edge preferring species?

Smaller fragment removal (creates more edge)

How does community composition change on the edge?

Some organisms thrive in edge habitats, others cannot and some persist in spite of it Some specie shave a very narrow range of conditions that it can live in

Bigger fragment removed = higher or lower rate of gain of edge forest per increment of % forest loss?

The bigger the fragment (9ha versus 1 ha), the lower the rate of gain of edge.

Bigger fragments removed = higher or lower rate of loss of interior forest per increment of % forest loss?

The bigger the fragment (9ha versus 1 ha), the lower the rate of loss of interior forest.