Habitat Destruction and Fragmentation Flashcards
what are the 7 leading drivers of biodiversity loss (IUCN)
Overexploitation (e.g. logging, hunting, fishing): 6,241 species
➤ Maxwell et al. (2016) highlight that overexploitation alone threatens species like the Sumatran Rhino and Western Gorilla—75% of extinctions since 1500 were due to overexploitation and/or agriculture.
Agriculture (e.g. cropland, livestock): 5,407 species
➤ Agricultural intensification erodes biodiversity (Newbold et al., 2015).
Urban Development: 3,014 species
Invasive Species and Disease: 2,298 species
Pollution: 1,901 species
System Modifications (e.g. fire, dams): 1,865 species
Climate Change: 1,688 species
what is the trend of wilderness area change?
Human footprint index maps show minimal-impact zones are shrinking meaning less wilderness.
what has been the trend in land use and why?
Huge rise in land use since 1500—especially grazing (now ~5 billion ha).
Agricultural demands for protein are land-intensive: animal protein needs 10× more land than plant protein.
Even areas with historically low land conversion are now under threat due to global food system expansion (Newbold et al., 2015).
what is the current trend in human population and how does it affect land use?
Global population has doubled in just 40 years (1960–2000) and continues to rise.
Population growth + consumption in wealthy nations = massive pressure on biodiversity and land use.
what is the impact of agriculture on biodiversity? what did Newbold et al. show?
Agriculture causes both habitat conversion and intensification—leading to severe biodiversity erosion.
Newbold et al. show that local species richness is reduced by >32% in heavily cultivated areas like India, Europe, and South America.
what does fragmented habitats lead to?
fewer species than similar-sized contiguous habitats.
why does fragmentation reduce species richness? 3 reasons
Home ranges > fragment size (e.g. Grizzly bears need ~900 km²).
Isolated subpopulations can’t interact or migrate → higher extinction risk.
More edges = more exposure to external stressors (e.g., nest predation, light, wind).
what did Ewers & Didham (2008) find in beetle species for habitat fragmentation?
90% of 769 beetle species responded to edge effects.
Edge effects penetrated up to 1 km into forests.
Even large protected areas may not safeguard interior species due to large-scale edge effects.
what are matrix effects?
Species’ ability to traverse or use the surrounding matrix (non-habitat land) affects survival.
what did Campbell et al. (2011) find for matrix effects?
Pine plantations (low-contrast) = less damaging than pasture (high-contrast).
Edge biodiversity better preserved with compatible matrix types.
what are road effects on species
Roads fragment habitats, reduce movement, and increase mortality.
what did Shepard et al. (2008) find out about road effects
Turtles and snakes avoid crossing roads.
Leads to genetically isolated subpopulations over time.
Short-term stability can mask long-term genetic decline.
what is relaxation?
Fragmentation leads to delayed species loss over time. creates an extinction debt that may not reflect future stability.
what are the 5 characteristics making species vulnerable to fragmentation?
Naturally rare
Wide-ranging
Poor dispersers
Low reproduction
Short-lived
what did the long term case study by Laurance et al. (2008) find on fragmentation?
20-year study in Queensland shows:
Small fragments lost mammal species over time.
Specialists (e.g. Lemuroid ringtail possum) almost vanished.
Connectivity and fragment size were critical for survival.
Cyclones + matrix change affected recolonization.
