Habitat Fragmentation: Part II

1. Habitat Fragmentation: Part II

2. Biological Consequences of Fragmentation • Edge Effects • One of the best documented effects of fragmentation are ‘edge effects’ • Edge effects have mostly been examined in forests • Sunlight and wind alter the micro-climate at the forest edge, changing which plant species are favored

3. Biological Consequences of Fragmentation • In WI forests, edge zones of shade-intolerant plants may extend 10-15m into a forest (N,E,S) and 30m (W) • In Douglas Fir forests of Pacific NW, increased rates of blowdowns and other physical edge effects may extend over 200m into the forest • In Queensland, elevated rates of canopy and sub-canopy damage extend 500m in

4. Biological Consequences of Fragmentation • In some landscapes, especially in warmer climates, sealing of edges occurs through accelerated growth and increased regeneration of understory trees and shrubs • In some cases animals are then attracted to these edges, which may then function as an ‘ecological trap’ • In MI, songbirds nest at higher rates

5. Biological Consequences of Fragmentation • Consider the impact on birds • Roads and powerline corridors as narrow as 8m may produce edge effects • Cowbird parasitism may be significant for 100’s of m into a forest • Predation can also be significantly higher near the edges as densities and movements of raccoons, opossums, crows, foxes, jays, skunks, are all higher

6. Biological Consequences of Fragmentation • Artificial nest study of songbird nesting success

7. Biological Consequences of Fragmentation • Similar effects have been observed in a multitude of habitats and locations • Not all studies find ‘ecological traps’ in edge habitat, but most do find poor reproductive success • Highly fragmented systems, little edge effects are documented…why? • How do you think ‘edge effects’ in naturally heterogeneous landscapes compare? Why?

8. Biological Consequences of Fragmentation • Size and Shape • If edge effects are relatively pronounced or fragments are relatively small, the entire fragment may be edge • Consider a circular reserve of 100ha (250 acres) with a 600m edge

9. Biological Consequences of Fragmentation • 16 breeding sp of birds in WI • Similar total area, but different amount of ‘core’ areas with a 100m edge width • No ‘area sensitive’ birds nested in A, but 6 sp bred in B

10. Biological Consequences of Fragmentation • In tropical landscapes, human influences (i.e. hunting) generally extend several km into a forest, making smaller patches virtually void of game species

11. Biological Consequences of Fragmentation • Deleterious edge effects are quite the contrary to what many traditional views expressed in ‘wildlife management’ textbooks • It is true many of the traditional game species are edge species • However, in some areas species like deer are becoming a nuisance for people and plants

12. Biological Consequences of Fragmentation • Matrix Effects • The matrix surround habitat fragments in terrestrial landscapes distinguishes these patches from real islands • The amount of structural contrast between habitat fragments and the matrix in which they exist is one measure of fragmentation (severity of the filter)

13. Biological Consequences of Fragmentation • A structurally rich matrix may serve as a corridor for some and even suitable habitat for other species • For birds in ID, the landscape matrix determined sp richness within patches (relative to patch attributes themselvs) • When the matrix becomes more impermeable, the more isolated a patch becomes

14. Biological Consequences of Fragmentation • Undoubtedly on the main reasons results from fragmentation studies vary widely is the importance of the matrix itself • In general, the more different the matrix is from the fragments, the more intense the edge effects

15. Biological Consequences of Fragmentation • In MD, nest predation rates are higher in woodlot fragments surrounded by suburbs relative to agricultural fields • Similar results in Ontario • Why? • In CA, in patches that retained coyotes, songbirds had higher nesting success

16. Biological Consequences of Fragmentation • Roads • Habitat fragmentation is frequently accompanied by road building • It appears relative benign, but is NOT • Trombulak and Frissell (2000) • Mortality from construction, collision mortality, modification of behavior, alteration of physical environment, alteration of chemical environment, spread of invasives, & increased use by humans

17. Biological Consequences of Fragmentation • Most Amazonian understory birds respond negatively to roads and if wide enough (30-50m) will not cross • The endangered FL panther, auto collisions are the highest source of mortality • Small mammals in Ontario would not cross roads >20m wide • In the Mojave, of 387 rodents recaptured, only 1 was ever on other side • Turtles highly susceptible to roads (♀)

18. Biological Consequences of Fragmentation • Populations of the forest-dwelling carabid beetle were almost completely divided by a road and parking loops (unpaved)

19. Biological Consequences of Fragmentation • There can also be long-term effects at the genetic and community levels of organization • A German study from that separation of populations of common frogs reduced the average heterozygosity of both local populations; similar findings for a German study of bank voles

20. Biological Consequences of Fragmentation • However, while roads often serve as barriers to many native species, they frequently serve as a conduit for invasive species…why? • Plants are particularly well transported

21. Biological Consequences of Fragmentation • Species Invasions • The addition of undesirable species can have as large of an impact as habitat degradation or loss • In the US, this may be the 2nd leading cause of species endangerment behind direct habitat loss

22. Biological Consequences of Fragmentation • An additional problem with species invasion is the subsequent biotic homogenization, which can occur at several levels of biological organization (i.e. from genes to ecosystems) • One of the results of such a process is the loss of distinctiveness of communities (from genes to ecosystems)

23. Biological Consequences of Fragmentation • Effects on Ecological Processes • Ecological processes may change substantially as a result of edge effects • In addition to impacting avian population dynamics, fragmentation has also been shown to impact on area-sensitive species (particularly of top-predators), which can have cascading effects (Case Study 7.3)

24. Biological Consequences of Fragmentation • In forest fragments in OR, those surrounded by clearcuts have densities of deermice 3-4x higher, leading to increased predation on trillium seeds, which impacts recruitment and understory structure

25. Biological Consequences of Fragmentation • Invertebrates may be the strongest impacted due to their importance in nutrient cycling, decomposition, agents of disturbance • E.g. defoliation rates at edges > than core areas, densities of dung beetles being lower in smaller fragments, and lower abundances of soil invertebrates in smaller fragments

26. Biological Consequences of Fragmentation • There also appears to vulnerability of animal-plant mutualisms to habitat fragmentation (particularly plant-pollinator interactions) • As fragmented populations, many plant population become smaller where they may suffer from the Allee effect, where below some threshold size, pollinators no longer visit them

27. Biological Consequences of Fragmentation • Extinction rates of an annual plant related to pop(n) size

28. Biological Consequences of Fragmentation • One approach to mitigate the potential animal-plant is to establish corridors facilitating movements of seed dispersers and pollinators

29. Biological Consequences of Fragmentation • The landscape may also act to stop large-scale processes such as fire

30. Biological Consequences of Fragmentation • ‘Nested Species’ Patterns • The loss of species from fragmented landscapes may follow a predictable sequence • In studying habitat patches of various sizes, a pattern f nested subsets in the distribution of species is often observed

31. Biological Consequences of Fragmentation • A nested subset is a geographic pattern in which larger patches contain the same species found in smaller patches, along with additional species found only in larger patches

32. Biological Consequences of Fragmentation • For example, on mountain ranges in the Great Basin, which are natural habitat islands, boreal mammals and birds show a nested distribution pattern that may result from extinction of area-dependent species on smaller islands • Birds in woodlots show similar patterns • Birds in aspen stands (natural fragments)

33. Biological Consequences of Fragmentation • There can be other reasons for nested subsets besides a predictable sequence of extinction events (pattern vs. process) • Four processes which may generate nested patterns include: differential extinction, differential colonization, habitat nestedness, or simply an artifact of ‘habitat size’

34. Biological Consequences of Fragmentation • Species Vulnerable to Fragmentation • How can a sp survive in a fragmented landscape? • 1) a species might to well in the new matrix • 2) maintain viable pop(s) in single fragments • 3) be highly mobile and integrate multiple patches into a single ‘territory’ (corridors) • 4) none of the above…go extinct

35. Biological Consequences of Fragmentation • Populations in isolated woodlots in a fragmented landscape are higher in lots connected by fencerows than isolated lots

36. Biological Consequences of Fragmentation • Who is vulnerable to extinction? • Examine Box 7.2 • Wide-ranging species • Non-vagile organisms • Specialized requirements • Large-area or interior species • Low fecundity • Vulnerable to human exploitation

37. Biological Consequences of Fragmentation • Fragmentation vs. habitat loss • Sometimes it is extremely difficult to distinguish between fragmentation and habitat loss • We know the matrix is important • We know ‘regional’ composition is important

38. Biological Consequences of Fragmentation • Driving factors maybe different • Arden (1994) hypothesized that habitat loss would be the most important process explaining species declines in landscapes with a high proportion of suitable habitat whereas patch size and isolation would become more important in landscapes with a low proportion of suitable habitat

39. Biological Consequences of Fragmentation • In a computer simulation, Fahrig (1997) found that beyond 20% habitat cover, species persistence was virtually assured, regardless of habitat configuration • However, other studies have shown configuration can be very important, especially if considered over a relatively long time-scale

40. Biological Consequences of Fragmentation • Habitat fragmentation has not been nearly as well studied in the western US • Is there a need? Why? • Hansen and Rotella (2000) found only a single species that shared the LHC of eastern deciduous forests birds did that made them so vulnerable to fragmentation • They also found no edge effect in artificial nest predation studies in the Rockies

41. Biological Consequences of Fragmentation • Fragmentation in non-forest habitats • About 37% of grassland ecoregions in the western hemisphere are reduced to small and few fragments while another 15% are moderately fragmented • In the BBS, grassland birds have shown the greatest decline since 1966 (very high rates of predation and parasitism)

42. Biological Consequences of Fragmentation • Marine Fragmentation • Benthic habitats are subject to fragmentation • Mangroves, coastal wetlands, seagrass beds and reef systems are all highly fragmented • Estuaries and the fish residing within them are very susceptible to fragmentation

43. Biological Consequences of Fragmentation • Climate Change • Fragmentation is a threat in a stable world • If we add climate change, it may be ominous for many species • Species that are forced to move due to natural climate fluctuations have to deal with barriers (e.g. dams, pipelines) • New barriers may make movement tough

44. Biological Consequences of Fragmentation • For many species, it will be difficult to track shifting climatic conditions • High-elevation and high-latitude habitats may be lost entirely • Simulation models suggest wind dispersal is extremely poor in landscapes with <25% cover