Habitat Fragmentation - Lecture Slides | BIOS 406, Study Guides, Projects, Research of Conservation biology

Download Habitat Fragmentation - Lecture Slides | BIOS 406 and more Study Guides, Projects, Research Conservation biology in PDF only on Docsity! 1 Habitat Fragmentation • fundamentally different from habitat loss & degradation in that it involves changes in: • habitat area • habitat configuration Fragmentation illustrated by forest decline in much of US • changes in wooded area in Cadiz Township, WI show decreasing fragment size and increasing edge:interior (perimeter:area) ratio • Biological Dynamics of Forest Fragments Project (BDFFP) created series of 10-1, 10 & 100 ha (1 km2) fragments in 1980- 1984 near Manaus, Brazil • results were striking: primates, larger carnivores, army ants & termites (and ant- followers) quickly disappeared from all but largest fragments; but small mammals, frogs & butterflies increased; trees in smaller fragments had sign. edge effects 2 A process related to fragmentation is habitat shredding • occurs when linear habitat remnants are left after large scale clear-cutting • similar process in agricultural Midwest is termed “farmstead shelterbelts”; actually promoted for wildlife preservation • although such remnants may harbor significant diversity, they are a subset of the diversity of the intact rainforest In most communites, habitat mosaic is typically heterogeneous • Whittaker documented remarkable heterogeneity in Great Smokey Mts. National Park, TN • chestnut oak (O), chestnut (CH), pine (P), hemlock (H), beech (BG), fraser fir (F), etc. occurred in varying combinations on W- facing slopes Habitat heterogeneity also reflected by different quality patches • e.g., fire mortality of trees in Cook-Quentin area, Willamette National Forest, Oregon 5 Process of patch formation • typically, in forest comm., gaps created by disturbance are 1st step in fragmentation • gaps in rainforests create opportunities for gap specialists that may not persist in closed canopy • but increasing gap size may ultimately destabilize the community • in temperate rainforests of southern Chile and Argentina, gaps are quickly colonized by Chusquea quila, a fast-growing bamboo that eventually shades out all understory plants • the term “jungle” refers actually to disturbed tropical rainforest that has been clogged by undergrowth Far left: coastal rainforest w bamboo understory; Left & below: typical temperate rainforest in so. Chile Extreme fragmentation may result from replacement of native species by introduced ones • short-tussock grasslands in New Zealand have increased patchi- ness due to invasive grasses 6 Other effects of fragmentation include: 1. Initial exclusion --may be due to loss of rare endemics with small geographic ranges A stand of the ancient Wollemi pine, previously known only from impressions was discovered in a deep gorge in Australia in 1994 • Fossils date to the Jurassic, 200 mya; ~100 trees survive in Wollemi Nat.Park,120 mi W Sydney; grow to 40 m & live >1000 yr. • now threatened by a fungus-like disease, Phytophthora cinnamomi; detected in 2 trees in Nov. 2005 & almost certainly introduced by an unauthorized visitor • are being propagated in Australian botanic gardens Other effects of fragmentation include: 1. Initial exclusion 2. Crowding effects --appears due to lack of alternative habitat and concentration of remnant species into remnants (‘crowding of the ark’) 7 Other effects of fragmentation include: 1. Initial exclusion 2. Crowding effects 3. Insularization --Newmark’95 documented dramatic decreases in numbers of large mammals (especially carnivores) in most North American national parks --is probably due to fact that they have larger home ranges which are more likely to border edges --loss of species is apparently due to relaxation of species numbers • national parks & nature reserves probably act similar to land bridge islands over time; lose species by relaxation (a) • on other hand, oceanic islands accumulate species over time although they may never reach number of comparable mainland area (b) • many passerine birds fail to occupy smaller forest fragments; only occur in fragments many times the size of their territories 10 • edge habitats may present an “ecological trap” by attracting nesting birds & then increasing their exposure to brood parasites Brown-headed cowbird is most widespread brood parasite in U.S. --may cause up to 90% nesting failure in various songbirds --has over 200 potential hosts, & particularly severe effects on forest edges & urban areas --saturate even largest forest patches (~200 ha) and up to 800 m from periphery and predation • various conformations tested to determine extent of edge effects --Temple’86 found that 6/16 fragmentation- sensitive forest birds in south central WI bred in a fragment w 20 ha core area, but none in a long corridor area --39 ha corridor had no core area, whereas a 47 ha rectangular fragment had 20 ha core area (assuming 100-m edge width) Other effects of fragmentation include: 1. Initial exclusion 2. Crowding effects 3. Insularization 4. Isolation 5. Edge effects 6. Matrix effects --refers to propensity for species to recognize surrounding habitat as distinct from fragments which they originate --increasing 11 --until very recently, American crow populations have been increasing; recent decrease due to avian flu --unknown what their effects are on other birds --decreasing area & connectedness of forest patches has been a problem in many areas (here, Pacific Northwest) --if birds are strongly affected by incr. matrix of different habitats, then long- term strategies for their conservation must incorporate habitat management Other effects of fragmentation include: 1. Initial exclusion 2. Crowding effects 3. Insularization 4. Isolation 5. Edge effects 6. Matrix effects 7. Roads --even carabid beetles react negatively to roads avoiding movements across them --road barriers are particularly difficult for wildlife to negotiate --roads create a special problem for wildlife; not only isolate populations, but alter environment (light, runoff, salt, etc.) and can act as a killing field 12 --I-90 has numerous overpasses & underpasses in Snoqualmie Pass in the WA Cascades to reduce wildlife mortality Other effects of fragmentation include: 1. Initial exclusion 2. Crowding effects 3. Insularization 4. Isolation 5. Edge effects 6. Matrix effects 7. Roads 8. Species invasions --species invasions may be aided by fragmentation & roads because resident species populations are unable to resist them --IL was 38% forested in mid-1800’s; now only ~14% --many nonnative invasive plants have come to dominate IL flora; outnumber natives by 2X’s in cover --some may make up 90% or more of typical grassland & wetland plant species & cover 15 --Patterson & Atmar’86 develop. analysis tech. to determine degree of nestedness --perfect nestedness implies graded ability of species to disperse to various localities from source --e.g., fish in isolated Australian springs --nestedness doesn’t always have a clear explanation Fig. 14.7 Lomolino et al.’06 --Darlington’57 presented graphic representation of nestedness which he termed immigrant pattern; due to successively fewer sp. on more distant island; species-selective immigration occurs --“relict pattern” sugg. biota is result of random extinct. amg. sp. --relaxation model (Brown) sugg. that as A decr., biota converges on set sp. w resource needs --actual pattern prob. involves both I & Ex Fig. 14.6 Lomol. Species vulnerable to fragmentation typically have poor dispersal, specialized requirements and/or low in situ fecundity/recruitment Ontario white- footed mice show lower pop. growth rates in isolated woodlots than in connected ones… 16 Bay checkerspot butterflies (Euphydras) utilize highly patchy serpentine grasslands in California Central Valley --serpentine grasslands have highly specialized plant assemblage able to survive on high Mg, Cr, & Ni levels in soils --pops. w arrows are typically occupied; others are seldom so (unstable metapopulations); also suggests poor dispersal ability Olympic National Forest in Washington State has shown increasing fragmentation over time (re Lomolino & Perault Ecology 81:1517 [2000]) L & P compared small mammal assemblages in 3 forest types 17 Found that species richness declined from contiguous forest to clearcuts; also nonvolant forest specialists declined the most (dark bars) Ordination techniques (principal components analysis, PCA) showed that clearcuts were distinct in their small mammal faunas from fragments, corridors and continuous forest Example in Groom et al.’06 of islands in Lago Guri, Venezuela parallels results from islands in Lake Gatun, Panama --lake was created in 1986 by Raul Leoní/Guri dam on SA’s 2nd largest river, (Orinoco); lake is 2X’s size of Rhode Isld. Hydroelectric plant supplies of Venezuela’s electrical power