Lecture 5: Threats to Biodiversity (PDF)

Lecture 5 Threats to Biodiversity Continued!  Learning Objectives Same as those for Lecture 4 ! Explain what are the main threats to biodiversity in a concise and informative manner List the main causes of habitat loss and where it is more extensive Discuss the im...

Lecture 5 Threats to Biodiversity Continued!  Learning Objectives Same as those for Lecture 4 ! Explain what are the main threats to biodiversity in a concise and informative manner List the main causes of habitat loss and where it is more extensive Discuss the impact of habitat fragmentation on biodiversity Discuss the threats of exotic species on endemic biodiversity Explain the problem of overhunting and environmental degradation and what can humans do to minimize their effects Present an overview of how the effects of combined threats exaggerates the problems facing Nature and biodiversity Use the study case data and results effectively to build a case for an environmental problem facing the local community  Always go to the INTRODUCTION of any section and LISTEN TO THE eminent E.O. WILSON introducing the subject! Loading…  Habitat Fragmentation Look at the two figures in the introduction; very expressive! Effects of Habitat Fragmentation Involves the fracturing of a formerly continuous landscape into smaller and often isolated pieces Habitat fragmentation is usually accompanied with habitat loss No place for species or large populations to exist One inescapable result is the increased edge effect.…who can explain!? Look at figures Roads and power lines are detrimental! Another big problem is that caused by small populations that fragmentation creates Reduced genetic diversity DO NOT CLICK THAT LINK NOW!! We’ll come to it later!  Go to the link “more detail” Edge effect: read the definition Include invasion of exotic species Hotter, windier, and drier conditions Increased predation pressure, especially nest predators Proximity to humans can exaggerate the edge effects Increased hunting Increased environmental degradation: pollution Loading… Increased power lines and roads Road deaths are major cause of Florida Panther mortality Look at figures showing “pests” that thrive in edge habitats! Reduction and Isolation Fragmentation results in smaller areas Leads to smaller populations Less home range for larger species Less biodiversity; area can hold limited number of species  Reduction and Isolation, continued Isolated fragments will hold smaller populations inbreeding depression Many species can not cross edges between preferred habitat patches, while other species (airborne seeds, many birds) can Shredding What does that mean? Shredded habitats may experience higher edge effects but less isolation effects Again, look at figures!  Forest Fragments in Brazil Experiment designed to monitor the long-term effects of isolation on twenty five human-created rainforest fragments in the Brazilian Amazon. Long-term goal to determine how many species can be sustained in fragments of different sizes Only 11 plots remained after 20 years-the rest were abolished! Still the largest, most productive, and the main experimental study on the effects of habitat fragmentation One of the most important general conclusions of the project, however, is that there is no simple relationship between fragment size and species survival. Still, many maintain that given a choice between larger and smaller fragments, one should opt for larger areas Can support larger population, and would be subject to less edge effect  California Chaparral Fragmentation Highly diverse community-Mediterranean Classified as a hot spot (?) We will come to this in another lecture! Highly endemic (?)plant species prone to extinction 0.4% already extinct Chaparral is especially susceptible to problems of fragmentation, and the urbanization of southern California has accelerated this phenomenon. Endemic birds and rodents depend on chaparral community high extinction rates related to area and time since isolation of fragment High survival in larger and recently isolated fragments Could be exaggerated by mesopredator release process (?)  Highly endemic species in chaparral are found in small populations (this why there is high diversity: small populations and large richness); a whole habitat of many endemic populations may disappear with fragmentation Another problem is that chaparral endemic animals are unable to cross fragmented landscapes So, first, this will result in loss of species whose habitat has been fragmented Second, other populations of same species or another one will not colonize that empty habitat, since they will NOT cross boundaries between fragments Look at ALL figure!  Exotic Species Listen to the INTRODUCTION BY WILSON! Further thought question is another home work for you! Notice in all following examples that exotics are usually superiorly competitive to other native species! Examples … Fire Ant (Solenopsis invicta and Solenopsis richteri) Natives of S.A. and now spread into S.E. USA Look at ALL figures…IMPORTANT! Click on ANIMATION Exist in large numbers: 10’s of millions/ha (1000 m2 ) Drive big vertebrates away through their painful stings; See Fig on p. 2 Pests of invertebrates and many cereal plants and 139 native plant species, thus, keeping some pests populations down However, fire ants are displacing several native ant species READ the next two pages. What is interesting about the fire ants from a biological and human perspective? What is the biological agent used to control fire ants?  Examples…continued Purple Loosestrife Lythrum salicaria) A perennial plant native to Eurasia, now spread to most of USA See MAP figure Loosestrife degrades wetland ecosystems by forming large single-species stands that exclude natural vegetation and Loading… reduce habitat for wetland wildlife. Spreading rapidly via seed or vegetative reproduction, purple loosestrife flourishes in disturbed areas and has no natural enemies in N.A. Control measures such as herbicide application and mowing are generally not effective on established stands of loosestrife.  Affected states have recently begun biological control efforts, releasing two species of leaf-eating beetle and one weevil species (all from Europe, the origin of loosestrife!). Two important characteristics of loosestrife ensure strong competitive ability Vegetative reproduction Interbreeding of different strains through human activities Wetlands are severely affected by loosestrife It outcompetes native plants The problem is worse in wetlands already endangered Different practices to remove them are not successful on adult plants What are those methods? Biological control started 1996 using a type of beetle What is the beetle name and how specific they are?  Zebra Mussel Dreissena polymorpha) A mollusk, native to Eurasia, now spread to USA Individuals are 2 cm long and there can be 750,000/m3 ! Grow on any watery surface, including plants and inside pipes!! Exclude native mussel species; they grow on them densely! Look at figures…amazing power to spread on any surface! Click on animation Cause water shortage when block inside pipes and water systems Chlorination of water kills and removes mussels This harms all aquatic animals though, and not just zebra mussels Although some benefets there are more serious harmful effects READ that part…IMPORTANT!  Gypsy Moth Lymantria dispar) Gypsy moths are native to Europe and Asia; the European strain was introduced in Massachusetts in 1869 and has since become established in 16 states. The infestation area is now expanding at about 21 km per year. Look at figures; nice critter! During outbreaks, caterpillars cause defoliation of a variety of mostly broadleaf tree species, resulting in tree mortality and reduced fruit and leaf production. Eradication and control programs use biological and chemical insecticides, some of which have adverse effects on other species. The Asian strain, which may spread faster and target more tree species than the European strain, has recently been seen in several states. READ THE LEGEND OF the figure on p.2! Simple mistakes like these, and with other exotic species, resulted in environmental catastrophes!! Biological and chemical insecticides are being used to control this species During outbreaks, 15-35% of forest trees are damaged, leaving room for exotic plants to invade, and also reduces vertebrate species biomass  Mosquitofish Gambusia affinis and G. holbrooki) NA in origin; introduced into many parts of the world, especially those of highly endemic species (hot spots), to control for mosquitoes and the diseases they carry Mosquitofish are the most widely distributed fish in the world! They are 2-4 cm long; they eat many invertebrates, some fish, tadpoles, and larvivores Scientists did some work and showed they are NOT effective in mosquito hunting, the reason for which they were introduced to all over the world!!! In Australia, it was shown less effective in killing mosquitoes than native fish species! Drive some fish to extinction by either being superiorly competitive or by preying on their larvae and eggs! Called the “fish destroyer’! Mosquitofish can not tolerate cold, fast-running waters with high dissolved CO2; this makes native species avoid mosquitofish impact!  trophic cascade Did you remember to go to the links for each subject!?? Do this now! > - they