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Evolution, Biodiversity, and Community Processes. Chapter 8. Biodiversity. How do we get Biodiversity?. Biodiversity. Biodiversity increases with speciation decreases with extinction Give-and-take between speciation and extinction changes in biodiversity
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Biodiversity • Biodiversity • increases with speciation • decreases with extinction • Give-and-take between speciation and extinction changes in biodiversity • Extinction creates evolutionary opportunities for adaptive radiation of surviving species
Interpretations of Speciation Two theories: 1. Gradualist Model (Neo-Darwinian): Slow changes in species overtime 2. Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change
Adaptive Radiation Emergence of numerous species from a common ancestor introduced to new and diverse environments Example: Hawaiian Honeycreepers
Convergent Evolution Species from different evolutionary branches may come to resemble one another if they live in very similar environments Example: 1. Ostrich (Africa) and Emu (Australia). 2. Sidewinder (Mojave Desert) and Horned Viper (Middle East Desert)
Coevolution • Evolutionary change • One species acts as a selective force on a second species • Inducing adaptations • that act as selective force on the first species Example: • Wolf and Moose • Acacia ants and Acacia trees • Yucca Plants and Yucca moths • Lichen
Extinction • Extinction of a species occurs when it ceases to exist; may follow environmental change - if the species does not evolve • Evolution and extinction are affected by: • large scale movements of continents • gradual climate changes due to continental drift or orbit changes • rapid climate changes due to catastrophic events
Extinction • Background extinction - species disappear at a low rate as local conditions change • Mass extinction - catastrophic, wide-spread events --> abrupt increase in extinction rate • Five mass extinctions in past 500 million years • Adaptive radiation - new species evolve during recovery period following mass extinction
http://www.geog.ouc.bc.ca/physgeog/contents/9h.html Mass Extinctions
Equilibrium Theory of Biodiversity • Diversity is a balance of factors that increase diversity and factors that decrease diversity • Production of new species (speciation), and influx can increase diversity • Competitive exclusion, efficient predators, catastrophic events (extinction) can decrease diversity • Physical conditions • variety of resources • Predators • environmental variability
Comparison of Two Communities • Richness (number of species) • Relative abundance • How do we describe these differences?
Biogeographical Changes • Richness declines from equator to pole • Due to: • Evolutionary history • Climate Fig 53.23 Bird species numbers
Geographic (Sample) Size • Species-area curve • The larger the geographic area, the greaterthe numberof species Fig. 23.25 North American Birds
Species Richness on Islands • Depends on: • Rate of immigration to island • Rate of extinction on island • These in turn depend on: • Island size • Distance from mainland
How do species move? • Humans (accidental and intended) • Animals (sticky seeds and scat) • Wind and ocean currents (+ or -) • Land bridges • Stepping stone islands • affected by climactic changes (glaciation) • ocean levels • short-term weather patterns
What allowed colonization? • Niche opening • No competition • Endemics not utilizing resources • Accessibility to colonists
Theory of Island Biogeography • Immigration rate decreases as island diversity increases • Extinction increases as island diversity increases • Species equilibrium on islands is a balance of immigration and local extinction
Theory of Island Biogeography • Smaller islands have lower total populations • Probability of extinction increases with lower population • Smaller islands have lower species diversity
Theory of Island Biogeography • Islands further from mainland have lower immigration rates • More distant islands have lower species diversity
Niche is the species’ occupation and its Habitat location of species (its address)
Niche A species’ functional role in its ecosystem; includes anything affecting species survival and reproduction • Range of tolerance for various physical and chemical conditions • Types of resources used • Interactions with living and nonliving components of ecosystems • Role played in flow of energy and matter cycling
Fundamental niche: set of conditions under which a species might exist in the absence of interactions with other species Realized niche: more restricted set of conditions under which the species actually exists due to interactions with other species Niche
Types of Species • Generalist • large niches • tolerate wide range of environmental variations • do better during changing environmental conditions • Specialist • narrow niches • more likely to become endangered • do better under consistent environmental conditions
r and k strategists • Depending upon the characteristics of the organism, organisms will follow a biotic potential or carrying capacity type reproductive strategy The r-strategists • High biotic potential – reproduce very fast • Are adapted to live in a variable climate • Produce many small, quickly maturing offspring = early reproductive maturity • “Opportunistic” organisms The K-strategists • Adaptations allow them to maintain population values around the carrying capacity • They live long lives • Reproduce late • Produce few, large, offspring
Types of Species • Native species normally live and thrive in a particular ecosystem • Nonnative species are introduced - can be called exotic or alien • Indicator species serve as early warnings of danger to ecosystem- birds & amphibians • Keystone species are considered of most importance in maintaining their ecosystem
Nonnative Species • Nonnative plant species are invading the nation's parks at an alarming rate, displacing native vegetation and threatening the wildlife that depend on them • At some, such as Sleeping Bear Dunes National Lakeshore in Michigan, as much as 23 percent of the ground is covered with alien species, and the rate of expansion is increasing dramatically.
Indicator Species • a species whose status provides information on the overall condition of the ecosystem and of other species in that ecosystem • reflect the quality and changes in environmental conditions as well as aspects of community composition
Keystone Species • A keystone is the stone at the top of an arch that supports the other stones and keeps the whole arch from falling • a species on which the persistence of a large number of other species in the ecosystem depends. • If a keystone species is removed from a system • the species it supported will also disappear • other dependent species will also disappear • Examples • top carnivores that keep prey in check • large herbivores that shape the habitat in which other species live • important plants that support particular insect species that are prey for birds • bats that disperse the seeds of plants
Competition Any interaction between two or more species for a resource that causes a decrease in the population growth or distribution of one of the species • Resource competition • Preemptive competition • Competition exploitation • Interference competition
Predator Adaptations • Prey detection and recognition • sensory adaptations • distinguish prey from non-prey • Prey capture • passive vs. active • individuals vs. cooperative • Eating prey • teeth, claws etc.
Prey Adaptations • Avoid detection • camouflage, mimics, • diurnal/nocturnal • Avoid capture • flee • resist • escape • Disrupt handling (prevent being eaten) • struggle? • protection, toxins
Herbivory Herbivore needs to find most nutritious • circumvent plant defenses Herbivory strong selective pressure on plants • structural adaptations for defense • chemical adaptations for defense
Symbiosis and symbiotic relationship are two commonly misused terms • Translation of symbiosis from the Greek literally means “living together” • Both positive and negative interactions
Mutualism DEFINITION: An interaction between two individuals of different species that benefits both partners in this interaction
