Ecology Lecture 8 Ralph Kirby

Life History Patterns GrowthDevelopmentReproduction Their interaction with other organisms gives rise to the organisms fitness One of the most important aspects of fitness revolves around the type of reproduction stragegy

Sexual or Asexual Reproduction Asexual reproduction –Rapid –If fitness is high, matches organism to environment –If fitness is low, possible extinction –Stress can result in use of sexual cycle to give new gene combinations Sexual Reproduction –Greater energy commitment Specific organelles Mating rituals Feeding offspring –Cost not equal between sexes –Can produce new gene combinations able to cope with a changing environment –Greater loss due to selection against divergent genotypes in a static environment

Types of sexual reproduction Dioecious –Most familiar Sexes are separate individuals –Greatest diversity of offspring Hermaphroditic –Perfect Male and females organs in same flower –Can result in significant inbreeding –Monoecious Separate male and female flowers –Reduces but does not eliminate inbreeding –Simultaneous hermaphroditic Both sets of organs at same time –Earthworms –Outbreeding, but maximizes offspring –Sequential hermaphroditic First one sex then the other sex –Mollusks, echinoderms and some plants. Sometimes animals –Allows all individual to participate in both sides of sexual cycle

Mating Strategies Different mating stategies have different advantages and disadvantages –Monogamy Seasonal or permanent –Allows sharing of cost of raising offspring –Increases survival chances of offspring –Many bird species and some mammalian species –Cheating does occur and has specific advantages to fitness –Polygamy More than one mate of one sex for a single individual of the other sex –Free individual to compete for resources and protect territory –Better food etc for mates –Some protection of offspring from competition –Promiscuity Greatest number of offspring Large amount of competition Female only responsible for offspring in terms of resources –Poorer survival change for offspring

Sexual Selection For Monogamy, Polygamy and Promiscuity –All involves the selection of a mate and therefore sexual based selection –Results in sexual dimorphism –Selection for secondary sexual characteristics Peacock versus Peahen –Large tail feathers, more mating –Smaller tail feathers, less mating Deer –Characters that aid competition such as horns Humans –Faster sports car such as a Ferrari

What is the mate really looking for in sexual selection Sports car –Is this just a display Big red car that makes a lot of noise –Or does it measure resources Ferraris are expensive In most cases the sexually selected characteristic is an indirect measure of resources or fitness –Bigger males have captured more resouces

Inbreeding If a population is small then inbreeding occurs –Self-fertilization Reassortment of genes but no new genes –A population in terms of genetics always has some degree of inbreeding Proportional to size of population Small population – Large inbreeding index Inbreeding depression –Rare recessive alleles become homozygous and are deleterious –Only when outbreeding between populations occurs is this avoided More new gene combinations Outbreeding depression –Maladaption to environment such as by colour

Reproductive Effort Reproductive females invest less energy in growth, etc Iteroparousity –Multiple cycles of reproduction means the organism must balance growth, maintenance, escaping predators, defending territory, etc against reproduction When – early or late How many offspring Semelarity –One reproductive effort with all resources, then death –No balance necessary –Environmental effect can be disastrous

Number of offspring Produce helpless offspring –Altricial –Mice Longer period suckling –Robin Other bird feeds Produce more mature offspring –Bees Colonial care –Foxes Mating pair care –Humans Family care Grandmothers, Grandfathers, Aunts, Uncles, Brothers and Sisters Large Number –Less resources per individual –More chances of success Extreme with released eggs and sperm in fish, etc Few Number –More resources per individual –More chance of accidental loss Extreme with single offspring over long period like humans and elephants

Ruderal Small and rapid lifecycle to invade new sites. Large dispersal area Competitive Stable environment, slower lifecycle With more resources to growth Stress-tolerant Limited resources. Ability to adapt

Food supply is important to reproductive success

Birds in temperate regions have a larger clutch size than tropical birds Animals in temperate regions have a larger litter size than those in tropics –Food supply with longer day length? –Adaption to large climate variation to allow rapid regrowth after a poor season –Greater mortality in winter results in more food next spring

Habitat Selection Filling the available niches and keeping out competitors Exception humans –All habitats –Left Africa and adapted the environment rather than adapted to the environment

Communities, Guilds and Competition Organisms in a given area make up a community –Spatial –May be subset of whole community with some linking characteristics Organisms competing for the same resource make up a guild In both cases, the effects can be positive, negative or neutral

Species numbers in a community can vary from very abundant and dominant to rare by essential to the community Species diversity –Species richness How many species –Species evenness How many individuals Dominants –Big trees in a forest –Removal changes the character of the system Keystone –Predators –Removal changes limits of the system

–Food Web How resources move about in terms of predation, competition, parasitism, mutualism, etc Really much more complex

Communities have a defined physical structure than is relatively stable

Vertical as well as hroizontal structure

One community can have more than one zone

Defining the edges of communities can be both complex and difficult Statistical Scale dependent Changes with time over the year Changes with time over longer periods –Primary New environment –Volcanic island –Secondary After disturbance –Human –None human

Year

Longer period

Succession works for the whole system

Over even longer periods with climate changes Ice Ages –Expansion and contraction of species in communities

How environment can affect communities Does clustering exist? –Sub-groupings AssociationsEcotones Or is there a continuum? –No sub-groupings Probably both