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Behavioral ecology and evolution Lecture 4 9 August 2012 Sucking the planet dry Gleeson et al 2012 Nature… in YESTERDAY’S issue! Grey=magnification representing amount of water that people are currently pumping out of that aquifer, compared to the rate of natural replenishment. www.npr.org/blogs/thesalt/2012/08/08/158417396/heres‐where‐farms‐are‐sucking‐the‐ planet‐dry 2 http://www.nature.com/nature/journal/v488/n7410/full/nature11295.html#/access Sucking the planet dry • Water in most aquifers flows slowly underground feeding rivers and lakes 3 Outline: Behavioral ecology and evolution • Response to environmental variation • Theory of Evolution by Natural Selection – Variation within species – Balancing Selection – Behavioral changes via natural selection – Speciation – Patterns of Evolution • Adaptive behavior – All behaviors have costs and benefits – Territorial defense – Optimal foraging and diet width – Group living (costs, benefits, examples) 4 Response to Environmental Variation Each species has a range of environmental tolerances that determines its potential geographic distribution. • A fundamental principle in ecology and biogeography is that geographic ranges of species are related to constraints imposed by the environment. 5 Coping with the environment • Organisms have two options for coping with environmental variation: Tolerance and avoidance. • Spruce trees in the boreal forest cannot avoid temperature extremes so must be able to tolerate air temps that drop below –50°C in winter, and up to 30°C in summer. 6 Figure 4.1 A Frozen Frog An extreme example of tolerance 7 Figure 4.4 Climate and Aspen Distribution (Part 1) Climate envelope • A species’ climate envelope is the range of condition over which it occurs. • It is a useful tool for predicting a species’ response to climate change. 8 Response to Environmental Variation • Physiological processes have a set of optimal conditions for functioning. • Deviations from the optimum reduce the rate of the process. • Stress—environmental change results in decreased rates of important physiological processes, lowering the potential for survival, growth, or reproduction. • Stress can limit the range of species 9 Options vary over time • Many organisms can adjust to stress through behavior or physiology—called acclimatization. • Over time, natural selection can result in adaptation to environmental stress (next section) 10 Variation in Temperature • Ectotherms: Primarily regulate body temperature through energy exchange with the external environment. • Endotherms: Rely primarily on internal heat generation, mostly birds and mammals. 11 Figure 4.7 Temperature Ranges for Life on Earth 12 Outline: Behavioral ecology and evolution • Response to environmental variation • Theory of Evolution by Natural Selection – Variation within species – Balancing Selection – Behavioral changes via natural selection – Speciation – Patterns of Evolution • Adaptive behavior – All behaviors have costs and benefits – Territorial defense – Optimal foraging and diet width – Group living (costs, benefits, examples) 13 Hypotheses and Theories • Scientific Hypothesis: an explanation of events or observations • Scientific Theory: the highest level of scientific understanding, based on numerous hypotheses and years of study by many scientists. Evolution is a scientific theory 14 Theory of Evolution by Natural Selection • Natural selection is the mechanism that explains evolution • Natural Selection: scale = individual • Evolution: scale = many generations 15 Adaptation through natural selection “descent with modification” Evolution by natural selection: Over time, traits will be selected to match well with a particular species’ environment 1. Genetic variation (morphological, physiological, behavioral traits) • There is variation among individuals (we are each unique) • Some of this variation has a genetic basis and thus is inheritable (we can see which traits are truly genetic with common garden experiment) 2. Competition (“survival of the fittest”) • Organisms produce more young than can survive. 3. Differential reproduction (the “fittest” reproduce to pass genes on to the next generation) • Individuals with traits most suited to environment (i.e., with the greatest “fitness”) most likely to survive and reproduce. • Because they reproduce, these individuals have the greatest influence on the heritable characteristics of subsequent generations 16 Variation within species • Sexual dimorphism: secondary sex characteristic distinction • Sexual selection: selection towards secondary sex characteristics that leads to sexual dimorphism 17 Variation within the peppered moth (Biston betularia) • Industrial Melanism – dark color morphs dominate populations in industrial areas 18 http://porpax.bio.miami.edu/~cmallery/150/evol/melanism2.gif % Dark moths Variation Within Species 1811 dark moths were an uncommon morph 1848 1st dark moth found 1864 most common morph 1895 98% frequency! Smoke pollution control 19 Variation Within Species • Poecilia reticulata (a guppy) inhabits freshwater systems in northeastern South America • In Trinidad, downstream flow isolates populations in mountainous areas • In the absence of predation males are brightly decorated – AND, there is variation in the # and size of colored spots • Females prefer to mate with decorated males • Predators are absent in upper reaches 20 Variation Within Species Experiment 1. Three experimental populations, each with high natural variation in # spots/fish 2. Introduced different predatory pressures to different populations Weak Predators No Predators Dangerous Predators Endler 1980 • Balancing Selection – Two well‐adapted phenotypes, but in different environments 21 Balancing Selection • Heterozygote Advantage – When an individual who is heterozygous at a particular gene locus (e.g., they have both type A and B genes) has a fitness advantage over a homozygous individual – When heterozygotes are fitter than the homozygotes (AA or BB), natural selection will maintain a polymorphism hemoglobin gene HgbA HgbA HgbA HgbS HUMAN CASE STUDY: sickle cell anemia and malaria resistance HgbS HgbS 22 Genotype Life Expectancy Malaria Resistance Normal Hemoglobin Gene (HgbA) Normal No HgbA + HgbS Some Problems Yes Variant Hemoglobin Gene (HgbS) Short Yes 23 Malaria resistance Frequency of HgbS 24 Figure 4 Balancing Selection Source: Current Biology , Volume 21, Issue 18, Pages R718‐R725 (DOI:10.1016/j.cub.2011.08.022) Copyright © 2011 Elsevier Ltd Terms and Conditions 25 Outline: Behavioral ecology and evolution • Response to environmental variation • Theory of Evolution by Natural Selection – Variation within species – Balancing Selection – Behavioral changes via natural selection – Speciation – Patterns of Evolution • Adaptive behavior – All behaviors have costs and benefits – Territorial defense – Optimal foraging and diet width – Group living (costs, benefits, examples) 26 Behavioral changes via natural selection • Animal behavior=interactions with food, resources, mates, & other members of species group – Ex: Changes in feeding behavior lead to changes in bill shape and other specialized feeding traits 27 Darwin’s finches 28 Figure 6.11 Rapid Adaptive Evolution in Soapberry Bugs Speciation • So, that was variation within species. • We know that speciation also occurs. • When do we have speciation vs. just variation within species? 30 Speciation • What’s a species? – – • A group of living organisms capable of interbreeding to produce viable offspring Organisms belonging to two separate species cannot produce viable offspring. How do species form? – Usually (with many exceptions), populations of the same species 1. Becomes geographically isolated 2. Natural selection drives adaptation to the local environment 3. Reproductive isolation happens (e.g., Different courtship rituals) 4. If the two populations meet again: a) b) Cannot produce viable offspring: Speciation has happened! Can produce viable offspring, but their offspring are less fit then either of the “purebred” types, then natural selection will favor further reproductive isolation. Speciation has NOT occurred, but may happen in the future 31 Speciation • Darwin’s finches • Probably evolved from a single ancestor which was geographically separated from the mainland • At the Galapagos, ancestor evolved to exploit different resources on the islands: seeds, leaves, flowers, beetles, soft insects – Competition among the finches led to specialization, which led to speciation. • This richness of endemic species is typical for island chains. Because they are isolated 32 Mechanisms for isolating populations (leading to speciation): Allopatric and Sympatric • Allopatric speciation (a.k.a. geographic speciation) – Allopatry = Occurring in separate, nonoverlapping geographic areas. – Allopatric speciation can occur when biological populations of the same species become isolated – No secondary contact after initial isolation (at least for a long time) – Especially likely for island species 33 The grand canyon formed 5‐17 million years ago 34 South Rim: dry desert North Rim: ponderosa and pinyon pine forests Two squirrel populations diverged in characteristics over the last ~10,000 years 35 What would happen if we removed the Grand Canyon? (i.e., made the two populations sympatric?) 36 1. The squirrels breed with each other, and their gene pools mix freely. Still one species. 2. Speciation has occurred, making breeding impossible 3. The squirrels breed with each other, but gene flow only occurs in a small region where populations overlap (hybrid zone) 37 1. The squirrels breed with each other, and their gene pools mix freely. Still one species. 2. Speciation has occurred, making breeding impossible 3. The squirrels breed with each other, but gene flow only occurs in a small region where populations overlap (hybrid zone) In this case, are they two species or one?? ANSWER: One. But, speciation may occur in the future 38 Because two species are still able to breed with each other, should we consider them the same species? Or, since the gene pools don’t completely mix, should we consider them different species? 39 40 ALLOPATRIC SPECIATION In the process of allopatric speciation 41 Mechanisms for isolating populations (leading to speciation): Allopatric and Sympatric • Sympatric speciation – Sympatric = occurring in the same area – Sympatric speciation happens when genetic divergence occurs among groups of individuals living in the same place – Physical isolation is not necessary. Instead there is some form of ecological isolation between the groups. – Not many examples. Sympatric speciation is a debated subject. 42 Sympatric Speciation? • Apple maggot flies Rhagoletis lay eggs in: • (1) hawthorns (Crataegus) – Native to NE U.S. • (2) apples (Pyrus) – Apples introduced c. 300 ya • The flies belong to the same species; there is phenotypic plasticity in use of hosts. Individuals are simply responding differently to different environmental conditions • But, this specialization in host‐use may be the beginning steps towards sympatric speciation. 43 Speciation despite globally overlapping distributions in Penicillium spp: the population genetics of Alexander Fleming’s lucky fungus (various sps from a single ancestor) SYMPATRIC SPECIATION 44 Speciation despite globally overlapping distributions in Penicillium spp: the population genetics of Alexander Fleming’s lucky fungus (various sps from a single ancestor) “this apparently ubiquitous fungus is actually composed of at least two genetically distinct species” SYMPATRIC SPECIATION “little geographic population subdivision” “However, no hybridization was detected between the species” “competition [for resources] may facilitate species maintenance despite globally overlapping distributions” 45 Outline: Behavioral ecology and evolution • Response to environmental variation • Theory of Evolution by Natural Selection – Variation within species – Balancing Selection – Behavioral changes via natural selection – Speciation – Patterns of Evolution • Adaptive behavior – All behaviors have costs and benefits – Territorial defense – Optimal foraging and diet width – Group living (costs, benefits, examples) 46 Speciation may occur gradually, or in bursts (this continues to be debated) 47 Marine zooplankton Geological periods 48 Patterns of Evolution Divergent Convergent Parallel 49 Divergent evolution • Similar species become more and more distinct • Adaptation to different environmental conditions 50 Divergent evolution • Adaptive radiation is an example of divergent evolution – Ancestral species evolve into different species that occupy different niches (food habits) or habitats 51 Convergent Evolution • Acquisition of the same biological trait in unrelated lineages • Adaptation by different species to similar environmental conditions • Many examples – E.g., wings for flying in birds (Class Aves) and bats (Class Mammalia) 52 Parallel Evolution • Evolution of similar niches following isolation • Marsupials arrived on what would become Australia ~90 million years ago • The only other mammals present were monotremes (e.g., Echidna) • Adaptive radiation of Australian marsupials closely mimicked radiation of placental mammals on other continents 53 What leads to endemism? (species found nowhere else) • Small genetic input (the founder effect). Entire populations have the genetic make‐up of the founding couple. • Isolation ‐ no connection with mainland gene pool to dilute changes. • Unusual selection pressures. NOT no selection pressures, but very different to mainland life with diseases and predators. ‐ Given these conditions, evolution can act rapidly. ‐ Wallabies released on Hawaii in 1910 already have very different color, size and enzyme polymorphisms to Tasmanian populations. Possibly a new species (in only 100 years!). 54 Islands and Speciation • Isolation promotes endemism – Isolation can be due to geography and/or the dispersal ability of the organism – The evolution of endemic species on islands is strongly associated with species’ dispersal ability long‐horned beetles 55 Islands and Speciation • Endemism: A species found no where else – Common among island archipelagos, because they are isolated. • The island scrub jay, Aphelecoma insularis, found only on Santa Cruz Island, differs from the western scrub jay, Aphelecoma californica, by its larger size and stouter bill. – A result primarily of its diet incorporating the thick‐shelled acorns of island live oak, Quesrcus tomentella, another endemic species 56 Continental Drift and Evolution (isolation on a LARGE scale) • Patterns of speciation occurring on islands also occur on a much larger scale across continents – They all share a common ancestor (150 myr) 57 Evolutionary Perfection? • Evolutionary processes work with the genetic variation that is available – Survival of the fittest available, or fittest yet • Past events have profound repercussions on the present – Features acquired from ancestors influence fitness at present – Geography (continental drift, ice ages, etc.) • Environmental conditions can guide and limit evolution – Physical properties of air and water guide development of wings , flippers and fins – Gravity typically limits development of whale‐sized land animals 58 Fundamentals of Evolutionary Ecology • Individuals within a species are not identical • Some variation among individuals is heritable – Variation has a genetic basis • Most individuals die before reproduction – Among the reproducing minority, most reproduce at less than their maximal rate – i.e., not all young produced survive (to reproduce themselves) 59 Fundamentals of Evolutionary Ecology • Selective forces for and/or against particular traits • Selection affects survival and/or reproductive capacity of the individual • Selective forces: – Environmental: climate, physics – Ecological: species interaction (co‐evolution) – Both: Biophysical habitat conditions • Individuals with traits most suited to the environment are most likely to survive and reproduce – Because they reproduce, these individuals have the greatest influence on the heritable characteristics of subsequent generations 60 Adaptive Evolution • Rapid adaptive evolution can happen on a continental scale. • Clines are gradual changes in a characteristic over a geographic region. • Populations with adaptations to unique environments are called ecotypes. • Ecotypes can eventually become separate species as populations diverge and eventually become reproductively isolated. Littorina saxatilis, 6 ecotypes Littorina subrotundata, as found on barnacles Littorina subrotundata as found in marsh area Outline: Behavioral ecology and evolution • Response to environmental variation • Theory of Evolution by Natural Selection – Variation within species – Balancing Selection – Behavioral changes via natural selection – Speciation – Patterns of Evolution • Adaptive behavior – All behaviors have costs and benefits – Territorial defense – Optimal foraging and diet width – Group living (costs, benefits, examples) 62 Adaptive behavior • Trade‐offs= compromises between two activities – ex: foraging versus hiding from predators – ex: parental care versus reproduction and other activities 63 All behaviors have costs and benefits • Costs – energy consumed – probability of injury – risk to predation • Benefits – Survival rate – Reproductive success (# young / time) – Feeding efficiency (energy gained/ time) – Mating success (# matings/ time) 64 Territorial defense • Garibaldi adults defend a shelter hole, grazing area and sometimes nest site (red algae cultured by males) • Females allowed into site only to spawn, then males guard eggs until they hatch into plankton • intraspecific and interspecific defense (including humans!) • territorial defense may have evolved to increase reproductive success 65 Size of feeding territory and costs Optimal size is when benefits‐costs = greatest • Relationship varies across species, habitat, age, mating status, resource availability, etc • Optimal may not be actual due to additional factors absent from model 66 Consumer Behavior: Optimal Foraging a. Where is foraging concentrated? • Long‐term gain high but risk higher? • Intake lower but risk low? b. Does the location chosen just reflect the expected energy intake? • Or, balance with risk of predation? c. How long do consumers remain in one location before moving on? • Stay to avoid costly excursions? • Leave before local resource is depleted? d. What are the effects of competition? • Go where resource is abundant? • Go where competitors are few? e. Optimal diet width? • Specialist: Focus on one/few resources • Generalist: Expand diet to include many types of resources 67 Optimal Foraging Behavior • How have particular patterns of foraging behavior (e.g., specialist versus generalist) been favored? – Goal of any individual: Net intake of energy from a resource consumed > energy expended finding and handling (consuming) that resource • To obtain food, any predator must expend time and energy – Searching/finding the resource (s) – Handling the resource (h) • Pursuing • Subduing • Consuming 68 Optimal Foraging Behavior • While searching, a consumer will encounter numerous food items – Predator behavior characterizes it as a… Generalists OR Specialists – Consumes many types of resources Focuses on one/few resources 69 Optimal Diet Width Generalists Include low‐profitability items in their diet (because eats a variety of foods) Rate of energy intake is low, but steady (because access to many foods) Specialists Only include high‐profitability items (those most ‘worth’ the energy needed to get them) Rate of energy intake is mostly negative (because lots of time spent handing the food), but sometimes very positive (when resource is finally consumed!) How do consumers maximize the overall net rate of energy intake? 70 Optimal Diet Width • A predator’s perspective of a resource: – E = energy content of the resource – s = search time (time required to find the resource) – h = handling time (time required to capture, subdue and consume the resource) – E/(s+h) = net rate of intake = profitability of the resource to the predator • Assumption: Of all the resources in the predator’s diet, the predator will always choose to consume the most profitable one – If E/(s+h) is the highest possible for the predator, then definitely eats that resource • While searching for its most profitable resource, the predator encounters a resource of another type – s = 0, because already found the resource Enew Profitability of the new resource hnew Ebest sbest hbest 71 Optimal Diet Width “To eat it, or not to eat it?” That is the question E = energy content of resource s = search time h = handling time E/(s+h) = net rate of intake • When a consumer comes across a new resource it will: 1. Eat the new resource if: Enew Ebest hnew sbest hbest 2. Move on if: Enew Ebest hnew sbest hbest 72 Optimal Diet Width E = energy content of resource s = search time h = handling time E/(s+h) = net rate of intake • when the consumer comes across a THIRD new resource: 1. Eat the new resource if: Eaverage ( best 2 nd ) Ethird hthird saverage ( best 2 nd ) haverage ( best 2 nd ) 2. Move on (go look for the foods already in its diet) if: Eaverage ( best 2 nd ) Ethird hthird saverage ( best 2 nd ) haverage ( best 2 nd ) 73 Optimal Diet Width E = energy content of resource s = search time h = handling time E/(s+h) = net rate of intake • More generally: When a consumer comes across a new resource it can: 1. Eat the new resource if: Eaverage Enew hnew saverage haverage 1. Move on if: Eaverage Enew hnew saverage haverage Consumer will keep adding new resources to its diet if it can easily handle them compared with the time it takes to search for and handle existing resources in its diet 74 Optimal Diet Width: Some Insights • Specialists – Long handling times, relative to search times – Lions • Short search time, because live in sight of their prey • Long and energy-intensive handling time (includes stalking, chasing, consuming) • Thus, optimal strategy is to ‘handle’ only the most profitable prey: the old and weak Eaverage Enew hnew saverage haverage 75 Optimal Diet Width: Some Insights • Specialists – Long handling times, relative to search times – Owls: mainly nocturnal predators with exceptional hearing • Short search time, because can hear everything! • Long handling time, because takes energy to capture and digest prey • Thus, optimal strategy is to ‘handle’ only the most profitable prey – Small rodents Eaverage Enew hnew saverage haverage 76 Optimal Diet Width: Some Insights • Generalists – Short handling times, relative to search times – Insectivorous birds • Searching for insects takes time (not tons, but some) • Handling (consuming) an insect takes very little time • Thus, optimal strategy is to consume nearly every insect they encounter Eaverage Enew hnew saverage haverage 77 Optimal Diet Width: Some Insights • Generalists – Short handling times, relative to search times – Raccoons: will eat almost anything (including your trash) • Searching for food takes time (not tons, but some) • Handling (consuming) food takes very little time – Well adapted paws for capturing a variety of prey – Have strong gut for digesting lots of food types • Thus, optimal strategy is to consume nearly everything they encounter – berries, insects, eggs and small animals. Eaverage Enew hnew saverage haverage 78 Specialists and Generalist Predators Advantages to being a specialist 1. Avoid interspecific competition 2. Allows evolution to overcome chemical defense 3. Allows evolution of cryptic coloration that matches prey - mostly for insects on plants 4. Increases chance of mate encounter Advantages of being a generalist 1. Flexibility in face of environmental uncertainty 2. Broad diet needed to get all necessary nutrients and vitamins 3. Avoid overdosing on any one toxin - mostly for animals grazing on chemically defended plants 79 Outline: Behavioral ecology and evolution • Response to environmental variation • Theory of Evolution by Natural Selection – Variation within species – Balancing Selection – Behavioral changes via natural selection – Speciation – Patterns of Evolution • Adaptive behavior – All behaviors have costs and benefits – Territorial defense – Optimal foraging and diet width – Group living (costs, benefits, examples) 80 Group living Potential Benefits Potential Costs Increased foraging efficiency Intraspecific competition for food Reduced predation Increased risk of disease, parasites, and attraction of predators Increased access to mates Loss of paternity, brood parasitism Help from kin, indirect evolutionary success Loss of individual reproduction Evolution of traits that increase survival and reproductive success of kin=kin selection (Krebs Table 4.1) 81 Group living • Herbivorous herds (e.g.,caribou), schooling fish, carnivores, birds (e.g. starlings), 82 Group living in ospreys do not school school 83 (Krebs Figure 4.9) Group behavior in western gray kangaroos 85 (Krebs Figure 4.11) Group behavior: Starlings • Near Oxford ‐ England. This was filmed at an Royal Society for the Protection of Birds (RSPB) reserve called Otmoor. • http://www.youtube.com/watch?v =XH‐groCeKbE 84