Examen parcial: Integrative Ecology of the Central Andes

1. What are the main climatic drivers in Peru?

1. Orographic barrier (Cordillera of the Andes)

2. Cool waters (Humboldt current) 

3. Meridionally shifting Intertropical Convergence Zone (ITCZ) and South Pacific High (Anticyclone)

4. Interannual ENSO (El Niño Southern Oscillation) events

What is unique about the biodiversity of the tropical Andes?

Biodiversity hotspot: high species diversity, high endemism

What is the convergence zone?

Oceanic Nazca plate descends under continental South American Plate (subduction) driven by sea floor spreading

What determines the presence or absence of volcanic zones in S. America?

The degree of subduction (Volcanic gap in the central andes due to shallow degree of subduction)

What is biodiversity? What are three different levels of diversity? 

• Variety of organisms present in an ecosystem (Complexity of living nature)

• genetic, species, and ecosystem diversity

What are two common measures of biodiversity?

1. Richness

2. Evenness

What is species richness?

the number of different species present

What is species evenness?

The distribution of abundance across the species in a community (if a habitat has a similar abundance for each species present → high evenness)

What are ecosystem services?

• The benefits people obtain from ecosystems

What are the 4 types of ecosystem services? Give two examples for each

• Regulatory: air quality, climate, water quality, erosion, diseases/pests, pollination, moderation of extreme events

• Provisioning: food, raw materials, medicinal resources, fresh water

• Supporting: nutrient cycling, photosynthesis, soil formation

• Cultural: mental/physical healthy, recreational/ecotourism, aesthetic values, spiritual/religious

What are 4 measures used to determine current trends in biodiversity? 

• Living Planet Index: measure of the state of the world’s biological diversity based on population trends of vertebrate species from terrestrial, freshwater, and marine habitats 

• Red List Index: extinction risk for groups of species 

• Biodiversity Intactness Index: how intact terrestrial biodiversity is compared to the year 1800

• The number of extinctions: cumulative number of species known to have gone extinct (longer-term trend from 1500)

What does the Living Planet Index indicate about current biodiversity trends?

Average size of vertebrate populations have declined 73% between 1970 and 2020

Why should we be concerned about species population sizes?

When species populations fall below a certain level it can cause ecosystems to weaken

Where have the worst losses in the Living Planet Index occurred?

Latin America (-95%)

How do current rates of extinction compare with the past? What is predicted for the future?

Current rates of loss exceed those of the historical past (fossil record) by several orders of magnitude. No indication of slowing (projected future extinction rate is >10x higher than the current rate)

What are 5 major contributors to the recent/current trends in biodiversity?

• changes in land/sea use (including habitat loss and degredation)

• species overexploitation

• climate change

• pollution

• invasive species

Why is biodiversity loss a concern? What are 3 negative consequences of biodiversity loss?

Biodiversity is essential for ecosystem services and therefore human well-being

• Worsening health: balanced diets, air pollution…

• Higher food insecurity

• Increasing vulnerability (natural disasters: hurricanes, flooding, wildfires…)

What is an ancient example of how biodiversity loss can threaten human populations?

Nazca people in Peru:

• civilization likely fell due to huge floods that wiped out settlements and irrigation systems

• people would have survived if they had not cleared native huarango trees for agriculture

• Huarango: large root systems absorb large amounts of moisture and stabilize soil, protection from winds

What is biogeography? 

Study of the distributions of organisms in space and time (can be studied with a focus on ecological factors that shape distributions or historical factors that have shaped current distributions)

What did Alexander Humboldt contribute to the study of biogeography?

• Delineation of “isothermal lines” (longitude/latitude?)

• Geography of plants: how distribution of organic life is affected by varying physical conditions

• Discovered decrease in intensity of earths magnetic field from the poles to the equator

• showed that distribution of volcanoes in America corresponded with vast subterranean fissures

• Described cold, low-salinity ocean current that flows north along the west coast of S. America which is one of the major upwelling systems of the world (Humboldt)

What are disjunct distributions of species?

Clearly related species (or even the same species) are found in two or more regions which are separated

What is paleobiogeography? What processes does it look at?

• Historical biogeography: studies the past distributions of species

• paleogeographic processes: especially plate tectonics

• looks at evolutionary history of species in order to determine why a certain species may have developed in a particular area

What is speciation? 

evolutionary process by which populations evolve to become distinct species 

What is allopatric speciation? What are the major steps leading to speciation?

when one population becomes geographically isolated from the rest of the species and different selective pressures result in speciation

1. Isolation (geographical)

2. Mutation

3. Natural selection

4. No interbreeding if barrier is removed

What is parapatric speciation? 

When a habitat gradient results in locally adapted individuals

• hybrid zone may form at the border (biological isolation)

What is natural selection?

When the presence of certain characteristics gives some individuals an advantage resulting in non-random survival and reproduction

What is the most important dispersal barrier (and route) in south america?

The Andes: may either serve as pathways for, or as barriers to, species migration

How did the geography of South America change over geologic time? What were the consequences for biodiversity?

1. Marine incursion: Western Andean Portal —> Isolation of Amazonian and North Andean Lineages (Late Eocene)

2. Gradual uplift of Andes creates a huge watershed (Pebas System) (Neogene)

3. Pebas System is drained and formation of the Amazon River initiated (Neogene)

What is the current understanding of what historical factors shaped current biodiversity in South America?

Origin of extant neotropical biodiversity is the result of complex ecological and evolutionary trends initiated by Neogene tectonic events and maintained by the action of Pleistocene climatic changes? 

What is the traditional hypothesis of how climate changes in the Quaternary led to current biodiversity?

Pleistocene climatic changes:

1. Glaciers link alpine zones into one continuous range

2. Glaciers recede: mountain pops become isolated → divergence/speciation

3. Glaciation: Alpine zones reconnected. Separately evolved species come back into contact

What is ecological biogeography? What are three major types of factors influencing it?

Looks at current factors responsible for distribution of plants/animals

1. Climatic factors

2. physiographic factors (altitude, steepness…)

3. biotic factors

What is ecology?

Study of the relationship between organisms and environment (biotic/abiotic)

What are three examples of abiotic/physical conditions that influence organisms?

• climate

• solar radiation

• water

• soil

• oxygen pressure

What are examples of biotic factors that influence organisms? 

• seeds

• diseases

• humans

• vegetation 

What is the biological definition of a species? What type of species does this definition not apply to?

A group of organisms with similar genetic information, structure, function, and behavior that are capable of interbreeding with one another and producing fertile offspring in nature (reproductive isolation)

• not relevant to organisms capable of asexual reproduction

What is the definition of a population? What are some of the ways populations are described?

A group of organisms of the same species occupying a particular space at a particular time

Populations can be described in terms of: size, density, dispersion, age structure…

What are three types of population dispersions? What might be the reasons behind these distributions in nature?

• Random: rare in nature 

• clumped 

  • social behavior, patchy dispersion of resources, asexual reproduction…

• Uniform

  • resource limitations, territoriality, competition…

What is a community? What are some of the ways that organisms interact with each other in a community? 

A group of interacting species that inhabit a particular location at a particular time 

• competition, predation, parasitism, mutualism, commensalism…

What is an ecosystem?

A community of living organisms in conjunction with the nonliving components of their environment, interacting as a system

What is a foundation species?

Species which have large effects on other species and play a major role in creating/maintaining a habitat that supports other species because of their considerable size or abundance (trees, corals..)

• usually primary producers that dominate an ecosystem in abundance and influence

How is a keystone species different from a foundation species? 

Keystone species have large effects not because of their abundance but because of the vital roles they play in their communities (disproportionate impact on the ecosystem when compared to abundance)

What is the competitive exclusion principle?

Only one species can occupy a whole niche in an ecosystem at a time. 2 species cannot have exactly the same niche: both compete in the niche for resources, nesting sites, or territory. One of the species will be superior to the other in utilizing the niche.

What is ecosystem resilience? 

Capacity of an ecosystem to respond and adapt o a perturbation or disturbance by recovering quickly

Resilience measures how quickly a system recovers from a disturbance and returns to a steady state 

What is ecosystem resistance?

Property of communities or populations to remain “essentially unchanged” when subject to disturbance (opposite is sensitivity)

Ability of an ecosystem to maintain characteristic processes despite various stressors or disturbances

What are some potential reasons for the high biodiversity in tropical areas (close to equator)?

• Less seasonality

• higher solar radiation → primary productivity

• higher temperatures

• higher humidity —> water availability

What pattern has been found about the relative abundance of species within ecological communities?

Most individuals belong to a few common species - similar pattern over wide range of ecological communities

What are the environmental characteristics of a desert ecosystem? 

• low rainfall (gain less precipitation than their potential evapotranspiration)

• Intense sunlight and heat 

• Wide temperature range (diurnal/seasonal) 

• Sparse vegetation

• Large surfaces of bare soil

What is unique about the Atacama-Sechura Desert (coastal desert)?

• Likely the oldest extant desert on Earth

• one of the driest environments

• Many endemic plant and animal species

Where can most of the plant life be found in the Atacama-Sechura Desert

Riparian zones (along rivers) and Lomas 

What contributes to the climate in the Atacama-Sechura desert?

• Humboldt current: cools down air on the coast preventing convection/precipitation

• Year round prevailing S. pacific Anticyclone and coastal inversion layer inhibit precipitation events

• Andes prevents humid air from Amazon from reaching the coast

What appears to be the limiting factor for vegetation growth in the Atacama-Sechura Desert? What evidence do we have for this?

• Water availability

• Desierto florido (flowering) after rainfall events indicates that nutrients are plentiful

What characterizes the Northern Coastal Desert? 

• Broad coastal plain: low topography provides a broad arid zone (without vegetation)

• Low shrubs dominate sparse vegetation below 100m, cacti increase in importance with higher elevation

• Active dunes 

• Seasonal temperature differences 

What are some adaptations seen in perennial desert plants?

• Green bark for photosynthesis

• Dropping leaves during dry season to prevent water loss

• Thorns: protection against herbivores

• No roots (i.e air plants which get moisture directly from the air)

• Very long roots to reach the water table

• Rosette growth form (collects water from atmospheric humidity)

• Foliar trichomes: nutrient and water uptake from atmospheric moisture

• Leaf waxes

• CAM plants: night time fixation of CO2 into malic acid (allowing stomata to open only at night)

• Succulence: accumulation of Na+ (salt) in the vacuoles, causing them to absorb/store water 

• Ability to reproduce both sexually and asexually (depending on the conditions) 

• white hairs on cactus reflect sunlight and reduce effects of high temp

What characterizes the central coastal desert north of Chimbote?

• Flat landscape with some isolated mountains (<600m)

• Desert areas nearly free of vegetation divided by irrigated river valleys

• some of the richest agricultural lands in Peru (nutrients/minerals from the Andes - carried by rivers)

What characterizes the central coast south of Chimbote? 

• Narrow coastal plain

• Lomas 

• Between Lima and Pisco, the coastal plain disappears and the landscape is dominated by the foothills of the western Andes 

• Many river valleys draining the mountains with extensive agricultural use

What characterizes the southern coastal desert?

• broad coastal plain (largely below 300m)

• sandy plains are free of vegetation

What are some of the ecosystem services provided by desert plants? 

Regulatory

• stabilizing dunes

• desalination/phytoremediation of soils (halophites: plants that grow on salty soil and accumulate salt and other heavy metals)

• Reduction of wind erosion 

• Reduction of water erosion

• Modifications of microclimate (soil/air temp and moisture)

Supporting 

• Increase soil nutrient content: legumes fix atmospheric N, tree litter fall, root turnover, increase microbial biomass

Provisional

• Food

• Forage 

• Fuel

• Shade/habitat

What are some adaptions of annual plants to desert climate?

• rapid growth when water is available

• seeds that can lie dormant for years

• subterranean bulbs, rhizones, and onions for nutrient storage

Where can Lomas be found? What characterizes them?

Between 5 and 30 degrees S along the hyper-arid coast-belt of western south america

• exclusively 100-800 masl

• depends on air-moisture during humid winter season

• high biodiversity

• high species endemism

Climate and geographic factors contribute to the formation of Lomas? 

• Humboldt cooling (especially in winter season) maintains near-permanent inversion layer at ~1000 masl

• Underneath moisture penetrates inlands driven by the S. Pacific High sea-winds and develops a near-permanent fog stratus layer

• Steep coastal slopes intercept clouds → fog-zone develops 

• relative humidity is >80%, drizzle events are frequent

What is a biogeochemical cycle? What are the main cycles? 

pathway by which a chemical substance moves through biotic and abiotic compartments of earth 

• carbon, oxygen, nitrogen, phosphorus, sulfur, and water

What characterizes tropical dry forests?

• closed canopy on fertile soils

• rainfall less than ~1800mm per year

• period of 3-6 months receive less than 100mm per month during which vegetation is mostly decidous

What are deciduous plants?

lose all of their leaves for part of the year

Why are dry coastal forests important in Peru?

• High level of species endemism

• Important role in controlling northward advance of the Sechura Desert

• Sequestration of carbon (large quantities)

What characterizes the climate of dry coastal forests? 

• warm and dry

• rainy season from January to March (100-500mm)

• well-defined dry season

• topography is generally flat with plains and low hills in coastal areas and small mountain chains toward the continent’s interior

• Water is most important limiting abiotic factor 

• large areas covered. by seasonal dry forests that grow green during rainy season

What some plant adaptations in coastal dry forests?

• Dropping leaves during the dry season → renewing canopies with the onset of rains (grow leaves at a heightened rate due to short length of rainy season)

• Green bark: trees can still photosynthesize even without leaves

• Storing water in cortical cells in trunks (can give these trees a swollen appearance)

• Capturing and fixing nitrogen in their roots → improving habitat conditions (i.e legumes)

• Tree growth concentrated in years with unusually high precipitation → tolerance to several years of suboptimal growth conditions

How do El Niño events effect coastal dry forests?

• Study: N. Peru ENSO fundamentally shapes these ecosystems

• During El Niño precipitation events: increased growth of all species

• Can even result in forest recolonization in arid areas of the Sechura desert (extreme events)

1. What type of population growth is typical of less-developed countries?

2. More-developed?

1. Increasing population

2. Decreasing population

What characterizes habitat degradation? What are the primary factors driving it?

Soil fertility decline and species loss

• Primarily: Anthropogenic activities: land use and land cover change (settlements, exploitation/harvesting of resources)

• climate change, natural disasters, geologic processes, chemical substance, invasive species introductions

What is Earth’s overshoot day?

Date when humanity has exhausted nature’s budget (biocapacity) for the year

What is sustainable development?

Development that meets the needs of the present without compromising the ability of future generations to meet their own needs

• meeting the essential needs of the human pop (particularly the poor)

• limitations imposed by the state of technology and social organization on the environment’s ability to meet present and future needs

What is sustainability? (three main components)

Equilibrium of environmental, social, cultural, and economic needs

What does research indicate about the speed of dispersal and the number of migrations that occurred during the first settlement of the Americas?

• Settlement of the americas happened very quickly (not slow/linear but highly dynamic)

• Multiple migrations: several waves and population branches which later mixed in different ways depending on the region

How did the Andean uplift influence S. American biogeography?  

• changed regional climate

• changed river drainage systems 

• produced huge amounts of sediments that filled up the amazon basin

What forces and processes explain the Andean uplift?

• Subduction in the Central Andes during the Paleogene

• Pacific Plate breakup and collision with S. American and Caribbean plates causes northern mountain building

How does geologic history explain some extant biodiversity in S. America?

• Andean uplift: nutrient-rich Andean-derived soils in the Amazon → high soil fertility → productivity and diversity

• nutrient poor Eastern Amazonian craton

What were the major findings of the study on greening/browning trends on the pacific slope?

• They found a greening strip on the Pacific side of the Peru and northern Chile

• Strongest greening occurs in higher areas going south

• CO2 distribution does not justify formation of such a localized green band

• Factors driving this greening not limited to a single climate type → complex regional factors

Which reforestation forest type (agroforestry, tree plantation, or secondary forest) seems to provide the greatest ecosystem services?

Secondary forests: high carbon sequestration potential, high biodiversity, improve water regulation, cost-effective

Agroforestry: stores important quantities of carbon (less than secondary), some biodiversity, mixed effects on water regulation, does not result in permanent forest cover

Tree plantations: often result in high carbon losses (particularly fast-growth/exotic species), negative effects on hydrological services, no durable/effective forest recovery

What is the demographic transition model (DTM)? What are the major stages?

A model that explains population changes by showing the relationship between birth and death rate as a population develops:

1. Preindustrial: population grows very slowly because of a high birth rate (to compensate for high infant mortality) and a high death rate

2. Transitional: population grows rapidly because birth rates are high and death rates drop because of improved food production and health

3. Industrial: population growth slows as both birth and death rates drop because of improved food production, health, and education

4. Postindustrial: population growth levels off and then declines as birth rates equal and then fall below death rates