Year 12 Investigate a pattern in an ecological community, with supervision

ECOLOGY

Biology 2.1 Carry out a practical investigation in a biology context, with supervision (AS 91153)

The assessment for this Achievement Standard will involve you carrying out a practical investigation to collect and interpret data to discuss the presence of observable community patterns. The community patterns will be selected from succession, stratification and/or zonation.

You will:

·      Develop a statement of the purpose of your investigation written as a hypothesis linked to a scientific concept or idea

·      Using a method that describes how the data that will be collected, range of data/samples, and consideration of some other key factors

·      Collect, record and process data relevant to the purpose of the investigation

·      Interpret and reporting on the findings

·       Reach a conclusion based on your processed data which is relevant to the purpose of the investigation

·       Identify and include relevant findings from another source.

The field trip to collect your data is scheduled for Thursday February 25. It is important that by this date you are able to:

1) identify the following New Zealand native plants:

2) Use a transect line to sample data from a forest community

3) Process data to produce a lolipop diagram

4) Discuss abiotic and biotic factors affecting plant growth specific to species in the Waitakere Ranges.


SUCCESSION

STRATIFICATION

Stratification is the pattern observed when vertical layering of different species is present. The picture below depicts a mature stratified forest community and some of the NZ native species that can be found within each layer (stratum). 

Healthy bush is characterised by a deep covering of leaves on the ground (leaf litter) which, together with rotting logs and branches, provide ideal growing conditions for a ferns, mosses, lichens and germinating seeds and seedlings.

Above the forest floor there should be an understory or shrub layer, and sub-canopy layer, making it difficult to see far into the bush before there is a ‘wall’ of vegetation. Shrubs such as coprosmas, kawakawa, pitosporum, mingimingi and tree ferns occupy the layer from a height of approximately 20 cm to 2.5 m. 

Above this, are the taller sub-canopy trees of the Waitakeres: manuka, kanuka, nikau, lancewood, cabbage trees, rangiora (mahoe, pate, putaputaweta and pigeonwood in other areas) which form a layer between the understory/shrub layer and the canopy.

Below the canopy you will also find saplings of various ages waiting to change from juvenile ("Christmas tree shaped" to adult "broccoli" forms once gaps left by older trees as they fall/die are left.

A healthy canopy will be almost continuous (except for tree-fall gaps) and will usually comprise a variety of species, with different trees dominating over time as they compete for space in the canopy. Common canopy trees in the Waitakere ranges are kauri, rimu and kahikatea (tawa, titoki in other areas). When looking up into the canopy you should see climbing vines (such as rata and supplejack) and different species of epiphyte e.g. Astelia (kowharawhara or perching lily)

      The final layer, the ‘emergents’, are particularly tall trees that tower above the surrounding canopy e.g. kahitakatea, totara and rimu.

      Abiotic factors such as light intensity, wind strength, and humidity  can all play a role in influencing the growth and success of each plant. Generally, light intensity and wind strength are highest in the emergent and canopy layers, whereas humidity is greatest in the leaf litter and ground cover areas where light is blocked out by the towering trees above.

     Different species are always in competition with one another. As the plants grow, they compete with one another for space, sunlight, water, nutrition and pollinators/seed dispersal partners. To reduce this competition, each species has developed different adaptations that allow them to become specialised to live in a particular niche. Below are common adaptations and the advantage that each adaptation provides. 

Adaptations	Advantage	Suited to which stratum (layer)
Small needle-like leaves	Less surface area for water loss due to transpiration caused by high light intensity, stronger winds and low humidity.	Kahikatea and Rimu – canopy
Shorter thicker leaves	Tougher leaves are able to withstand stronger winds without being damaged.	Kauri – canopy
Woody stems	Strength in woody tissue helps prevent damage from high wind	Lancewood – sub-canopy
Broad flat leaves	Larger surface area allows for the capture of diffuse sunlight which is blocked out by trees higher up.	Coprosma – shrub
Dark green leaves	Additional chloroplasts help to increase the increase the rate of photosynthesis	Coprosma – shrub layer      Harakeke and other ground cover
Thick trunks	Energy spent on strong support systems which protect against high winds; and allows plants to reach higher to get more intense light.	Kauri – Canopy
Growing from another tree’s branches	Gaining support from neighbouring trees help plants reach the canopy while young and removes the need for thick trunks.	Perching lily – Canopy/sub-canopy
Christmas tree juvenile shape and broccoli adult shape	Allows plants to grow up through the shrub layer without being damaged and branch out once older to compete for more intense sunlight	Lancewood – sub-canopy        Kauri and Rimu – Canopy
Bitter, peppery or bad tasting	Prevents herbivory (being   eaten by insects and birds)	Kawakawa, horopito – shrub layer
Fronds that unfurl from koru	Allow plants to open/grow upward and get above plants below in order to obtain more intense sunlight.	Tree ferns and other ferns – Ground layer up to sub-canopy

  The following relationships describe how species interact and serve as biotic factors which affect plant growth.

1) Competition - Plants compete for sunlight and water, both required for photosynthesis. As described above, some behavioural adaptations account for competitive strategies such as the broccoli shaped canopy trees blocking out the sunlight for plants below. Plants also compete for water and the roots of neighbouring trees battle for nutrient rich soil and area where they can absorb rainfall. In one extreme version of competition, the kauri actually loses its leaves which are highly acidic, making the soil around them impossible for seeds of other plants to grow.

2) Commensalism - Some plants benefit from relying on other plant species without causing harm to the neighbouring plant. Epiphytes often arrive at their location through the help of birds. Seeds high in the tree-tops germinate and the plants growing there benefit from greater light intensity. The host tree is not harmed in this type of relationship, nor do they benefit.

3) Exploitation (Parasitisim) -  Lianes and vines may use a host tree for support, reducing the need for them to grow their own supportive tissues when young. Plants such as the climbing rata grow to the top of host trees then block out the sun and strangle their host. Other trees may actually grow roots into their host tree to gain water and nutrition.

4) Mutualism - this is a relationship where both organisms benefit from their close interaction.

Gause’s Law of Competitive Exclusion states that two species that compete for the exact same resources cannot stably coexist. When one species has even the slightest advantage or edge over another then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of one species or an evolutionary shift favouring specific adaptations that allow the competing species to occupy a different ecological niche.

Reasons for stratification:

Although it is common to see New Zealand native plants scattered throughout urban gardens in Auckland, by observing them in a natural forest community, we can examine how each species is uniquely suited to thrive within its realised niche. Considering the abiotic factors, the interspecies relationships and the structural, physiological and behavioural adaptations of species within the forest community, we can uncover reasons for the vertical layering of species that produce the community pattern of stratification.

All plants compete for s_______________, s____________, and w___________. Structural adaptations to variations in __________strength, ________________ intensity and ____________ retention help plants gain the raw materials for photosynthesis. Examples include: type of support tissue (woody/green,) trunk thickness, leaf shape/size, and chlorophyll density. Behavioural adaptations such as epiphytes, vines and lianes using other trees for support to more quickly reach sunlight higher up in the forest allow them to better compete with their neighbours. E_____________ (parasitism), m_____________, and c____________ are some of the relationships that need to be explored, in combination with the adaptations that define an organism’s fundamental niche. When c_____________ is present, organisms best adapted to specific layers dominate, where organisms at the outer reaches of their t________________ zone are pushed out of that vertical layer.

(Sunlight, space, water, light, wind, moisture, exploitation, mutualism, commensalism, competition, tolerance)

Complete the following writing frames to show your understanding of interspecific relationships and how each species is affected.

1.       Perching lilies are often found in the ________________ and _______________________ layers of the forest. In order to live here, they must be adapted to _____________ light intensity and get water from high up in the treetops. Structural adaptations include long, erect v-shaped leaves that are ridged to channel water into the leafy reservoir. Storing water in this way reduces the need for roots to grow in the ground. Because the ___________ is stronger in this layer of the forest, water loss by ________________ occurs quicker, so storing water also helps the plant cope with periods of ________________. Often living in the branches of ______________ and _____________ (name 2 host species) they benefit from getting greater amounts of _______________ which helps them perform photosynthesis more ______________________. Host trees are unharmed. The relationship between the perching lily and its host is called ____________________.

2.       Coprosma are most often found in the _________________ layer of the forest. They come in many varieties, but most have _____________, ________________ leaves with a ________________ surface area than canopy trees. This makes them well adapted to catch the _________________ sunlight that passes through the upper levels of the canopy. These trees have thinner ________________ and less woody tissues than trees in the canopy. This is because they are ________________ from rain and wind experienced higher up by the taller trees. The glossy appearance of coprosma leaves is due to their thick waxy ____________ which helps reduce water loss and also reflects light into the dense _____________ to increase the amount of sunlight absorbed for _______________________.

3.       Cabbage trees, nikau, lancewoods and treeferns all share similar behavioural adaptations to reach the _______________ layer of the forest. Their seeds ________________ under the shade of shrubs which reduce light intensity and help to keep the _____________________ levels of the ground layer high. As they start to grow, juveniles of these species have to compete for space so that they can collect enough sunlight to get energy from photosynthesis. In order to avoid damage to their leaves lancewoods grow long, thin leaves that point ____________________ while ferns unfurl their _______________ by opening many small koru. This allows the dense compact leaves to push up through the shrub layer without being damaged and then to open up allowing for a large _______________________ to absorb sunlight.

4.       In a similar way, emergent trees such as ______________________, _____________ and ________ which rise up through the lower layers and mature to stand above the canopy change their form as they grow. Starting out as a ____________________ shaped plant, these trees avoid damage as they push up through the shrub and sub-canopy layers. Here, they drop their _______________ and begin to grow upward in a _______________ shape. Damage to leaves would reduce the efficiency of photosynthesis and slow their _______________ when young. Influenced by the other plants in their community, they have adapted to rise above the sub-canopy before spreading their branches to increase their chance of getting sunlight. Adults emergent canopy trees in an established forest affect the trees below by reducing the light intensity below them. However, to cope with the intense light and stronger winds, these plants have ___________________ shaped leaves that are short and dense to reduce the loss of water by transpiration.

5.       At the very lowest layer of the forest is the _______________. Plants here benefit from the shade and shelter of plants in higher _________________. However, in order to cope with reduced light _______________ many of these plants have adapted to have higher amounts of _____________________ in their leaves making them dark green This allows for a greater efficiency of light _________________ so that they can perform photosynthesis to gain energy. Other adaptations include having long, broad ___________________ for increased _______________ area for light absorption. Because these plans live closest to insects and larva in the lead litter, some of these plants have the adaptation of producing chemicals that make them ________________ to be eaten. They are able to avoid ______________________ which would reduce their ability to  _____________________________.

Answers:

1.Canopy, sub-canopy, high, wind, transpiration, drought, kauri, kahikatea, sunlight, efficiently, commensalism

2.Shrub, thin, flat, larger, diffuse, trunks, protected, cuticle, foliage, photosynthesis

3.sub-canopy, germinate, humidity, downward, fronds, surface area

4.Kauri, kahikatea, rimu, Christmas tree, branches, broccoli, growth, needle

5. Ground layer, strata, intensity, chlorophyll, absorption, leaves, surface, undesirable, herbivory photosynthesise

Zonation

•Definition: The distribution of species into visible bands or zones along an environmental gradient

•On the rocky shore intertidal species occur in horizontal zones determined by their tolerance to abiotic stresses and interspecific interactions

For the context of this topic we will look at zonation across a rocky shore. The main environmental gradient is time underwater (or time exposed) due to the rising and falling of the tides. this is caused by the lunar cycle and the combination of gravitational forces of the sun and the moon. Generally, species experience two high tides (one every 12.4 hours) and two low tides (one every 12.4 hours) each day.

Abiotic factors:

In addition to temperature, light intensity (exposure time), humidity (hours underwater) which were covered in detail in the study of stratification, the following factors are important to consider:

Salinity - concentration of salt
Terrestrial (land) and marine (underwater) predators
Wave action (physical threat)
Dissolved oxygen availability (for respiration)
Producer availability (food resources for herbivory)

What do these inter-tidal species look like and what are their adaptations? Click on the white boxes in the video to jump to external links which investigate each species in detail. 




Bivalves and Crustaceans (Barnacles) - These organisms are said to be sessile because they they are permanently fixed to the rocky shelf. As a result, they can only eat food which comes to them. They can also only get oxygen from the water they are able to be in contact with. 

     In order to assist in bringing food and oxygen toward them, bivalves  such as oysters and mussels have muscular adaptations called siphons which allow them to pump water containing oxygen and plankton through their bodies. This water passes over internal gills which provide oxygen to their bodies. The gills also have filters which trap food and send it into a gullet (stomach) for digestion.


     
     
     Barnacles on the other hand have long feathery legs that extend out to sweep water and food particles toward their mouth. Barnacles are crustaceans whick look like mini shrimp, which cement their heads to the rocky shelf before growing a shell-like column in which they can live.



     
     Both bivalves and barnacles are able to close themselves inside their hard exteriors. Mussels and oysters close their two shells trapping oxygen rich water inside. This water provides moisture to prevent dessication when they are exposed to sunlight and also provides oxygen for respiration. Barnacles have two plates which they close while the tide is out to protect them from the same dangers. These tough exteriors also help in avoiding predation by oyster borers and whelks which are active during high tide, and predatory birds when the tide is out.


Watch this video which explains how to draw a kite diagram using data to get a representation of relative species distribution within a community where environmental gradients affect the species.

Why do we see species across different zones?

The following reading and questions will help you see how tolerance to changes/extremes in abiotic conditions and interactions/relationships between species affect where different species live. Finding food, wave action, temperature fluctuations, salinity changes, oxygen availability, competition and predation all pose potential threats to intertidal species. However, each species has a set of adaptations which help them cope with these factors in inventive ways and define their unique niche along the rocky shore.

Zonation

To illustrate zonation and the factors that blur the borders between zones, we only need to take a look at the interactions of five animals common to the intertidal zones of our area: two barnacles, a bivalve, a snail and a seastar. Chthamalus (kah-tham-ah-lus) dali is a tiny barnacle found high in the intertidal. Its cousin Balanus glandula, the common acorn barnacle is found a bit lower in the intertidal. Lower still dwells Mytilus, the blue mussel. The whelk snail Nucella lamellosa can often be found mixed in with Balanus and Mytilus, and during low tides we can find Pisaster the seastar at the lower edge of this mix.

The barnacles Chthamalus and Balanus are surrounded by thick outer plates and two inner beak-like plates which clamp tightly shut during the time they are exposed preventing desiccation. Chthamalus is better at controlling its internal temperature and moisture content than Balanus so it can live higher and dryer than Balanus. Both barnacles are filter feeders. The only time they can eat is when they are totally submerged.

At the tide heights where both barnacles are capable of surviving, Balanus is the dominant barnacle. Three to four times as large as Chthamalus, Balanus crushes and crowds out its little cousin. So what we see on the "textbook" shoreline is a higher band of Chthamalus followed by a lower band of Balanus. Chthamalus would prefer to live in a less exposed portion of the intertidal so it could have more time to eat, but it must trade away part of its eating time so it can avoid the lethal actions of Balanus.

Mytilus, the blue mussel, cannot tolerate desiccation as well as the barnacles and prefers a lower intertidal location. At the upper edge of its range where it encounters Balanus, the thick mussel mats grow over and smother the acorn barnacle preventing Balanus from taking advantage of its entire habitat range (though sometimes Balanus prevails by settling on top of mussel shells). The Mytilus story will continue later.

The Nucella snail and Pisaster the seastar LOVE to eat barnacles and mussels. Nucella drills a hole into its prey (which can take many hours) then sucks out the juices. Pisaster uses its numerous powerful tube feet to pry open shells, then inserts its stomach into the shell to eat. Nucella has a thick outer shell and when exposed during low tide, withdraws tightly into its shell, holding on to the rock surface with its powerful foot. Nucella, however, cannot tolerate the same exposure times as the two barnacles so it is limited in how high up it will be able to travel for a barnacle meal. Pisaster is quite vulnerable to desiccation, only able to withstand a fraction of the exposure time that Nucella can. This gives Nucella an advantage at the barnacle banquet because Nucella can stay higher and dryer than Pisaster can. But Nucella feeds only on Balanus not the smaller barnacle Chthamalus. Chthamalus is too high and dry for Nucella thanks to the influence of Balanus which indirectly has spared Chthamalus from predation by Nucella.

Mytilus the mussel (a filter feeder like the barnacles) is capable of living totally submerged in the subtidal but we rarely see it there. Why? Because Pisaster the seastar who also prefers to stay submerged, consumes all the lower mussels first before risking feeding in areas that become exposed during low tide. Remember that Nucella also likes to eat mussels but - here's another twist to the story - Nucella also gets eaten by Pisaster if it moves too low down into the water column. So we have Nucella feeding on Mytilus from above and Pisaster feeding on it from below. Pisaster makes short work of mussel meals whereas Nucella takes hours to eat just one animal. The result is that Mytilus can grow and reproduce faster in the "snail zone" than in the "seastar zone". Consequently we see a neat band of mussels just below the acorn barnacle band. The mussel band upper limit is set by the mussel's exposure tolerance; the lower limit is set by the exposure tolerance of its predator Pisaster.

Homework questions:

1. What is an adaptation of the barnacles Chthamalus and Balanus that helps prevent dessication during exposure?
   
   
   
2. Does Chthamalus occupy its fundamental niche on the rocky shore? Explain.
   
   
   
3. What factor determines the upper limit of Cthamalus’ range?
   
   
   
4. What factor determines the lower limit of Chthamalus’ range?
5. Why are the Pisaster seastars not able to feed on barnacles in the high tidal zone?

Interpreting Kite Diagrams

Describing the pattern of zonation

Looking at the species represented on the kite diagram to the right we can describe the distribution of species in the following way:

The six species in this community show the community pattern of zonation. Zonation is observed when species occupy different areas or zones across an environmental gradient. In this community we can see that species show increasing and decreasing abundance across different depths. For example, species D is found between 820 and 1208 with decreasing abundance. Species E is located in this same shallower zone, but extend to a medium depth of 1750. Species A. B and C are found at all depths, however species A shows a much greater abundance at the mid to deep areas with the greatest population at 1750. Species F is only found in the deepest water.

Relationships and Zonation

Species that occupy different zones (no overlap) may live in similar ways, but are adapted to different abiotic conditions. Example D and F. Competition in their evolutionary past could be the reason for their distribution.

Species that occupy overlapping zones may compete directly with one another. Evidence for this may be seen when one species shows increasing abundance where another shows decreasing abundance. Example F and D.

Species found in the same zones may have feeding relationships (exploitation). Herbivory and predator/prey relationships can be supported by overlapping species distributions on a kite diagram. Examples: A, B and C.

Discuss reasons for the pattern of zonation - Identify adaptations and how they relate to abiotic and biotic factors

In order to fully support reasons for where and species are distributed across the community, adaptations must be identified. Identify special adaptations to deal with the unique challenges associated with different depths. Explain how the abiotic factors that change across the community (example: pressure, oxygen availability, light, temperature, salinity, etc.) and show how the different species cope with this. Identify and discuss adaptations for photosynthesis and/or feeding.